1.
Electronics
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Electronics is the science of controlling electrical energy electrically, in which the electrons have a fundamental role. Commonly, electronic devices contain circuitry consisting primarily or exclusively of active semiconductors supplemented with passive elements, the science of electronics is also considered to be a branch of physics and electrical engineering. The ability of electronic devices to act as switches makes digital information processing possible, until 1950 this field was called radio technology because its principal application was the design and theory of radio transmitters, receivers, and vacuum tubes. Today, most electronic devices use semiconductor components to perform electron control and this article focuses on engineering aspects of electronics. Components are generally intended to be connected together, usually by being soldered to a circuit board. Components may be packaged singly, or in more complex groups as integrated circuits, some common electronic components are capacitors, inductors, resistors, diodes, transistors, etc. Components are often categorized as active or passive, vacuum tubes were among the earliest electronic components. They were almost solely responsible for the revolution of the first half of the Twentieth Century. They took electronics from parlor tricks and gave us radio, television, phonographs, radar, long distance telephony and they played a leading role in the field of microwave and high power transmission as well as television receivers until the middle of the 1980s. Since that time, solid state devices have all but completely taken over, vacuum tubes are still used in some specialist applications such as high power RF amplifiers, cathode ray tubes, specialist audio equipment, guitar amplifiers and some microwave devices. The 608 contained more than 3,000 germanium transistors, thomas J. Watson Jr. ordered all future IBM products to use transistors in their design. From that time on transistors were almost exclusively used for computer logic, circuits and components can be divided into two groups, analog and digital. A particular device may consist of circuitry that has one or the other or a mix of the two types, most analog electronic appliances, such as radio receivers, are constructed from combinations of a few types of basic circuits. Analog circuits use a range of voltage or current as opposed to discrete levels as in digital circuits. The number of different analog circuits so far devised is huge, especially because a circuit can be defined as anything from a single component, analog circuits are sometimes called linear circuits although many non-linear effects are used in analog circuits such as mixers, modulators, etc. Good examples of analog circuits include vacuum tube and transistor amplifiers, one rarely finds modern circuits that are entirely analog. These days analog circuitry may use digital or even microprocessor techniques to improve performance and this type of circuit is usually called mixed signal rather than analog or digital. Sometimes it may be difficult to differentiate between analog and digital circuits as they have elements of both linear and non-linear operation, an example is the comparator which takes in a continuous range of voltage but only outputs one of two levels as in a digital circuit
2.
Measuring instrument
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A measuring instrument is a device for measuring a physical quantity. In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item under study, measuring instruments, and formal test methods which define the instruments use, are the means by which these relations of numbers are obtained. All measuring instruments are subject to varying degrees of instrument error, scientists, engineers and other humans use a vast range of instruments to perform their measurements. These instruments may range from simple objects such as rulers and stopwatches to electron microscopes, virtual instrumentation is widely used in the development of modern measuring instruments. In the past, a common time measuring instrument was the sundial, today, the usual measuring instruments for time are clocks and watches. For highly accurate measurement of time a clock is used. Stop watches are used to measure time in some sports. Energy is measured by an energy meter, examples of energy meters include, An electricity meter measures energy directly in kilowatt hours. A gas meter measures energy indirectly by recording the volume of gas used and this figure can then be converted to a measure of energy by multiplying it by the calorific value of the gas. A physical system that exchanges energy may be described by the amount of energy exchanged per time-interval, for the ranges of power-values see, Orders of magnitude. Action describes energy summed up over the time a process lasts and its dimension is the same as that of an angular momentum. A phototube provides a measurement which permits the calculation of the quantized action of light. This includes basic quantities found in classical- and continuum mechanics, dumpy level Laser line level Spirit level Gyroscope Ballistic pendulum, indirectly by calculation and or gauging Considerations related to electric charge dominate electricity and electronics. Electrical charges interact via a field and that field is called electric if the charge doesnt move. If the charge moves, thus realizing an electric current, especially in a neutral conductor. Electricity can be given a quality — a potential, and electricity has a substance-like property, the electric charge. Energy in elementary electrodynamics is calculated by multiplying the potential by the amount of charge found at that potential, potential times charge, electrometer is often used to reconfirm the phenomenon of contact electricity leading to triboelectric sequences
3.
Voltage
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Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential energy between two points per unit electric charge. The voltage between two points is equal to the work done per unit of charge against an electric field to move the test charge between two points. This is measured in units of volts, voltage can be caused by static electric fields, by electric current through a magnetic field, by time-varying magnetic fields, or some combination of these three. A voltmeter can be used to measure the voltage between two points in a system, often a reference potential such as the ground of the system is used as one of the points. A voltage may represent either a source of energy or lost, used, given two points in space, x A and x B, voltage is the difference in electric potential between those two points. Electric potential must be distinguished from electric energy by noting that the potential is a per-unit-charge quantity. Like mechanical potential energy, the zero of electric potential can be chosen at any point, so the difference in potential, i. e. the voltage, is the quantity which is physically meaningful. The voltage between point A to point B is equal to the work which would have to be done, per unit charge, against or by the electric field to move the charge from A to B. The voltage between the two ends of a path is the energy required to move a small electric charge along that path. Mathematically this is expressed as the integral of the electric field. In the general case, both an electric field and a dynamic electromagnetic field must be included in determining the voltage between two points. Historically this quantity has also called tension and pressure. Pressure is now obsolete but tension is used, for example within the phrase high tension which is commonly used in thermionic valve based electronics. Voltage is defined so that negatively charged objects are pulled towards higher voltages, therefore, the conventional current in a wire or resistor always flows from higher voltage to lower voltage. Current can flow from lower voltage to higher voltage, but only when a source of energy is present to push it against the electric field. This is the case within any electric power source, for example, inside a battery, chemical reactions provide the energy needed for ion current to flow from the negative to the positive terminal. The electric field is not the only factor determining charge flow in a material, the electric potential of a material is not even a well defined quantity, since it varies on the subatomic scale. A more convenient definition of voltage can be found instead in the concept of Fermi level, in this case the voltage between two bodies is the thermodynamic work required to move a unit of charge between them
4.
Electric current
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An electric current is a flow of electric charge. In electric circuits this charge is carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in an ionised gas. The SI unit for measuring a current is the ampere. Electric current is measured using a device called an ammeter, electric currents cause Joule heating, which creates light in incandescent light bulbs. They also create magnetic fields, which are used in motors, inductors and generators, the particles that carry the charge in an electric current are called charge carriers. In metals, one or more electrons from each atom are loosely bound to the atom and these conduction electrons are the charge carriers in metal conductors. The conventional symbol for current is I, which originates from the French phrase intensité de courant, current intensity is often referred to simply as current. The I symbol was used by André-Marie Ampère, after whom the unit of current is named, in formulating the eponymous Ampères force law. The notation travelled from France to Great Britain, where it became standard, in a conductive material, the moving charged particles which constitute the electric current are called charge carriers. In other materials, notably the semiconductors, the carriers can be positive or negative. Positive and negative charge carriers may even be present at the same time, a flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of positive or negative charges. The direction of current is arbitrarily defined as the same direction as positive charges flow. This is called the direction of current I. If the current flows in the direction, the variable I has a negative value. When analyzing electrical circuits, the direction of current through a specific circuit element is usually unknown. Consequently, the directions of currents are often assigned arbitrarily
5.
Microammeter
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An ammeter is a measuring instrument used to measure the current in a circuit. Electric currents are measured in amperes, hence the name, instruments used to measure smaller currents, in the milliampere or microampere range, are designated as milliammeters or microammeters. Early ammeters were laboratory instruments which relied on the Earths magnetic field for operation, by the late 19th century, improved instruments were designed which could be mounted in any position and allowed accurate measurements in electric power systems. The tangent galvanometer was used to measure using this effect. This made these instruments usable only when aligned with the Earths field, sensitivity of the instrument was increased by using additional turns of wire to multiply the effect – the instruments were called multipliers. The DArsonval galvanometer is a moving coil ammeter and it uses magnetic deflection, where current passing through a coil placed in the magnetic field of a permanent magnet causes the coil to move. The modern form of instrument was developed by Edward Weston. The uniform air gap between the core and the permanent magnet poles make the deflection of the meter linearly proportional to current. Basic meter movements can have full-scale deflection for currents from about 25 microamperes to 10 milliamperes, because the magnetic field is polarised, the meter needle acts in opposite directions for each direction of current. A DC ammeter is thus sensitive to which way round it is connected, most are marked with a positive terminal, a moving coil meter indicates the average of a varying current through it, which is zero for AC. For this reason moving-coil meters are only usable directly for DC and this type of meter movement is extremely common for both ammeters and other meters derived from them, such as voltmeters and ohmmeters. Moving magnet ammeters operate on essentially the same principle as moving coil, except that the coil is mounted in the case. Indeed, some Ammeters of this type do not have hairsprings at all, an electrodynamic movement uses an electromagnet instead of the permanent magnet of the dArsonval movement. This instrument can respond to both alternating and direct current and also indicates true RMS for AC, see Wattmeter for an alternative use for this instrument. Moving iron ammeters use a piece of iron which moves when acted upon by the force of a fixed coil of wire. The moving-iron meter was invented by Austrian engineer Friedrich Drexler in 1884 and this type of meter responds to both direct and alternating currents. The iron element consists of a vane attached to a pointer. The deflection of a moving iron meter is proportional to the square of the current, consequently, such meters would normally have a non linear scale, but the iron parts are usually modified in shape to make the scale fairly linear over most of its range
6.
Major appliance
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A major appliance, or domestic appliance, is a large machine in home appliance used for routine housekeeping tasks such as cooking, washing laundry, or food preservation. An appliance is different from a plumbing fixture because it uses electricity or fuel, major appliances differ from small appliances because they are bigger and not portable. They are often considered fixtures and part of estate and as such they are often supplied to tenants as part of otherwise unfurnished rental properties. Major appliances may have electrical connections, connections to gas supplies, or special plumbing. This limits where they can be placed in a home, many major appliances are made of enamel-coated sheet steel which, in the middle 20th century, was usually white. The term white goods in contrast to brown goods, is used, primarily where British English is spoken. In the United States, the white goods can also refer to linens. In New Zealand whiteware may be used, elsewhere a term from pottery, since major appliances in a home consume a significant amount of energy, they have become the objectives of programs to improve their energy efficiency in many countries. Energy efficiency improvements may require changes in construction of the appliances, in the early days of electrification, many major consumer appliances were made by the same companies that made the generation and distribution equipment
7.
