1.
Active current loop
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In electrical signalling an analog current loop is used where a device must be monitored or controlled remotely over a pair of conductors. Only one current level can be present at any time and they are also used to transmit controller outputs to the modulating field devices such as control valves. These loops have the advantages of simplicity and noise immunity, and have an international user. Various Automation Protocols may replace analog current loops, but 4-20 mA is still an industrial standard. In industrial process control, analog 4–20 mA current loops are used for electronic signalling. These loops are used both for carrying information from field instrumentation, and carrying control signals to the process modulating devices. The key advantages of the current loop are, The loop can often power the device, with power supplied by the controller. Many instrumentation manufacturers produce 4-20 mA sensors which are loop powered, the live or elevated zero of 4 mA allows powering of the device even with no process signal output from the field transmitter. The accuracy of the signal is not affected by voltage drop in the interconnecting wiring and it has high noise immunity as it is low impedance circuit usually through twisted pair conductors. It is self-monitoring, currents less than 3.8 mA or more than 20.5 mA are taken to indicate a fault and it can be carried over long cables up to the limit of the resistance for the voltage used. In line displays can be inserted and powered by the loop, easy conversion to voltage using a resistor. Loop powered I to P converters can convert the 4-20 mA signal to a 3-15 psi pneumatic output for control valves, field instrumentation measurements are such as pressure, temperature, level, flow, pH or other process variables. A current loop can also be used to control a valve positioner or other output actuator, since input terminals of instruments may have one side of the current loop input tied to the chassis ground, analog isolators may be required when connecting several instruments in series. The relationship between current value and process variable measurement is set by calibration, which assigns different ranges of engineering units to the span between 4 and 20 mA. The mapping between engineering units and current can be inverted, so that 4 mA represents the maximum and 20 mA the minimum, depending on the source of current for the loop, devices may be classified as active or passive. For example, a chart recorder may provide power to a pressure transmitter. The pressure transmitter modulates the current on the loop to send the signal to the strip chart recorder, another loop may contain two passive chart recorders, a passive pressure transmitter, and a 24 V battery. Note that a 4-wire instrument has a power supply separate from the current loop
Active current loop
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Typ 2
2.
Icl 7107
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In electronics, an analog-to-digital converter is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. Typically the digital output is a twos complement binary number that is proportional to the input, due to the complexity and the need for precisely matched components, all but the most specialized ADCs are implemented as integrated circuits. A digital-to-analog converter performs the function, it converts a digital signal into an analog signal. The conversion involves quantization of the input, so it necessarily introduces a small amount of error, furthermore, instead of continuously performing the conversion, an ADC does the conversion periodically, sampling the input. The result is a sequence of values that have been converted from a continuous-time and continuous-amplitude analog signal to a discrete-time. An ADC is defined by its bandwidth and its signal-to-noise ratio, the bandwidth of an ADC is characterized primarily by its sampling rate. The dynamic range of an ADC is influenced by many factors, including the resolution, linearity and accuracy, aliasing and jitter. The dynamic range of an ADC is often summarized in terms of its number of bits. An ideal ADC has an ENOB equal to its resolution, ADCs are chosen to match the bandwidth and required signal-to-noise ratio of the signal to be quantized. If an ADC operates at a rate greater than twice the bandwidth of the signal, then perfect reconstruction is possible given an ideal ADC. The presence of quantization error limits the range of even an ideal ADC. However, if the range of the ADC exceeds that of the input signal. The resolution of the converter indicates the number of values it can produce over the range of analog values. The resolution determines the magnitude of the error and therefore determines the maximum possible average signal to noise ratio for an ideal ADC without the use of oversampling. The values are stored electronically in binary form, so the resolution is usually expressed in bits. In consequence, the number of discrete values available, or levels, is assumed to be a power of two, for example, an ADC with a resolution of 8 bits can encode an analog input to one in 256 different levels, since 28 =256. The values can represent the ranges from 0 to 255 or from −128 to 127, resolution can also be defined electrically, and expressed in volts. The minimum change in required to guarantee a change in the output code level is called the least significant bit voltage
Icl 7107
–
4-channel stereo multiplexed analog-to-digital converter WM8775SEDS made by
Wolfson Microelectronics placed on an
X-Fi Fatal1ty Pro sound card.
3.
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
Wheatstone bridge
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Wheatstone bridge
circuit diagram.
4.