Power supply
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A power supply is an electronic device that supplies electric energy to an electrical load. The primary function of a supply is to convert one form of electrical energy to and, as a result. Some power supplies are discrete, stand-alone devices, whereas others are built into larger devices along with their loads, examples of the latter include power supplies found in desktop computers and consumer electronics devices. Every power supply must obtain the energy it supplies to its load, as well as any energy it consumes while performing that task, all power supplies have a power input, which receives energy from the energy source, and a power output that delivers energy to the load. Some power supplies have other types of inputs and outputs as well, for such as external monitoring. Power supplies are categorized in ways, including by functional features. For example, a power supply is one that maintains constant output voltage or current despite variations in load current or input voltage. Conversely, the output of a power supply can change significantly when its input voltage or load current changes. Adjustable power supplies allow the voltage or current to be programmed by mechanical controls, or by means of a control input. An adjustable regulated power supply is one that is adjustable and regulated. Power supplies are packaged in different ways and classified accordingly, a bench power supply is a stand-alone desktop unit used in applications such as circuit test and development. Open frame power supplies have only a partial mechanical enclosure, sometimes consisting of only a mounting base, rack mount power supplies are designed to be secured into standard electronic equipment racks. An integrated power supply is one that shares a common printed circuit board with its load, power supplies can be broadly divided into linear and switching types. Linear power converters process the power directly, with all active power conversion components operating in their linear operating regions. In switching power converters, the power is converted to AC or to DC pulses before processing. A DC power supply is one that supplies a constant DC voltage to its load, depending on its design, a DC power supply may be powered from a DC source or from an AC source such as the power mains. Some DC power supplies use AC mains electricity as an energy source, such power supplies will sometimes employ a transformer to convert the input voltage to a higher or lower AC voltage. A rectifier is used to convert the output voltage to a varying DC voltage
8.
United States dollar
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The United States dollar is the official currency of the United States and its insular territories per the United States Constitution. It is divided into 100 smaller cent units, the circulating paper money consists of Federal Reserve Notes that are denominated in United States dollars. The U. S. dollar was originally commodity money of silver as enacted by the Coinage Act of 1792 which determined the dollar to be 371 4/16 grain pure or 416 grain standard silver, the currency most used in international transactions, it is the worlds primary reserve currency. Several countries use it as their currency, and in many others it is the de facto currency. Besides the United States, it is used as the sole currency in two British Overseas Territories in the Caribbean, the British Virgin Islands and Turks and Caicos Islands. A few countries use the Federal Reserve Notes for paper money, while the country mints its own coins, or also accepts U. S. coins that can be used as payment in U. S. dollars. After Nixon shock of 1971, USD became fiat currency, Article I, Section 8 of the U. S. Constitution provides that the Congress has the power To coin money, laws implementing this power are currently codified at 31 U. S. C. Section 5112 prescribes the forms in which the United States dollars should be issued and these coins are both designated in Section 5112 as legal tender in payment of debts. The Sacagawea dollar is one example of the copper alloy dollar, the pure silver dollar is known as the American Silver Eagle. Section 5112 also provides for the minting and issuance of other coins and these other coins are more fully described in Coins of the United States dollar. The Constitution provides that a regular Statement and Account of the Receipts and that provision of the Constitution is made specific by Section 331 of Title 31 of the United States Code. The sums of money reported in the Statements are currently being expressed in U. S. dollars, the U. S. dollar may therefore be described as the unit of account of the United States. The word dollar is one of the words in the first paragraph of Section 9 of Article I of the Constitution, there, dollars is a reference to the Spanish milled dollar, a coin that had a monetary value of 8 Spanish units of currency, or reales. In 1792 the U. S. Congress passed a Coinage Act, Section 20 of the act provided, That the money of account of the United States shall be expressed in dollars, or units. And that all accounts in the offices and all proceedings in the courts of the United States shall be kept and had in conformity to this regulation. In other words, this act designated the United States dollar as the unit of currency of the United States, unlike the Spanish milled dollar the U. S. dollar is based upon a decimal system of values. Both one-dollar coins and notes are produced today, although the form is significantly more common
9.
Calibration
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Calibration in measurement technology and metrology is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known accuracy, strictly, the term calibration means just the act of comparison, and does not include any subsequent adjustment. The calibration standard is normally traceable to a national standard held by a National Metrological Institute and this definition states that the calibration process is purely a comparison, but introduces the concept of Measurement uncertainty in relating the accuracies of the device under test and the standard. The increasing need for accuracy and uncertainty and the need to have consistent. In many countries a National Metrology Institute will exist which will maintain primary standards of measurement which will be used to provide traceability to customers instruments by calibration. The NMI supports the metrological infrastructure in that country by establishing an unbroken chain, examples of National Metrology Institutes are NPL in the UK, NIST in the United States, PTB in Germany and many others. This may be done by national standards laboratories operated by the government or by private firms offering metrology services, quality management systems call for an effective metrology system which includes formal, periodic, and documented calibration of all measuring instruments. ISO9000 and ISO17025 standards require that these actions are to a high level. To communicate the quality of a calibration the calibration value is often accompanied by a traceable uncertainty statement to a confidence level. This is evaluated through careful uncertainty analysis, some times a DFS is required to operate machinery in a degraded state. Whenever this does happen, it must be in writing and authorized by a manager with the assistance of a calibration technician. Measuring devices and instruments are categorized according to the quantities they are designed to measure. These vary internationally, e. g. NIST 150-2G in the U. S. the standard instrument for each test device varies accordingly, e. g. a dead weight tester for pressure gauge calibration and a dry block temperature tester for temperature gauge calibration. g. This is the perception of the instruments end-user, however, very few instruments can be adjusted to exactly match the standards they are compared to. For the vast majority of calibrations, the process is actually the comparison of an unknown to a known. The calibration process begins with the design of the instrument that needs to be calibrated. The design has to be able to hold a calibration through its calibration interval, in other words, the design has to be capable of measurements that are within engineering tolerance when used within the stated environmental conditions over some reasonable period of time. Having a design with these characteristics increases the likelihood of the measuring instruments performing as expected
10.
Avometer
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Avometer is a British trademark for a line of multimeters and electrical measuring instruments, the brand is now owned by the Megger Group Limited. The first Avometer was made by the Automatic Coil Winder and Electrical Equipment Co. in 1923, possibly the best known multimeter of the range was the Model 8, which was produced in various versions from the May 1951 until 2008, the last version was the Mark 7. The multimeter is often called simply an AVO, because the company carries the first letters of amps, volts. Mr. MacAdie was born in the county of Caithness in northern Scotland, the original Avometer was designed to measure direct current, direct voltage and resistance. All ranges could be selected by a rotary switch which set both the function and the range value. A second switch brought a rheostat into circuit in series with the instrument and could be used to control the current through a device under test and it had a knife edge pointer and an anti-parallax mirror. Additional patents were taken out in Czechoslovakia, Austria, France, Germany, a US patent followed in 1926 The case of the original Avometer was a comb-jointed oak box with an ebonite lower front panel. The upper part of the front panel was cast aluminium, after around three years production, the volume of sales was sufficient to justify a redesign of the instrument, now with a movement whose full-scale current was 6mA. The redesigned meter had 13 ranges and was constructed on a one piece phenolic moulding with the kidney shaped window. The back case was a deep drawn aluminium can on the back of which was a summary of the operating instructions, the movement was originally protected by a short length of wire, selected to act as a fuse, soldered to supports on the back of the movement. Later versions had a calibrated, screw-in, fuse on the front panel, unlike many similar multimeter designs, all Universal Avometers, with the exception of the short-lived High Resistance Avometer, could measure up to either 10A or 12A depending on the model. From 1933, the number of voltage and current ranges in Universal Avometers was doubled by incorporating a dual sensitivity movement circuit. The higher sensitivity was selected by a button switch marked ÷2 signifying that the pointer indication should be halved. For the Model 8, this feature was not used but the button was retained for reversing the direction of deflection of the moving coil. A design feature of Avometers was simplicity of use and towards this end, however, the Avometer HR had additional 2500V and ranges which used the corresponding 1000V ranges, and were connected through two additional terminals at the top corners of the front panel. This feature was continued in the Model 8 and, with an increase to 3000V to match their 1 -3 -10 ranges sequence, in the Model 9, Marks II and IV and the Model 8 Mark V. The 3000V ranges were deleted in the Model 8 Marks 6 and 7 due to concerns for compliance with safety standards. This also led to a significant cost saving by eliminating the high voltage multiplier resistors, as an ohmmeter the Model 8 Mark II measures from 1 Ω up to 20 MΩ in three ranges
11.
Galvanometer
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A galvanometer is an electromechanical instrument for detecting and measuring electric current. The most common use of galvanometers was as analog measuring instruments, called ammeters, a galvanometer works as an actuator, by producing a rotary deflection, in response to electric current flowing through a coil in a constant magnetic field. Galvanometers developed from the observation that the needle of a compass is deflected near a wire that has electric current flowing through it. They were the first instruments used to detect and measure small amounts of electric currents, the name comes from the Italian electricity researcher Luigi Galvani, who in 1791 discovered the principle of the frog galvanoscope – that electric current would make the legs of a dead frog jerk. Sensitive galvanometers have been essential for the development of science and technology in many fields, today the main type of galvanometer mechanism, still in use, is the moving coil, DArsonval/Weston type. Modern galvanometers, of the DArsonval/Weston type, are constructed with a small pivoting coil of wire in the field of a permanent magnet, the coil is attached to a thin pointer that traverses a calibrated scale. A tiny torsion spring pulls the coil and pointer to the zero position, when a direct current flows through the coil, the coil generates a magnetic field. This field acts against the permanent magnet, the coil twists, pushing against the spring, and moves the pointer. The hand points at a scale indicating the electric current, careful design of the pole pieces ensures that the magnetic field is uniform, so that the angular deflection of the pointer is proportional to the current. A useful meter generally contains provision for damping the mechanical resonance of the coil and pointer. The basic sensitivity of a meter might be, for instance,100 microamperes full scale, such meters are often calibrated to read some other quantity that can be converted to a current of that magnitude. The use of current dividers, often called shunts, allows a meter to be calibrated to measure larger currents, a meter can be calibrated as a DC voltmeter if the resistance of the coil is known by calculating the voltage required to generate a full scale current. A meter can be configured to read other voltages by putting it in a voltage divider circuit and this is generally done by placing a resistor in series with the meter coil. A meter can be used to resistance by placing it in series with a known voltage. In a preparatory step, the circuit is completed and the resistor adjusted to produce full scale deflection. When an unknown resistor is placed in series in the circuit the current will be less than full scale and an appropriately calibrated scale can display the value of the previously unknown resistor. Because the pointer of the meter is usually a distance above the scale of the meter. To counter this, some include a mirror along the markings of the principal scale
12.
Wheatstone bridge
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A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. The primary benefit of a bridge is its ability to provide extremely accurate measurements. Its operation is similar to the original potentiometer, the Wheatstone bridge was invented by Samuel Hunter Christie in 1833 and improved and popularized by Sir Charles Wheatstone in 1843. One of the Wheatstone bridges initial uses was for the purpose of soils analysis, in the figure, R x is the unknown resistance to be measured, R1, R2, and R3 are resistors of known resistance and the resistance of R2 is adjustable. If the bridge is unbalanced, the direction of the current indicates whether R2 is too high or too low, R2 is varied until there is no current through the galvanometer, which then reads zero. Detecting zero current with a galvanometer can be done to extremely high accuracy, therefore, if R1, R2, and R3 are known to high precision, then R x can be measured to high precision. Very small changes in R x disrupt the balance and are readily detected and this setup is frequently used in strain gauge and resistance thermometer measurements, as it is usually faster to read a voltage level off a meter than to adjust a resistance to zero the voltage. The equation for this is, V G = V s where VG is the voltage of node D relative to node B, the Wheatstone bridge illustrates the concept of a difference measurement, which can be extremely accurate. Variations on the Wheatstone bridge can be used to measure capacitance, inductance, impedance and other quantities, such as the amount of gases in a sample. The Kelvin bridge was adapted from the Wheatstone bridge for measuring very low resistances. The concept was extended to alternating current measurements by James Clerk Maxwell in 1865, the Wheatstone bridge is the fundamental bridge, but there are other modifications that can be made to measure various kinds of resistances when the fundamental Wheatstone bridge is not suitable. Some of the modifications are, Carey Foster bridge, for measuring small resistances Kelvin bridge, for measuring small four-terminal resistances Maxwell bridge, Wheatstone Bridge – Interactive Tutorial National High Magnetic Field Laboratory Test Set I-49
13.
Radio receiver
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In radio communications, a radio receiver is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna, the antenna intercepts radio waves and converts them to tiny alternating currents which are applied to the receiver, and the receiver extracts the desired information. The information produced by the receiver may be in the form of sound, a radio receiver may be a separate piece of electronic equipment, or an electronic circuit within another device. The most familiar form of radio receiver is a broadcast receiver, often just called a radio, the sound is produced either by a loudspeaker in the radio or an earphone which plugs into a jack on the radio. The radio requires electric power, provided either by batteries inside the radio or a cord which plugs into an electric outlet. All radios have a control to adjust the loudness of the audio. The frequency of radio stations is usually listed prominently in their advertising, in order to select a particular station to receive, the radio is adjusted to the frequency of the desired transmitter. In some radios this is done by the user turning a tuning knob until the station is heard in the radios loudspeaker. In most countries radio broadcasting is permitted using two different methods of modulation, that is, methods of adding the signal to the radio wave, AM and FM. In amplitude modulation the strength of the signal is varied by the audio signal. AM broadcasting is permitted on AM broadcast bands between 148 and 283 kHz in the low range and 526 and 1706 kHz in the medium frequency range of the radio spectrum. In frequency modulation the frequency of the signal is varied slightly by the audio signal. FM broadcasting is permitted in the FM broadcast bands between about 65 and 108 MHz in the high frequency range. The exact frequency ranges vary somewhat in different countries, radios sold in each receive the correct frequency range for that country. Most broadcast radios, called AM/FM radios, can receive both AM and FM bands, and have a switch to select which band to receive. Limited AM broadcasting is permitted in parts of the high frequency band called the shortwave band. Shortwave listening requires a receiver that can receive these bands, called a shortwave receiver, at these frequencies, radio waves transmitted into the sky can reflect from a layer in the atmosphere called the ionosphere, returning to earth at transcontinental distances. So shortwaves are used for long distance international broadcasting, often by governmental public service broadcasting organizations like the BBC, due to their lower frequency, AM radio stations can often be received at longer distances than FM stations, at hundreds of miles
14.
Vacuum tube
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In electronics, a vacuum tube, an electron tube, or just a tube, or valve, is a device that controls electric current between electrodes in an evacuated container. Vacuum tubes mostly rely on thermionic emission of electrons from a hot filament or a cathode heated by the filament and this type is called a thermionic tube or thermionic valve. A phototube, however, achieves electron emission through the photoelectric effect, the simplest vacuum tube, the diode, contains only a heater, a heated electron-emitting cathode, and a plate. Current can only flow in one direction through the device between the two electrodes, as electrons emitted by the travel through the tube and are collected by the anode. Adding one or more control grids within the tube allows the current between the cathode and anode to be controlled by the voltage on the grid or grids, Tubes with grids can be used for many purposes, including amplification, rectification, switching, oscillation, and display. In the 1940s the invention of devices made it possible to produce solid-state devices, which are smaller, more efficient, more reliable, more durable. Hence, from the mid-1950s solid-state devices such as transistors gradually replaced tubes, the cathode-ray tube remained the basis for televisions and video monitors until superseded in the 21st century. However, there are still a few applications for which tubes are preferred to semiconductors, for example, the used in microwave ovens. One classification of vacuum tubes is by the number of active electrodes, a device with two active elements is a diode, usually used for rectification. Devices with three elements are used for amplification and switching. Additional electrodes create tetrodes, pentodes, and so forth, which have additional functions made possible by the additional controllable electrodes. X-ray tubes are vacuum tubes. Phototubes and photomultipliers rely on electron flow through a vacuum, though in those cases electron emission from the cathode depends on energy from photons rather than thermionic emission, since these sorts of vacuum tubes have functions other than electronic amplification and rectification they are described in their own articles. A vacuum tube consists of two or more electrodes in a vacuum inside an airtight enclosure, most tubes have glass envelopes, though ceramic and metal envelopes have been used. The electrodes are attached to leads which pass through the envelope via an airtight seal, Tubes were a frequent cause of failure in electronic equipment, and consumers were expected to be able to replace tubes themselves. In addition to the terminals, some tubes had an electrode terminating at a top cap. The principal reason for doing this was to avoid leakage resistance through the tube base, the bases were commonly made with phenolic insulation which performs poorly as an insulator in humid conditions. There was even a design that had two top cap connections
15.
Invention
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An invention is a unique or novel device, method, composition or process. The invention process is a process within an overall engineering and product development process and it may be an improvement upon a machine or product or a new process for creating an object or a result. An invention that achieves a unique function or result may be a radical breakthrough. Such works are novel and not obvious to others skilled in the same field, an inventor may be taking a big step in success or failure. A patent legally protects the property rights of the inventor. The rules and requirements for patenting an invention vary from country to country, another meaning of invention is cultural invention, which is an innovative set of useful social behaviours adopted by people and passed on to others. The Institute for Social Inventions collected many such ideas in magazines, Invention is also an important component of artistic and design creativity. Inventions often extend the boundaries of knowledge, experience or capability. Brainstorming also can spark new ideas for an invention, collaborative creative processes are frequently used by engineers, designers, architects and scientists. Co-inventors are frequently named on patents, in addition, many inventors keep records of their working process - notebooks, photos, etc. including Leonardo da Vinci, Galileo Galilei, Evangelista Torricelli, Thomas Jefferson and Albert Einstein. In the process of developing an invention, the idea may change. The invention may become simpler, more practical, it may expand, working on one invention can lead to others too. History shows that turning the concept of an invention into a device is not always swift or direct. Inventions may also more useful after time passes and other changes occur. For example, the became more useful once powered flight was a reality. Invention is often a creative process, an open and curious mind allows an inventor to see beyond what is known. Seeing a new possibility, connection, or relationship can spark an invention, inventive thinking frequently involves combining concepts or elements from different realms that would not normally be put together. Sometimes inventors disregard the boundaries between distinctly separate territories or fields, several concepts may be considered when thinking about invention
16.
Telecommunication
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Telecommunication is the transmission of signs, signals, messages, writings, images and sounds or intelligence of any nature by wire, radio, optical or other electromagnetic systems. Telecommunication occurs when the exchange of information between communication participants includes the use of technology and it is transmitted either electrically over physical media, such as cables, or via electromagnetic radiation. Such transmission paths are divided into communication channels which afford the advantages of multiplexing. The term is used in its plural form, telecommunications. Early means of communicating over a distance included visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, other examples of pre-modern long-distance communication included audio messages such as coded drumbeats, lung-blown horns, and loud whistles. Zworykin, John Logie Baird and Philo Farnsworth, the word telecommunication is a compound of the Greek prefix tele, meaning distant, far off, or afar, and the Latin communicare, meaning to share. Its modern use is adapted from the French, because its use was recorded in 1904 by the French engineer. Communication was first used as an English word in the late 14th century, in the Middle Ages, chains of beacons were commonly used on hilltops as a means of relaying a signal. Beacon chains suffered the drawback that they could pass a single bit of information. One notable instance of their use was during the Spanish Armada, in 1792, Claude Chappe, a French engineer, built the first fixed visual telegraphy system between Lille and Paris. However semaphore suffered from the need for skilled operators and expensive towers at intervals of ten to thirty kilometres, as a result of competition from the electrical telegraph, the last commercial line was abandoned in 1880. Homing pigeons have occasionally used throughout history by different cultures. Pigeon post is thought to have Persians roots and was used by the Romans to aid their military, frontinus said that Julius Caesar used pigeons as messengers in his conquest of Gaul. The Greeks also conveyed the names of the victors at the Olympic Games to various cities using homing pigeons, in the early 19th century, the Dutch government used the system in Java and Sumatra. And in 1849, Paul Julius Reuter started a service to fly stock prices between Aachen and Brussels, a service that operated for a year until the gap in the telegraph link was closed. Sir Charles Wheatstone and Sir William Fothergill Cooke invented the telegraph in 1837. Also, the first commercial electrical telegraph is purported to have constructed by Wheatstone and Cooke. Both inventors viewed their device as an improvement to the electromagnetic telegraph not as a new device, samuel Morse independently developed a version of the electrical telegraph that he unsuccessfully demonstrated on 2 September 1837
17.
Ampere
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The ampere, often shortened to amp, is a unit of electric current. In the International System of Units the ampere is one of the seven SI base units and it is named after André-Marie Ampère, French mathematician and physicist, considered the father of electrodynamics. SI defines the ampere in terms of base units by measuring the electromagnetic force between electrical conductors carrying electric current. The ampere was then defined as one coulomb of charge per second, in SI, the unit of charge, the coulomb, is defined as the charge carried by one ampere during one second. In the future, the SI definition may shift back to charge as the base unit, ampères force law states that there is an attractive or repulsive force between two parallel wires carrying an electric current. This force is used in the definition of the ampere. The SI unit of charge, the coulomb, is the quantity of electricity carried in 1 second by a current of 1 ampere, conversely, a current of one ampere is one coulomb of charge going past a given point per second,1 A =1 C s. In general, charge Q is determined by steady current I flowing for a time t as Q = It, constant, instantaneous and average current are expressed in amperes and the charge accumulated, or passed through a circuit over a period of time is expressed in coulombs. The relation of the ampere to the coulomb is the same as that of the watt to the joule, the ampere was originally defined as one tenth of the unit of electric current in the centimetre–gram–second system of units. That unit, now known as the abampere, was defined as the amount of current that generates a force of two dynes per centimetre of length between two wires one centimetre apart. The size of the unit was chosen so that the derived from it in the MKSA system would be conveniently sized. The international ampere was a realization of the ampere, defined as the current that would deposit 0.001118 grams of silver per second from a silver nitrate solution. Later, more accurate measurements revealed that this current is 0.99985 A, at present, techniques to establish the realization of an ampere have a relative uncertainty of approximately a few parts in 107, and involve realizations of the watt, the ohm and the volt. Rather than a definition in terms of the force between two current-carrying wires, it has proposed that the ampere should be defined in terms of the rate of flow of elementary charges. Since a coulomb is equal to 6. 2415093×1018 elementary charges. The proposed change would define 1 A as being the current in the direction of flow of a number of elementary charges per second. In 2005, the International Committee for Weights and Measures agreed to study the proposed change, the new definition was discussed at the 25th General Conference on Weights and Measures in 2014 but for the time being was not adopted. The current drawn by typical constant-voltage energy distribution systems is usually dictated by the power consumed by the system, for this reason the examples given below are grouped by voltage level
18.