Centrifical pump
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Centrifugal pumps are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. Centrifugal pumps are used to transport fluids by the conversion of kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor, the fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber, from where it exits. Common uses include water, sewage, petroleum and petrochemical pumping, the reverse function of the centrifugal pump is a water turbine converting potential energy of water pressure into mechanical rotational energy. True centrifugal pumps were not developed until the late 17th century, the curved vane was introduced by British inventor John Appold in 1851. Like most pumps, a centrifugal pump converts rotational energy, often from a motor, a portion of the energy goes into kinetic energy of the fluid. The fluid gains both velocity and pressure while passing through the impeller, the doughnut-shaped diffuser, or scroll, section of the casing decelerates the flow and further increases the pressure. A consequence of Newton’s second law of mechanics is the conservation of the momentum which is of fundamental significance to all turbomachines. Accordingly, the change of the momentum is equal to the sum of the external moments. Angular momentums ρ×Q×r×cu at inlet and outlet, an external torque M and this is an important role in old academic, this rule was helpful to detail Eq. become Eq. and wide explained how the pump works. Fig 2.3 shows triangle velocity of forward curved vanes impeller and it illustrates rather clearly energy added to the flow inversely change upon flow rate Q. Power is more commonly expressed as kilowatts or horsepower, the value for the pump efficiency, η p u m p, may be stated for the pump itself or as a combined efficiency of the pump and motor system. Vertical centrifugal pumps are also referred to as cantilever pumps and they utilize a unique shaft and bearing support configuration that allows the volute to hang in the sump while the bearings are outside the sump. This style of pump uses no stuffing box to seal the shaft, a common application for this style of pump is in a parts washer. In the mineral industry, or in the extraction of oilsand, froth is generated to separate the rich minerals or bitumen from the sand, froth contains air that tends to block conventional pumps and cause loss of prime. Over history, industry has developed different ways to deal with this problem, in the pulp and paper industry holes are drilled in the impeller. Air escapes to the back of the impeller and a special expeller discharges the air back to the suction tank, the impeller may also feature special small vanes between the primary vanes called split vanes or secondary vanes. Some pumps may feature an eye, an inducer or recirculation of pressurized froth from the pump discharge back to the suction to break the bubbles
Centrifical pump
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Warman centrifugal pump in a
coal preparation plant application
Centrifical pump
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Figure 2.2 -- triangle velocity of a curved backward vanes impeller (a).
Centrifical pump
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Figure 2.2 -- triangle velocity of a radial straight vanes impeller (b).
Centrifical pump
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Multistage centrifugal pump
5.
Digital works
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The word digital comes from the same source as the words digit and digitus, as fingers are often used for discrete counting. Mathematician George Stibitz of Bell Telephone Laboratories used the word digital in reference to the fast electric pulses emitted by a device designed to aim and fire anti-aircraft guns in 1942. The term is most commonly used in computing and electronics, especially where real-world information is converted to binary numeric form as in digital audio, since symbols are not continuous, representing symbols digitally is rather simpler than conversion of continuous or analog information to digital. Instead of sampling and quantization as in analog-to-digital conversion, such techniques as polling and encoding are used, a symbol input device usually consists of a group of switches that are polled at regular intervals to see which switches are switched. Data will be lost if, within a single polling interval and this polling can be done by a specialized processor in the device to prevent burdening the main CPU. When a new symbol has been entered, the device sends a interrupt, in a specialized format. For devices with only a few switches, the status of each can be encoded as bits in a single word and this is useful when combinations of key presses are meaningful, and is sometimes used for passing the status of modifier keys on a keyboard. But it does not scale to support more keys than the number of bits in a byte or word. Devices with many switches usually arrange these switches in a scan matrix, when a switch is pressed, it connects the corresponding x and y lines together. Polling is done by activating each x line in sequence and detecting which y lines then have a signal, when the keyboard processor detects that a key has changed state, it sends a signal to the CPU indicating the scan code of the key and its new state. The symbol is encoded, or converted into a number, based on the status of modifier keys. A custom encoding can be used for an application with no loss of data. However, using an encoding such as ASCII is problematic if a symbol such as ß needs to be converted but is not in the standard. It is estimated that in the year 1986 less than 1% of the technological capacity to store information was digital. The year 2002 is assumed to be the year when human kind was able to more information in digital than in analog format. In written or spoken human languages synchronization is typically provided by pauses, capitalization, machine communications typically use special synchronization sequences. Languages are generally arbitrary and specify the meaning to be assigned to particular symbol sequences, errors, Disturbances in analog communications invariably introduce some, generally small deviation or error between the intended and actual communication. Disturbances in a digital communication do not result in errors unless the disturbance is so large as to result in a symbol being misinterpreted as another symbol or disturb the sequence of symbols and it is therefore generally possible to have an entirely error-free digital communication
Digital works
6.