Ohm
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The ohm is the SI derived unit of electrical resistance, named after German physicist Georg Simon Ohm. The definition of the ohm was revised several times, today the definition of the ohm is expressed from the quantum Hall effect. In many cases the resistance of a conductor in ohms is approximately constant within a range of voltages, temperatures. In alternating current circuits, electrical impedance is also measured in ohms, the siemens is the SI derived unit of electric conductance and admittance, also known as the mho, it is the reciprocal of resistance in ohms. The power dissipated by a resistor may be calculated from its resistance, non-linear resistors have a value that may vary depending on the applied voltage. The rapid rise of electrotechnology in the last half of the 19th century created a demand for a rational, coherent, consistent, telegraphers and other early users of electricity in the 19th century needed a practical standard unit of measurement for resistance. Two different methods of establishing a system of units can be chosen. Various artifacts, such as a length of wire or a standard cell, could be specified as producing defined quantities for resistance, voltage. This latter method ensures coherence with the units of energy, defining a unit for resistance that is coherent with units of energy and time in effect also requires defining units for potential and current. Some early definitions of a unit of resistance, for example, the absolute-units system related magnetic and electrostatic quantities to metric base units of mass, time, and length. These units had the advantage of simplifying the equations used in the solution of electromagnetic problems. However, the CGS units turned out to have impractical sizes for practical measurements, various artifact standards were proposed as the definition of the unit of resistance. In 1860 Werner Siemens published a suggestion for a reproducible resistance standard in Poggendorffs Annalen der Physik und Chemie and he proposed a column of pure mercury, of one square millimetre cross section, one metre long, Siemens mercury unit. However, this unit was not coherent with other units, one proposal was to devise a unit based on a mercury column that would be coherent – in effect, adjusting the length to make the resistance one ohm. Not all users of units had the resources to carry out experiments to the required precision. The BAAS in 1861 appointed a committee including Maxwell and Thomson to report upon Standards of Electrical Resistance, in the third report of the committee,1864, the resistance unit is referred to as B. A. unit, or Ohmad. By 1867 the unit is referred to as simply Ohm, the B. A. ohm was intended to be 109 CGS units but owing to an error in calculations the definition was 1. 3% too small. The error was significant for preparation of working standards, on September 21,1881 the Congrès internationale délectriciens defined a practical unit of Ohm for the resistance, based on CGS units, using a mercury column at zero deg
19.
Nonlinear system
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In mathematics and physical sciences, a nonlinear system is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, physicists and mathematicians, nonlinear systems may appear chaotic, unpredictable or counterintuitive, contrasting with the much simpler linear systems. In other words, in a system of equations, the equation to be solved cannot be written as a linear combination of the unknown variables or functions that appear in them. Systems can be defined as non-linear, regardless of whether or not known linear functions appear in the equations. In particular, an equation is linear if it is linear in terms of the unknown function and its derivatives. As nonlinear equations are difficult to solve, nonlinear systems are approximated by linear equations. This works well up to some accuracy and some range for the input values and it follows that some aspects of the behavior of a nonlinear system appear commonly to be counterintuitive, unpredictable or even chaotic. Although such chaotic behavior may resemble random behavior, it is not random. For example, some aspects of the weather are seen to be chaotic and this nonlinearity is one of the reasons why accurate long-term forecasts are impossible with current technology. Some authors use the term nonlinear science for the study of nonlinear systems and this is disputed by others, Using a term like nonlinear science is like referring to the bulk of zoology as the study of non-elephant animals. In mathematics, a function f is one which satisfies both of the following properties, Additivity or superposition, f = f + f, Homogeneity. Additivity implies homogeneity for any rational α, and, for continuous functions, for a complex α, homogeneity does not follow from additivity. For example, a map is additive but not homogeneous. The equation is called homogeneous if C =0, if f contains differentiation with respect to x, the result will be a differential equation. Nonlinear algebraic equations, which are also called polynomial equations, are defined by equating polynomials to zero, for example, x 2 + x −1 =0. For a single equation, root-finding algorithms can be used to find solutions to the equation. However, systems of equations are more complicated, their study is one motivation for the field of algebraic geometry. It is even difficult to decide whether a given system has complex solutions
20.
Voltmeter
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A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit, a voltmeter in a circuit diagram is represented by the letter V in a circle. Voltmeters are made in a range of styles. Instruments permanently mounted in a panel are used to monitor generators or other fixed apparatus, portable instruments, usually equipped to also measure current and resistance in the form of a multimeter, are standard test instruments used in electrical and electronics work. Any measurement that can be converted to a voltage can be displayed on a meter that is calibrated, for example, pressure, temperature. General purpose analog voltmeters may have an accuracy of a few percent of full scale, digital meters can be made with high accuracy, typically better than 1%. Specially calibrated test instruments have higher accuracies, with instruments capable of measuring to accuracies of a few parts per million. Meters using amplifiers can measure tiny voltages of microvolts or less, part of the problem of making an accurate voltmeter is that of calibration to check its accuracy. In laboratories, the Weston Cell is used as a voltage for precision work. Precision voltage references are based on electronic circuits. A moving coil galvanometer can be used as a voltmeter by inserting a resistor in series with the instrument, the galvanometer has a coil of fine wire suspended in a strong magnetic field. When an electric current is applied, the interaction of the field of the coil and of the stationary magnet creates a torque. The torque is proportional to the current through the coil, the coil rotates, compressing a spring that opposes the rotation. The deflection of the coil is proportional to the current, which in turn is proportional to the applied voltage. One of the objectives of the instrument is to disturb the circuit as little as possible. This is achieved by using a galvanometer in series with a high resistance. The sensitivity of such a meter can be expressed as ohms per volt, for multi-range instruments, the input resistance varies as the instrument is switched to different ranges. Moving-coil instruments with a permanent-magnet field respond only to direct current, measurement of AC voltage requires a rectifier in the circuit so that the coil deflects in only one direction
21.
Electrical impedance
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Electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied. In quantitative terms, it is the ratio of the voltage to the current in an alternating current circuit. Impedance extends the concept of resistance to AC circuits, and possesses both magnitude and phase, unlike resistance, which has only magnitude. When a circuit is driven with direct current, there is no distinction between impedance and resistance, the latter can be thought of as impedance with zero phase angle. The impedance caused by two effects is collectively referred to as reactance and forms the imaginary part of complex impedance whereas resistance forms the real part. The symbol for impedance is usually Z and it may be represented by writing its magnitude, however, cartesian complex number representation is often more powerful for circuit analysis purposes. The term impedance was coined by Oliver Heaviside in July 1886, arthur Kennelly was the first to represent impedance with complex numbers in 1893. Impedance is defined as the frequency ratio of the voltage to the current. In other words, it is the voltage–current ratio for a complex exponential at a particular frequency ω. In general, impedance will be a number, with the same units as resistance. For a sinusoidal current or voltage input, the form of the complex impedance relates the amplitude and phase of the voltage. In particular, The magnitude of the impedance is the ratio of the voltage amplitude to the current amplitude. The phase of the impedance is the phase shift by which the current lags the voltage. The reciprocal of impedance is admittance, Impedance is represented as a complex quantity Z and the term complex impedance may be used interchangeably. J is the unit, and is used instead of i in this context to avoid confusion with the symbol for electric current. In Cartesian form, impedance is defined as Z = R + j X where the part of impedance is the resistance R. Where it is needed to add or subtract impedances, the form is more convenient, but when quantities are multiplied or divided. A circuit calculation, such as finding the total impedance of two impedances in parallel, may require conversion between forms several times during the calculation, conversion between the forms follows the normal conversion rules of complex numbers
22.
Amplifier
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An amplifier, electronic amplifier or amp is an electronic device that can increase the power of a signal. An amplifier functions by taking power from a supply and controlling the output to match the input signal shape. In this sense, an amplifier modulates the output of the power supply based upon the properties of the input signal, an amplifier is effectively the opposite of an attenuator, while an amplifier provides gain, an attenuator provides loss. An amplifier can either be a piece of equipment or an electrical circuit contained within another device. Amplification is fundamental to modern electronics, and amplifiers are used in almost all electronic equipment. Amplifiers can be categorized in different ways, another is which quantity, voltage or current is being amplified, amplifiers can be divided into voltage amplifiers, current amplifiers, transconductance amplifiers, and transresistance amplifiers. A further distinction is whether the output is a linear or nonlinear representation of the input, amplifiers can also be categorized by their physical placement in the signal chain. The first practical device that could amplify was the triode vacuum tube, invented in 1906 by Lee De Forest. Vacuum tubes were used in almost all amplifiers until the 1960s–1970s when the transistor, invented in 1947, today most amplifiers use transistors, but vacuum tubes continue to be used in some applications. Before the invention of electronic amplifiers, mechanically coupled carbon microphones were used as amplifiers in telephone repeaters. After the turn of the century it was found that negative resistance mercury lamps could amplify, the first practical electronic device that could amplify was the Audion vacuum tube, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912. The terms amplifier and amplification were first used for this new capability around 1915 when triodes became widespread, the amplifying vacuum tube revolutionized electrical technology, creating the new field of electronics, the technology of active electrical devices. It made possible long distance lines, public address systems, radio broadcasting, talking motion pictures, practical audio recording, radar, television. For 50 years virtually all electronic devices used vacuum tubes. Early tube amplifiers often had positive feedback, which could increase gain but also make the amplifier unstable, much of the mathematical theory of amplifiers was developed at Bell Telephone Laboratories during the 1920s to 1940s. Other advances in the theory of amplification were made by Harry Nyquist, the vacuum tube was the only amplifying device for 40 years, and dominated electronics until 1947, when the first transistor, the BJT, was invented. Today most amplifiers use transistors, but vacuum tubes are used in some high power applications such as radio transmitters. All amplifiers have gain, a factor that relates the magnitude of some property of the output signal to a property of the input signal
23.
Transistor
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A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit, a voltage or current applied to one pair of the transistors terminals controls the current through another pair of terminals. Because the controlled power can be higher than the controlling power, today, some transistors are packaged individually, but many more are found embedded in integrated circuits. The transistor is the building block of modern electronic devices. Julius Edgar Lilienfeld patented a field-effect transistor in 1926 but it was not possible to construct a working device at that time. The first practically implemented device was a point-contact transistor invented in 1947 by American physicists John Bardeen, Walter Brattain, the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things. The transistor is on the list of IEEE milestones in electronics, and Bardeen, Brattain, the thermionic triode, a vacuum tube invented in 1907, enabled amplified radio technology and long-distance telephony. The triode, however, was a device that consumed a substantial amount of power. Physicist Julius Edgar Lilienfeld filed a patent for a transistor in Canada in 1925. Lilienfeld also filed patents in the United States in 1926 and 1928. However, Lilienfeld did not publish any research articles about his devices nor did his patents cite any examples of a working prototype. In 1934, German inventor Oskar Heil patented a device in Europe. Solid State Physics Group leader William Shockley saw the potential in this, the term transistor was coined by John R. Pierce as a contraction of the term transresistance. Instead, what Bardeen, Brattain, and Shockley invented in 1947 was the first point-contact transistor, Mataré had previous experience in developing crystal rectifiers from silicon and germanium in the German radar effort during World War II. Using this knowledge, he began researching the phenomenon of interference in 1947, realizing that Bell Labs scientists had already invented the transistor before them, the company rushed to get its transistron into production for amplified use in Frances telephone network. The first bipolar junction transistors were invented by Bell labs William Shockley, on April 12,1950, Bell Labs chemists Gordon Teal and Morgan Sparks had successfully produced a working bipolar NPN junction amplifying germanium transistor. Bell Labs had made this new sandwich transistor discovery announcement, in a release on July 4,1951. The first high-frequency transistor was the surface-barrier germanium transistor developed by Philco in 1953 and these were made by etching depressions into an N-type germanium base from both sides with jets of Indium sulfate until it was a few ten-thousandths of an inch thick
24.
Field-effect transistor
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The field-effect transistor is a transistor that uses an electric field to control the electrical behaviour of the device. FETs are also known as unipolar transistors since they involve single-carrier-type operation, many different implementations of field effect transistors exist. Field effect transistors generally display very high impedance at low frequencies. The conductivity between the drain and source terminals is controlled by a field in the device, which is generated by the voltage difference between the body and the gate of the device. The MOSFET, which superseded the JFET and had a profound effect on digital electronic development, was invented by Dawon Kahng. The device consists of a channel through which charge carriers, electrons or holes. Source and drain terminal conductors are connected to the semiconductor through ohmic contacts, the conductivity of the channel is a function of the potential applied across the gate and source terminals. The FETs three terminals are, Source, through which the carriers enter the channel, conventionally, current entering the channel at S is designated by IS. Drain, through which the carriers leave the channel, conventionally, current entering the channel at D is designated by ID. Gate, the terminal that modulates the channel conductivity, by applying voltage to G, one can control ID. All FETs have source, drain, and gate terminals that correspond roughly to the emitter, collector, most FETs have a fourth terminal called the body, base, bulk, or substrate. The size of the gate, length L in the diagram, is the distance between source and drain, the width is the extension of the transistor, in the direction perpendicular to the cross section in the diagram. Typically the width is larger than the length of the gate. A gate length of 1 µm limits the frequency to about 5 GHz,0.2 µm to about 30 GHz. The names of the terminals refer to their functions, the gate terminal may be thought of as controlling the opening and closing of a physical gate. This gate permits electrons to flow through or blocks their passage by creating or eliminating a channel between the source and drain, electron-flow from the source terminal towards the drain terminal is influenced by an applied voltage. The body simply refers to the bulk of the semiconductor in which the gate, source, usually the body terminal is connected to the highest or lowest voltage within the circuit, depending on the type of the FET. The FET controls the flow of electrons from the source to drain by affecting the size and shape of a channel created and influenced by voltage applied across the gate
25.
Sample and hold
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Sample and hold circuits and related peak detectors are the elementary analog memory devices. They are typically used in converters to eliminate variations in input signal that can corrupt the conversion process. A typical sample and hold circuit stores electric charge in a capacitor and contains at least one switching device such as a FET switch, to sample the input signal the switch connects the capacitor to the output of a buffer amplifier. The buffer amplifier charges or discharges the capacitor so that the voltage across the capacitor is equal, or proportional to. In hold mode the switch disconnects the capacitor from the buffer, Sample and hold circuits are used in linear systems. In some kinds of analog-to-digital converters, the input is compared to a voltage generated internally from a digital-to-analog converter, the circuit tries a series of values and stops converting once the voltages are equal, within some defined error margin. If the input value was permitted to change during this comparison process, such successive approximation converters will often incorporate internal sample and hold circuitry. In addition, sample and hold circuits are used when multiple samples need to be measured at the same time. Each value is sampled and held, using a common sample clock, in order to maintain the level during a scanning cycle, an additional electric capacitor is attached in parallel to each LC pixel to better hold the voltage. A thin-film FET switch is addressed to select a particular LC pixel, in contrast to an S/H in general electronics, there is no output operational amplifier and no electrical signal AO. Instead, the charge on the hold capacitors controls the deformation of the LC molecules, the invention of this concept and its implementation in thin-film technology have been honored with the IEEE Jun-ichi Nishizawa Medal in 2011. During a scanning cycle, the picture doesn’t follow the input signal, Analog signal to discrete time interval converter Paul Horowitz, Winfield Hill. Analog Devices 21 page Tutorial Sample and Hold Amplifiers http, //www. analog. com/static/imported-files/tutorials/MT-090. pdf Ndjountche, CMOS Analog Integrated Circuits, High-Speed and Power-Efficient Design. Boca Raton, FL, USA, CRC Press, applications of Monolithic Sample and hold Amplifiers-Intersil
26.
Decibel
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The decibel is a logarithmic unit used to express the ratio of two values of a physical quantity. One of these values is often a reference value, in which case the decibel is used to express the level of the other value relative to this reference. When used in way, the decibel symbol is often qualified with a suffix that indicates the reference quantity that has been used or some other property of the quantity being measured. For example, dBm indicates a power of one milliwatt. There are two different scales used when expressing a ratio in decibels depending on the nature of the quantities, when expressing power quantities, the number of decibels is ten times the logarithm to base 10 of the ratio of two power quantities. That is, a change in power by a factor of 10 corresponds to a 10 dB change in level, when expressing field quantities, a change in amplitude by a factor of 10 corresponds to a 20 dB change in level. The difference in scales relates to the square law of fields in three-dimensional linear space. The decibel scales differ so that comparisons can be made between related power and field quantities when they are expressed in decibels. The definition of the decibel is based on the measurement of power in telephony of the early 20th century in the Bell System in the United States. One decibel is one tenth of one bel, named in honor of Alexander Graham Bell, however, today, the decibel is used for a wide variety of measurements in science and engineering, most prominently in acoustics, electronics, and control theory. In electronics, the gains of amplifiers, attenuation of signals, the decibel originates from methods used to quantify signal loss in telegraph and telephone circuits. The unit for loss was originally Miles of Standard Cable, the standard telephone cable implied was a cable having uniformly distributed resistance of 88 ohms per loop mile and uniformly distributed shunt capacitance of 0.054 microfarad per mile. 1 TU was defined such that the number of TUs was ten times the logarithm of the ratio of measured power to a reference power level. The definition was conveniently chosen such that 1 TU approximated 1 MSC, in 1928, the Bell system renamed the TU into the decibel, being one tenth of a newly defined unit for the base-10 logarithm of the power ratio. It was named the bel, in honor of the telecommunications pioneer Alexander Graham Bell, the bel is seldom used, as the decibel was the proposed working unit. However, the decibel is recognized by international bodies such as the International Electrotechnical Commission. The term field quantity is deprecated by ISO 80000-1, which favors root-power, in spite of their widespread use, suffixes are not recognized by the IEC or ISO. The ISO Standard 80000-3,2006 defines the following quantities, the decibel is one-tenth of a bel,1 dB =0.1 B
27.
Capacitance
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Capacitance is the ability of a body to store an electric charge. There are two related notions of capacitance--self capacitance and mutual capacitance--that are usually both designated by the same term, capacitance. Any object that can be electrically charged exhibits self capacitance, a material with a large self capacitance holds more electric charge at a given voltage, than one with low capacitance. The notion of mutual capacitance is important for understanding the operations of the capacitor. The capacitance is a function only of the geometry of the design, for many dielectric materials, the permittivity and thus the capacitance, is independent of the potential difference between the conductors and the total charge on them. The SI unit of capacitance is the farad, named after the English physicist Michael Faraday, a 1 farad capacitor, when charged with 1 coulomb of electrical charge, has a potential difference of 1 volt between its plates. In electrical circuits, the capacitance is usually a shorthand for the mutual capacitance between two adjacent conductors, such as the two plates of a capacitor. It is actually mutual capacitance between the turns of the coil and is a form of stray, or parasitic capacitance. This self-capacitance is an important consideration at high frequencies and it changes the impedance of the coil and gives rise to parallel resonance. In many applications this is an effect and sets an upper frequency limit for the correct operation of the circuit. The inverse of capacitance is called elastance, the unit of elastance is the daraf, but is not recognised by SI. A common form is a capacitor, which consists of two conductive plates insulated from each other, usually sandwiching a dielectric material. In a parallel capacitor, capacitance is very nearly proportional to the surface area of the conductor plates. If the charges on the plates are +q and −q, and V gives the voltage between the plates, then the capacitance C is given by C = q V. which gives the voltage/current relationship I = C d V d t. Historically, a farad was regarded as a large unit. Its subdivisions were invariably used, namely the microfarad, nanofarad and picofarad, more recently, technology has advanced such that capacitors of 1 farad and greater can be constructed in a structure little larger than a coin battery. Such capacitors are used for energy storage replacing more traditional batteries. The energy stored in a capacitor is found by integrating the work W, W charging =12 C V2 The discussion above is limited to the case of two conducting plates, although of arbitrary size and shape
28.
Frequency
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Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as frequency, which emphasizes the contrast to spatial frequency. The period is the duration of time of one cycle in a repeating event, for example, if a newborn babys heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as vibrations, audio signals, radio waves. For cyclical processes, such as rotation, oscillations, or waves, in physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter ν or ν. For a simple motion, the relation between the frequency and the period T is given by f =1 T. The SI unit of frequency is the hertz, named after the German physicist Heinrich Hertz, a previous name for this unit was cycles per second. The SI unit for period is the second, a traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. As a matter of convenience, longer and slower waves, such as ocean surface waves, short and fast waves, like audio and radio, are usually described by their frequency instead of period. Spatial frequency is analogous to temporal frequency, but the axis is replaced by one or more spatial displacement axes. Y = sin = sin d θ d x = k Wavenumber, in the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has a relationship to the wavelength. Even in dispersive media, the frequency f of a wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave. In the special case of electromagnetic waves moving through a vacuum, then v = c, where c is the speed of light in a vacuum, and this expression becomes, f = c λ. When waves from a monochrome source travel from one medium to another, their remains the same—only their wavelength. For example, if 71 events occur within 15 seconds the frequency is, the latter method introduces a random error into the count of between zero and one count, so on average half a count. This is called gating error and causes an error in the calculated frequency of Δf = 1/, or a fractional error of Δf / f = 1/ where Tm is the timing interval. This error decreases with frequency, so it is a problem at low frequencies where the number of counts N is small, an older method of measuring the frequency of rotating or vibrating objects is to use a stroboscope
29.
Duty cycle
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A duty cycle is the fraction of one period in which a signal or system is active. Duty cycle is expressed as a percentage or a ratio. A period is the time it takes for a signal to complete an on-and-off cycle, thus, a 60% duty cycle means the signal is on 60% of the time but off 40% of the time. The on time for a 60% duty cycle could be a fraction of a second, the duty factor for periodic signal expresses the same notion, but is usually scaled to a maximum of one rather than 100%. In electronics, duty cycle is the percentage of the ratio of pulse duration and it is generally used to represent time duration of a pulse when it is high. In digital electronics, signals are used in rectangular waveform which are represented by logic 1, logic 1 stands for presence of an electric pulse and 0 for absence of an electric pulse. For example, a signal has 50% duty cycle, because the pulse remains high for 1/2 of the period or low for 1/2 of the period. Similarly, for pulse the duty cycle will be 25% because the pulse remains high only for 1/4 of the period, electrical motors typically use less than a 100% duty cycle. For example, if a motor runs for one out of 100 seconds, or 1/100 of the time, then, its duty cycle is 1/100, pulse-width modulation is used in a variety of electronic situations, such as power delivery and voltage regulation. In electronic music, music synthesizers vary the duty cycle of their audio-frequency oscillators to obtain an effect on the tone colors. This technique is known as pulse-width modulation, in the printer / copier industry, the duty cycle specification refers to the rated throughput of a device per month. In a welding power supply, the duty cycle is defined as the percentage of time in a 10-minute period that it can be operated continuously before overheating. The concept of duty cycles is used to describe the activity of neurons. In a biological neural network for example, a duty cycle specifically refers to the proportion of a period in which a neuron remains active. One way to fairly accurate square wave signals with 1/n duty factor
30.
Buzzer
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A buzzer or beeper is an audio signaling device, which may be mechanical, electromechanical, or piezoelectric. Typical uses of buzzers and beepers include alarm devices, timers, the electric buzzer was invented in 1831 by Joseph Henry. They were mainly used in early doorbells until they were phased out in the early 1930s in favor of musical chimes, which had a softer tone. Piezoelectric buzzers, or piezo buzzers, as they are called, were invented by Japanese manufacturers. This advancement mainly came about because of efforts by Japanese manufacturing companies. Early devices were based on a system identical to an electric bell without the metal gong. Similarly, a relay may be connected to interrupt its own actuating current, often these units were anchored to a wall or ceiling to use it as a sounding board. The word buzzer comes from the noise that electromechanical buzzers made. A joy buzzer is an example of a purely mechanical buzzer, a piezoelectric element may be driven by an oscillating electronic circuit or other audio signal source, driven with a piezoelectric audio amplifier. Sounds commonly used to indicate that a button has been pressed are a click, while technological advancements have caused buzzers to be impractical and undesirable, there are still instances in which buzzers and similar circuits may be used
31.
Thermocouple
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A thermocouple is an electrical device consisting of two dissimilar conductors forming electrical junctions at differing temperatures. A thermocouple produces a temperature-dependent voltage as a result of the effect. Thermocouples are a widely used type of temperature sensor, commercial thermocouples are inexpensive, interchangeable, are supplied with standard connectors, and can measure a wide range of temperatures. In contrast to most other methods of measurement, thermocouples are self powered. The main limitation with thermocouples is accuracy, system errors of less than one degree Celsius can be difficult to achieve, Thermocouples are widely used in science and industry, applications include temperature measurement for kilns, gas turbine exhaust, diesel engines, and other industrial processes. Thermocouples are also used in homes, offices and businesses as the sensors in thermostats. At the time Seebeck referred to this as thermo-magnetism, the magnetic field he observed was later shown to be due to thermo-electric current. In practical use, the voltage generated at a junction of two different types of wire is what is of interest as this can be used to measure temperature at very high. The magnitude of the voltage depends on the types of wire used, generally, the voltage is in the microvolt range and care must be taken to obtain a usable measurement. Although current flows very little, power can be generated by a thermocouple junction. Power generation using multiple thermocouples, as in a thermopile, is common, the standard configuration for thermocouple usage is shown in the figure. Briefly, the desired temperature Tsense is obtained using three inputs—the characteristic function E of the thermocouple, the measured voltage V, and the reference junctions temperature Tref, the solution to the equation E = V + E yields Tsense. These details are hidden from the user since the reference junction block, voltmeter. The Seebeck effect refers to an electromotive force whenever there is a gradient in a conductive material. The standard measurement configuration shown in the figure, shows four temperature regions and thus four voltage contributions, Change from T m e t e r to T r e f, Change from T r e f to T s e n s e, in the alumel wire. Change from T s e n s e to T r e f, Change from T r e f to T m e t e r, in the upper copper wire. The first and fourth contributions cancel out exactly, because these regions involve the same temperature change, as a result, T m e t e r does not influence the measured voltage. The second and third contributions do not cancel, as they involve different materials, an integral does not need to be performed for every temperature measurement
32.
Inductance
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According to Lenzs law, a changing electric current through a circuit that contains inductance induces a proportional voltage, which opposes the change in current. The varying field in this circuit may also induce an EMF in neighbouring circuits, the term inductance was coined by Oliver Heaviside in 1886. It is customary to use the symbol L for inductance, in honour of the physicist Heinrich Lenz. In the SI system, the measurement unit for inductance is the henry, with the unit symbol H, named in honor of Joseph Henry, who discovered inductance independently of, an electronic component that is intended to add inductance to a circuit is called an inductor. Inductors are typically manufactured from coils of wire and this design delivers two desired properties, a concentration of the magnetic field into a small physical space and a linking of the magnetic field into the circuit multiple times. The relationship between the self-inductance, L, of a circuit, the voltage, v. A voltage is induced across an inductor, that is equal to the product of the inductors inductance, all circuits have, in practice, some inductance, which may have beneficial or detrimental effects. For a tuned circuit, inductance is used to provide a frequency-selective circuit, practical inductors may be used to provide filtering, or energy storage, in a given network. The inductance of long AC power transmission lines affects the power capacity of the line, sensitive circuits, such as microphone and computer network cables, may utilize special cabling construction, limiting the inductive coupling between circuits. The generalization to the case of K electrical circuits with currents, here, inductance L is a symmetric matrix. The diagonal coefficients Lm, m are called coefficients of self-inductance, the coefficients of inductance are constant, as long as no magnetizable material with nonlinear characteristics is involved. This is a consequence of the linearity of Maxwells equations in the fields. The coefficients of inductance become functions of the currents in the nonlinear case, the inductance equations above are a consequence of Maxwells equations. There is a derivation in the important case of electrical circuits consisting of thin wires. Here Nm denotes the number of turns in loop m, Φm, the flux through loop m. This equation follows from Amperes law - magnetic fields and fluxes are linear functions of the currents and this agrees with the definition of inductance above if the coefficients Lm, n are identified with the coefficients of inductance. Because the total currents Nnin contribute to Φm it also follows that Lm, ∑ n =1 K ∂ W ∂ i n d i n. This must agree with the change of the field energy, W
33.
Computer
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A computer is a device that can be instructed to carry out an arbitrary set of arithmetic or logical operations automatically. The ability of computers to follow a sequence of operations, called a program, such computers are used as control systems for a very wide variety of industrial and consumer devices. The Internet is run on computers and it millions of other computers. Since ancient times, simple manual devices like the abacus aided people in doing calculations, early in the Industrial Revolution, some mechanical devices were built to automate long tedious tasks, such as guiding patterns for looms. More sophisticated electrical machines did specialized analog calculations in the early 20th century, the first digital electronic calculating machines were developed during World War II. The speed, power, and versatility of computers has increased continuously and dramatically since then, conventionally, a modern computer consists of at least one processing element, typically a central processing unit, and some form of memory. The processing element carries out arithmetic and logical operations, and a sequencing, peripheral devices include input devices, output devices, and input/output devices that perform both functions. Peripheral devices allow information to be retrieved from an external source and this usage of the term referred to a person who carried out calculations or computations. The word continued with the same meaning until the middle of the 20th century, from the end of the 19th century the word began to take on its more familiar meaning, a machine that carries out computations. The Online Etymology Dictionary gives the first attested use of computer in the 1640s, one who calculates, the Online Etymology Dictionary states that the use of the term to mean calculating machine is from 1897. The Online Etymology Dictionary indicates that the use of the term. 1945 under this name, theoretical from 1937, as Turing machine, devices have been used to aid computation for thousands of years, mostly using one-to-one correspondence with fingers. The earliest counting device was probably a form of tally stick, later record keeping aids throughout the Fertile Crescent included calculi which represented counts of items, probably livestock or grains, sealed in hollow unbaked clay containers. The use of counting rods is one example, the abacus was initially used for arithmetic tasks. The Roman abacus was developed from used in Babylonia as early as 2400 BC. Since then, many forms of reckoning boards or tables have been invented. In a medieval European counting house, a checkered cloth would be placed on a table, the Antikythera mechanism is believed to be the earliest mechanical analog computer, according to Derek J. de Solla Price. It was designed to calculate astronomical positions and it was discovered in 1901 in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, and has been dated to circa 100 BC
34.
Ammeter
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An ammeter is a measuring instrument used to measure the current in a circuit. Electric currents are measured in amperes, hence the name, instruments used to measure smaller currents, in the milliampere or microampere range, are designated as milliammeters or microammeters. Early ammeters were laboratory instruments which relied on the Earths magnetic field for operation, by the late 19th century, improved instruments were designed which could be mounted in any position and allowed accurate measurements in electric power systems. The tangent galvanometer was used to measure using this effect. This made these instruments usable only when aligned with the Earths field, sensitivity of the instrument was increased by using additional turns of wire to multiply the effect – the instruments were called multipliers. The DArsonval galvanometer is a moving coil ammeter and it uses magnetic deflection, where current passing through a coil placed in the magnetic field of a permanent magnet causes the coil to move. The modern form of instrument was developed by Edward Weston. The uniform air gap between the core and the permanent magnet poles make the deflection of the meter linearly proportional to current. Basic meter movements can have full-scale deflection for currents from about 25 microamperes to 10 milliamperes, because the magnetic field is polarised, the meter needle acts in opposite directions for each direction of current. A DC ammeter is thus sensitive to which way round it is connected, most are marked with a positive terminal, a moving coil meter indicates the average of a varying current through it, which is zero for AC. For this reason moving-coil meters are only usable directly for DC and this type of meter movement is extremely common for both ammeters and other meters derived from them, such as voltmeters and ohmmeters. Moving magnet ammeters operate on essentially the same principle as moving coil, except that the coil is mounted in the case. Indeed, some Ammeters of this type do not have hairsprings at all, an electrodynamic movement uses an electromagnet instead of the permanent magnet of the dArsonval movement. This instrument can respond to both alternating and direct current and also indicates true RMS for AC, see Wattmeter for an alternative use for this instrument. Moving iron ammeters use a piece of iron which moves when acted upon by the force of a fixed coil of wire. The moving-iron meter was invented by Austrian engineer Friedrich Drexler in 1884 and this type of meter responds to both direct and alternating currents. The iron element consists of a vane attached to a pointer. The deflection of a moving iron meter is proportional to the square of the current, consequently, such meters would normally have a non linear scale, but the iron parts are usually modified in shape to make the scale fairly linear over most of its range
35.
Ohmmeter
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An ohmmeter is an electrical instrument that measures electrical resistance, the opposition to an electric current. Megohmmeters measure large values of resistance, the unit of measurement for resistance is ohms. The first ohmmeters were based on a type of movement known as a ratiometer. These were similar to the galvanometer type movement encountered in later instruments and these provided no net rotational force to the movement. Also, the movement was wound with two coils, one was connected via a series resistor to the battery supply. The second was connected to the battery supply via a second resistor. The indication on the meter was proportional to the ratio of the currents through the two coils and this ratio was determined by the magnitude of the resistor under test. The advantages of this arrangement were twofold, first, the indication of the resistance was completely independent of the battery voltage and no zero adjustment was required. Second, although the scale was non linear, the scale remained correct over the full deflection range. By interchanging the two coils a second range was provided and this scale was reversed compared to the first. A feature of type of instrument was that it would continue to indicate a random resistance value once the test leads were disconnected. Ohmmeters of this only ever measured resistance as they could not easily be incorporated into a multimeter design. Insulation testers that relied on a hand cranked generator operated on the same principle and this ensured that the indication was wholly independent of the voltage actually produced. Subsequent designs of ohmmeter provided a battery to apply a voltage to a resistance via a galvanometer to measure the current through the resistance. The scale of the galvanometer was marked in ohms, because the voltage from the battery assured that as resistance is decreased. Ohmmeters form circuits by themselves, therefore they cannot be used within an assembled circuit and this design is much simpler and cheaper than the former design, and was simple to integrate into a multimeter design and consequently was by far the most common form of analogue ohmmeter. This type of ohmmeter suffers two inherent disadvantages, first, the meter needs to be zeroed by shorting the measurement points together and performing an adjustment for zero ohms indication prior to each measurement. This is because as the voltage decreases with age, the series resistance in the meter needs to be reduced to maintain the zero indication at full deflection
36.
Shunt (electrical)
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In electronics, a shunt is a device which allows electric current to pass around another point in the circuit by creating a low resistance path. The term is widely used in photovoltaics to describe an unwanted short circuit between the front and back surface contacts of a solar cell, usually caused by wafer damage. The origin of the term is in the verb to shunt meaning to turn away or follow a different path, one example is in miniature Christmas lights which are wired in series. When the filament burns out in one of the incandescent light bulbs, the much higher voltage that this creates causes the shunt to short out and become part of the circuit, again allowing electricity to pass and the set to light. If too many lights burn out however, a shunt will also burn out, a gas-filled tube can also be used as a shunt, particularly in a lightning arrestor. Neon and other noble gases have a breakdown voltage, so that normally current will not flow across it. However, a lightning strike will cause the shunt to arc and conduct the massive amount of electricity to ground, protecting transmitters. Another older form of lightning arrestor employs a simple spark gap. While this is a low cost solution, its triggering voltage offers almost no protection for modern solid-state electronic devices powered by the protected circuit. Capacitors are used as shunts to redirect high-frequency noise to ground before it can propagate to the load or other circuit components, the term shunt is used in filter and similar circuits with a ladder topology to refer to the components connected between the line and common. The term is used in context to distinguish the shunt components connected between the signal and return lines from the components connected in series along the signal line. More generally, the shunt can be used for a component connected in parallel with another. For instance, shunt m-derived half section is a filter section from the image impedance method of filter design. Where devices are sensitive to reverse polarity of signal or power supply. If connected in series with the circuit it simply prevents reversed current, all diodes have a trigger voltage – typically between ½ Volt and 1 Volt – that must be exceeded before current will flow through the diode in the normally allowed direction. Two anti-parallel shunt diodes can be used to limit the power of a signal flowing past them to no more than their trigger voltage, when this device detects an overvoltage it causes a short circuit between the power supply and its return. This will cause both a drop in voltage and an instantaneous high current which is expected to open a current sensitive device. This device is called a crowbar as it is likened to dropping an actual crowbar across a set of bus bars, an ammeter shunt allows the measurement of current values too large to be directly measured by a particular ammeter
37.
Rectifier
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A rectifier is an electrical device that converts alternating current, which periodically reverses direction, to direct current, which flows in only one direction. The process is known as rectification, historically, even synchronous electromechanical switches and motors have been used. Early radio receivers, called crystal radios, used a cats whisker of fine wire pressing on a crystal of galena to serve as a rectifier or crystal detector. Rectifiers have many uses, but are found serving as components of DC power supplies. Rectification may serve in other than to generate direct current for use as a source of power. As noted, detectors of radio signals serve as rectifiers, in gas heating systems flame rectification is used to detect presence of a flame. Because of the nature of the input AC sine wave. Many applications of rectifiers, such as supplies for radio, television and computer equipment. In these applications the output of the rectifier is smoothed by a filter to produce a steady current. More complex circuitry that performs the function, converting DC to AC, is called an inverter. Before the development of semiconductor rectifiers, vacuum tube thermionic diodes. With the introduction of electronics, vacuum tube rectifiers became obsolete. For power rectification from very low to high current, semiconductor diodes of various types are widely used. Other devices that have control electrodes as well as acting as unidirectional current valves are used more than simple rectification is required—e. g. Where variable output voltage is needed, high-power rectifiers, such as those used in high-voltage direct current power transmission, employ silicon semiconductor devices of various types. These are thyristors or other controlled switching solid-state switches, which function as diodes to pass current in only one direction. Rectifier circuits may be single-phase or multi-phase, most low power rectifiers for domestic equipment are single-phase, but three-phase rectification is very important for industrial applications and for the transmission of energy as DC. Because only one half of the input waveform reaches the output, half-wave rectification requires a single diode in a single-phase supply, or three in a three-phase supply
38.
Root mean square
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In statistics and its applications, the root mean square is defined as the square root of mean square. The RMS is also known as the mean and is a particular case of the generalized mean with exponent 2. RMS can also be defined for a continuously varying function in terms of an integral of the squares of the values during a cycle. For a cyclically alternating electric current, RMS is equal to the value of the current that would produce the same average power dissipation in a resistive load. In Estimation theory the mean square error of an estimator is a measure of the imperfection of the fit of the estimator to the data. The RMS value of a set of values is the root of the arithmetic mean of the squares of the values. In Physics, the RMS current is the value of the current that dissipates power in a resistor. In the case of a set of n values, the RMS x r m s =1 n, the RMS over all time of a periodic function is equal to the RMS of one period of the function. The RMS value of a function or signal can be approximated by taking the RMS of a sequence of equally spaced samples. Additionally, the RMS value of various waveforms can also be determined without calculus, in the case of the RMS statistic of a random process, the expected value is used instead of the mean. If the waveform is a sine wave, the relationships between amplitudes and RMS are fixed and known, as they are for any continuous periodic wave. However, this is not true for a waveform which may or may not be periodic or continuous. For a zero-mean sine wave, the relationship between RMS and peak-to-peak amplitude is, Peak-to-peak =22 × R M S ≈2.8 × R M S, for other waveforms the relationships are not the same as they are for sine waves. Waveforms made by summing known simple waveforms have an RMS that is the root of the sum of squares of the component RMS values, if the component waveforms are orthogonal. R M S Total = R M S12 + R M S22 + ⋯ + R M S n 2 A special case of this, another special case, useful in statistics, is given in #Relationship to other statistics. Electrical engineers often need to know the power, P, dissipated by an electrical resistance and it is easy to do the calculation when there is a constant current, I, through the resistance. Average power can also be using the same method that in the case of a time-varying voltage, V, with RMS value VRMS. This equation can be used for any waveform, such as a sinusoidal or sawtooth waveform
39.
Voltage divider
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In electronics, a voltage divider is a passive linear circuit that produces an output voltage that is a fraction of its input voltage. Voltage division is the result of distributing the input voltage among the components of the divider, a simple example of a voltage divider is two resistors connected in series, with the input voltage applied across the resistor pair and the output voltage emerging from the connection between them. Resistor voltage dividers are used to create reference voltages, or to reduce the magnitude of a voltage so it can be measured. In electric power transmission, a voltage divider is used for measurement of high voltage. A voltage divider referenced to ground is created by connecting two electrical impedances in series, as shown in Figure 1, the input voltage is applied across the series impedances Z1 and Z2 and the output is the voltage across Z2. Z1 and Z2 may be composed of any combination of such as resistors, inductors and capacitors. A resistive divider is the case where both impedances, Z1 and Z2, are purely resistive and that is, using resistors alone it is not possible to either invert the voltage or increase Vout above Vin. Consider a divider consisting of a resistor and capacitor as shown in Figure 3, the product τ = RC is called the time constant of the circuit. The ratio then depends on frequency, in this case decreasing as frequency increases and this circuit is, in fact, a basic lowpass filter. The ratio contains a number, and actually contains both the amplitude and phase shift information of the filter. To extract just the amplitude ratio, calculate the magnitude of the ratio, that is, | V o u t V i n | =11 +2. Inductive dividers split AC input according to inductance, V o u t = L2 L1 + L2 ⋅ V i n The above equation is for non-interacting inductors, inductive dividers split DC input according to the resistance of the elements as for the resistive divider above. Capacitive dividers do not pass DC input, for an AC input a simple capacitive equation is, V o u t = C1 C1 + C2 ⋅ V i n Any leakage current in the capactive elements requires use of the generalized expression with two impedances. By selection of parallel R and C elements in the proper proportions and this is the principle applied in compensated oscilloscope probes to increase measurement bandwidth. The output voltage of a voltage divider will vary according to the current it is supplying to its external electrical load. The effective source impedance coming from a divider of Z1 and Z2, as above, will be Z1 in parallel with Z2, to obtain a sufficiently stable output voltage, the output current must either be stable or limited to an appropriately small percentage of the dividers input current. Voltage regulators are used in lieu of passive voltage dividers when it is necessary to accommodate high or fluctuating load currents. Voltage dividers are used for adjusting the level of a signal, for bias of active devices in amplifiers, a Wheatstone bridge and a multimeter both include voltage dividers
40.
Current clamp
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In electrical and electronic engineering, a current clamp or current probe is an electrical device having jaws which open to allow clamping around an electrical conductor. This allows measurement of the current in a conductor without the need to make contact with it. Current clamps are used to read the magnitude of alternating current and, with additional instrumentation. Some clamps meters can measure currents of 1000 A and more, Hall effect and vane type clamps can also measure direct current. A common form of current clamp comprises a ring made of ferrite or soft iron. A wire coil is wound round one or both halves, forming one winding of a current transformer, the conductor around which it is clamped forms the other winding. Like any transformer this type works only with AC or pulse waveforms, when measuring current, the subject conductor forms the primary winding and the coil forms the secondary. This type may also be used in reverse, to inject current into the conductor, for example in electromagnetic compatibility susceptibility testing to induce an interference current, usually, the injection probe is specifically designed for this purpose. In this mode, the forms the primary and the test conductor the secondary. Due to its size it is generally limited to power transmission frequencies up to around 100 Hz. The vane is usually fixed directly to the mechanism of an analogue clamp meter. The Hall effect type is sensitive and is able to measure both DC and AC, in some examples up to the kilohertz range. This type was used with oscilloscopes, and with high-end computerized digital multimeters, however. Resembling a current clamp in appearance and function is the Rogowski coil current sensor and this coreless transformer is used in clamp meters and power monitoring loggers. It has the advantage of better linearity, having no core to saturate, it can be made flexible, and does not require any magnetic or electrical contact at the opening end. The Rogowski coil gives a proportional to the rate of change of current in the primary cable. An electrical meter with integral AC current clamp is known as a clamp meter, a clamp meter measures the vector sum of the currents flowing in all the conductors passing through the probe, which depends on the phase relationship of the currents. Only one conductor is passed through the probe
41.
Alternating current
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Alternating current, is an electric current which periodically reverses direction, whereas direct current flows only in one direction. A common source of DC power is a cell in a flashlight. The abbreviations AC and DC are often used to mean simply alternating and direct, the usual waveform of alternating current in most electric power circuits is a sine wave. In certain applications, different waveforms are used, such as triangular or square waves, audio and radio signals carried on electrical wires are also examples of alternating current. These types of alternating current carry information encoded onto the AC signal and these currents typically alternate at higher frequencies than those used in power transmission. Electrical energy is distributed as alternating current because AC voltage may be increased or decreased with a transformer, use of a higher voltage leads to significantly more efficient transmission of power. The power losses in a conductor are a product of the square of the current and this means that when transmitting a fixed power on a given wire, if the current is halved, the power loss will be four times less. Power is often transmitted at hundreds of kilovolts, and transformed to 100–240 volts for domestic use, high voltages have disadvantages, such as the increased insulation required, and generally increased difficulty in their safe handling. In a power plant, energy is generated at a convenient voltage for the design of a generator, near the loads, the transmission voltage is stepped down to the voltages used by equipment. Consumer voltages vary somewhat depending on the country and size of load, the voltage delivered to equipment such as lighting and motor loads is standardized, with an allowable range of voltage over which equipment is expected to operate. Standard power utilization voltages and percentage tolerance vary in the different mains power systems found in the world, high-voltage direct-current electric power transmission systems have become more viable as technology has provided efficient means of changing the voltage of DC power. HVDC systems, however, tend to be expensive and less efficient over shorter distances than transformers. Three-phase electrical generation is very common, the simplest way is to use three separate coils in the generator stator, physically offset by an angle of 120° to each other. Three current waveforms are produced that are equal in magnitude and 120° out of phase to each other, if coils are added opposite to these, they generate the same phases with reverse polarity and so can be simply wired together. In practice, higher pole orders are commonly used, for example, a 12-pole machine would have 36 coils. The advantage is that lower rotational speeds can be used to generate the same frequency, for example, a 2-pole machine running at 3600 rpm and a 12-pole machine running at 600 rpm produce the same frequency, the lower speed is preferable for larger machines. If the load on a system is balanced equally among the phases. Even in the worst-case unbalanced load, the current will not exceed the highest of the phase currents
42.
Direct current
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Direct current is a flow of electrical charge carriers that always takes place in the same direction. The current need not always have the magnitude, but if it is to be defined as dc. This contrasts with alternating current which varies the direction of flow, sources of direct current include power supplies, electrochemical cells and batteries, and photovoltaic cells and panels. The intensity, or amplitude, of a direct current might fluctuate with time, in some such cases the dc has an ac component superimposed on it. An example of this is the output of a cell that receives a modulated light communications signal. A source of dc is sometimes called a dc generator, batteries and various other sources of dc produce a constant voltage. This is called pure dc and can be represented by a straight, the peak and effective values are the same. The peak to peak value is zero because the instantaneous amplitude never changes, in some instances the value of a dc voltage pulsates or oscillates rapidly with time, in a manner similar to the changes in an ac wave. The unfiltered output of a wave or a full wave rectifier. In 1820, Hans Christian Orsted discovered that electrical current creates a magnetic field and this discovery made scientists relate magnetism to the electric phenomena. In 1879, Thomas Edison invented the light bulb. He improved a 50-year-old idea using lower current electricity, a vacuum inside the globe and a small carbonized filament. At that time, the idea of lightning was not new. Edison not only invented an incandescent electric light, but an electric lighting system contained all the necessary elements to make the incandescent light safe, economical. Prior to 1879, direct current electricity had been used in lighting for the outdoors and it was in the 1880s when the modern electric utility industry began. It was an evolution from street lighting systems and from gas and it was located in Lower Manhattan, on Pearl Street. This station provided light and electricity to customers in a one square mile range, the station was called Thomas Edisons Pearl Street Electricity Generating Station. This station introduced four elements of an electric utility system, Efficient distribution, competitive price, reliable central generation
43.
Volt
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The volt is the derived unit for electric potential, electric potential difference, and electromotive force. One volt is defined as the difference in potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points. It is also equal to the difference between two parallel, infinite planes spaced 1 meter apart that create an electric field of 1 newton per coulomb. Additionally, it is the difference between two points that will impart one joule of energy per coulomb of charge that passes through it. It can also be expressed as amperes times ohms, watts per ampere, or joules per coulomb, for the Josephson constant, KJ = 2e/h, the conventional value KJ-90 is used, K J-90 =0.4835979 GHz μ V. This standard is typically realized using an array of several thousand or tens of thousands of junctions. Empirically, several experiments have shown that the method is independent of device design, material, measurement setup, etc. in the water-flow analogy sometimes used to explain electric circuits by comparing them with water-filled pipes, voltage is likened to difference in water pressure. Current is proportional to the diameter of the pipe or the amount of water flowing at that pressure. A resistor would be a reduced diameter somewhere in the piping, the relationship between voltage and current is defined by Ohms Law. Ohms Law is analogous to the Hagen–Poiseuille equation, as both are linear models relating flux and potential in their respective systems, the voltage produced by each electrochemical cell in a battery is determined by the chemistry of that cell. Cells can be combined in series for multiples of that voltage, mechanical generators can usually be constructed to any voltage in a range of feasibility. High-voltage electric power lines,110 kV and up Lightning, Varies greatly. Volta had determined that the most effective pair of metals to produce electricity was zinc. In 1861, Latimer Clark and Sir Charles Bright coined the name volt for the unit of resistance, by 1873, the British Association for the Advancement of Science had defined the volt, ohm, and farad. In 1881, the International Electrical Congress, now the International Electrotechnical Commission and they made the volt equal to 108 cgs units of voltage, the cgs system at the time being the customary system of units in science. At that time, the volt was defined as the difference across a conductor when a current of one ampere dissipates one watt of power. The international volt was defined in 1893 as 1/1.434 of the emf of a Clark cell and this definition was abandoned in 1908 in favor of a definition based on the international ohm and international ampere until the entire set of reproducible units was abandoned in 1948. Prior to the development of the Josephson junction voltage standard, the volt was maintained in laboratories using specially constructed batteries called standard cells
44.
Capacitor
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A capacitor is a passive two-terminal electrical component that stores electrical energy in an electric field. The effect of a capacitor is known as capacitance, a capacitor was therefore historically first known as an electric condenser. The physical form and construction of practical capacitors vary widely and many types are in common use. Most capacitors contain at least two electrical conductors often in the form of plates or surfaces separated by a dielectric medium. A conductor may be a foil, thin film, sintered bead of metal, the nonconducting dielectric acts to increase the capacitors charge capacity. Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, mica, Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, a capacitor does not dissipate energy. No current actually flows through the dielectric, instead, the effect is a displacement of charges through the source circuit, if the condition is maintained sufficiently long, this displacement current through the battery ceases. However, if a voltage is applied across the leads of the capacitor. Capacitance is defined as the ratio of the charge on each conductor to the potential difference between them. The unit of capacitance in the International System of Units is the farad, capacitance values of typical capacitors for use in general electronics range from about 1 pF to about 1 mF. The capacitance of a capacitor is proportional to the area of the plates. In practice, the dielectric between the plates passes a small amount of leakage current and it has an electric field strength limit, known as the breakdown voltage. The conductors and leads introduce an undesired inductance and resistance, Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. In analog filter networks, they smooth the output of power supplies, in resonant circuits they tune radios to particular frequencies. In electric power systems, they stabilize voltage and power flow. The property of energy storage in capacitors was exploited as dynamic memory in digital computers. Von Kleists hand and the water acted as conductors, and the jar as a dielectric, von Kleist found that touching the wire resulted in a powerful spark, much more painful than that obtained from an electrostatic machine
45.
Farad
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The farad is the SI derived unit of electrical capacitance, the ability of a body to store an electrical charge. It is named after the English physicist Michael Faraday, one farad is defined as the capacitance across which, when charged with one coulomb, there is a potential difference of one volt. Equally, one farad can be described as the capacitance which stores a one-coulomb charge across a potential difference of one volt, the relationship between capacitance, charge and potential difference is linear. For example, if the difference across a capacitor is halved. For most applications, the farad is a large unit of capacitance. Most electrical and electronic applications are covered by the following SI prefixes,1 mF =1000 μF =1000000 nF1 μF =0.000001 F =1000 nF =1000000 pF1 nF =0. In 1881 at the International Congress of Electricians in Paris, the name farad was officially used for the unit of electrical capacitance, a capacitor consists of two conducting surfaces, frequently referred to as plates, separated by an insulating layer usually referred to as a dielectric. The original capacitor was the Leyden jar developed in the 18th century and it is the accumulation of electric charge on the plates that results in capacitance. Values of capacitors are specified in farads, microfarads, nanofarads and picofarads. The millifarad is rarely used in practice, while the nanofarad is uncommon in North America, the size of commercially available capacitors ranges from around 0.1 pF to 5000F supercapacitors. Capacitance values of 1 pF or lower can be achieved by twisting two short lengths of insulated wire together, the capacitance of the Earths ionosphere with respect to the ground is calculated to be about 1 F. The picofarad is sometimes pronounced as puff or pic, as in a ten-puff capacitor. Similarly, mic is sometimes used informally to signify microfarads, if the Greek letter μ is not available, the notation uF is often used as a substitute for μF in electronics literature. A micro-microfarad, an obsolete unit sometimes found in texts, is the equivalent of a picofarad. In texts prior to 1960, and on capacitor packages even more recently. Similarly, mmf or MMFD represented picofarads, the reciprocal of capacitance is called electrical elastance, the unit of which is the daraf. The abfarad is an obsolete CGS unit of equal to 109 farads. The statfarad is a rarely used CGS unit equivalent to the capacitance of a capacitor with a charge of 1 statcoulomb across a potential difference of 1 statvolt and it is 1/ farad, approximately 1.1126 picofarads
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Dissipation factor
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In physics, the dissipation factor is a measure of loss-rate of energy of a mode of oscillation in a dissipative system. It is the reciprocal of quality factor, which represents the quality or durability of oscillation, electrical potential energy is dissipated in all dielectric materials, usually in the form of heat. The ESR represents losses in the capacitor, in a good capacitor the ESR is very small, and in a poor capacitor the ESR is large. However, ESR is sometimes a minimum value to be required, note that the ESR is not simply the resistance that would be measured across a capacitor by an ohmmeter. The ESR is a quantity with physical origins in both the dielectrics conduction electrons and dipole relaxation phenomena. In dielectric only one of either the conduction electrons or the dipole relaxation typically dominates loss, DF approximates to the power factor when ESR is far less than X c, which is usually the case. DF will vary depending on the material and the frequency of the electrical signals. In low dielectric constant, temperature compensating ceramics, DF of 0. 1% to 0. 2% is typical, in high dielectric constant ceramics, DF can be 1% to 2%. However, lower DF is usually an indication of quality capacitors when comparing similar dielectric material
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Electrical resistance and conductance
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The electrical resistance of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor. The inverse quantity is electrical conductance, and is the ease with which a current passes. Electrical resistance shares some parallels with the notion of mechanical friction. The SI unit of resistance is the ohm, while electrical conductance is measured in siemens. An object of uniform cross section has a proportional to its resistivity and length. All materials show some resistance, except for superconductors, which have a resistance of zero and this proportionality is called Ohms law, and materials that satisfy it are called ohmic materials. In other cases, such as a diode or battery, V and I are not directly proportional. The ratio V/I is sometimes useful, and is referred to as a chordal resistance or static resistance, since it corresponds to the inverse slope of a chord between the origin and an I–V curve. In other situations, the derivative d V d I may be most useful, in the hydraulic analogy, current flowing through a wire is like water flowing through a pipe, and the voltage drop across the wire is like the pressure drop that pushes water through the pipe. Conductance is proportional to how much flow occurs for a given pressure, the voltage drop, not the voltage itself, provides the driving force pushing current through a resistor. In hydraulics, it is similar, The pressure difference between two sides of a pipe, not the pressure itself, determines the flow through it, for example, there may be a large water pressure above the pipe, which tries to push water down through the pipe. But there may be a large water pressure below the pipe. If these pressures are equal, no water flows, in the same way, a long, thin copper wire has higher resistance than a short, thick copper wire. A pipe filled with hair restricts the flow of more than a clean pipe of the same shape. The difference between copper, steel, and rubber is related to their structure and electron configuration. In addition to geometry and material, there are other factors that influence resistance and conductance, such as temperature. Substances in which electricity can flow are called conductors, a piece of conducting material of a particular resistance meant for use in a circuit is called a resistor. Conductors are made of high-conductivity materials such as metals, in particular copper, Resistors, on the other hand, are made of a wide variety of materials depending on factors such as the desired resistance, amount of energy that it needs to dissipate, precision, and costs
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