Digital Signal Processor
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A digital signal processor is a specialized microprocessor, with its architecture optimized for the operational needs of digital signal processing. The goal of DSPs is usually to measure, filter or compress continuous real-world analog signals, DSPs often use special memory architectures that are able to fetch multiple data or instructions at the same time. Digital signal processing algorithms typically require a number of mathematical operations to be performed quickly and repeatedly on a series of data samples. Signals are constantly converted from analog to digital, manipulated digitally, many DSP applications have constraints on latency, that is, for the system to work, the DSP operation must be completed within some fixed time, and deferred processing is not viable. A specialized digital signal processor, however, will tend to provide a lower-cost solution, with performance, lower latency. For example, the SES-12 and SES-14 satellites from operator SES, the architecture of a digital signal processor is optimized specifically for digital signal processing. Most also support some of the features as a processor or microcontroller. Some useful features for optimizing DSP algorithms are outlined below, sometimes various sticky bits operation modes are available. DSPs can sometimes rely on supporting code to know about cache hierarchies and this is a tradeoff that allows for better performance. In addition, extensive use of DMA is employed, DSPs frequently use multi-tasking operating systems, but have no support for virtual memory or memory protection. Operating systems that use virtual memory require more time for context switching among processes, the AMD2901 bit-slice chip with its family of components was a very popular choice. There were reference designs from AMD, but very often the specifics of a design were application specific. These bit slice architectures would sometimes include a peripheral multiplier chip, examples of these multipliers were a series from TRW including the TDC1008 and TDC1010, some of which included an accumulator, providing the requisite multiply–accumulate function. In 1976, Richard Wiggins proposed the Speak & Spell concept to Paul Breedlove, Larry Brantingham, two years later in 1978 they produced the first Speak & Spell, with the technological centerpiece being the TMS5100, the industrys first digital signal processor. It also set other milestones, being the first chip to use Linear predictive coding to perform speech synthesis, in 1978, Intel released the 2920 as an analog signal processor. It had an on-chip ADC/DAC with a signal processor. In 1979, AMI released the S2811 and it was designed as a microprocessor peripheral, and it had to be initialized by the host. The S2811 was likewise not successful in the market, in 1980 the first stand-alone, complete DSPs – the NEC µPD7720 and AT&T DSP1 – were presented at the International Solid-State Circuits Conference 80
Digital Signal Processor
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A digital signal processor chip found in a
guitar effects unit
7.
Conduction 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
Conduction current
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A simple electric circuit, where current is represented by the letter i. The relationship between the voltage (V), resistance (R), and current (I) is V=IR; this is known as
Ohm's Law.
8.
Electric magnet
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An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. The magnetic field disappears when the current is turned off, electromagnets usually consist of insulated wire wound into a coil. A current through the wire creates a field which is concentrated in the hole in the center of the coil. The main advantage of an electromagnet over a permanent magnet is that the field can be quickly changed by controlling the amount of electric current in the winding. However, unlike a permanent magnet that needs no power, an electromagnet requires a supply of current to maintain the magnetic field. Electromagnets are also employed in industry for picking up and moving heavy objects such as scrap iron. Danish scientist Hans Christian Ørsted discovered in 1820 that electric currents create magnetic fields, british scientist William Sturgeon invented the electromagnet in 1824. His first electromagnet was a piece of iron that was wrapped with about 18 turns of bare copper wire. The iron was varnished to insulate it from the windings, when a current was passed through the coil, the iron became magnetized and attracted other pieces of iron, when the current was stopped, it lost magnetization. Sturgeon displayed its power by showing that although it only weighed seven ounces, however, Sturgeons magnets were weak because the uninsulated wire he used could only be wrapped in a single spaced out layer around the core, limiting the number of turns. Beginning in 1830, US scientist Joseph Henry systematically improved and popularized the electromagnet, the first major use for electromagnets was in telegraph sounders. A portative electromagnet is one designed to just hold material in place, a tractive electromagnet applies a force and moves something. The solenoid is a coil of wire, and the plunger is made of a such as soft iron. Applying a current to the solenoid applies a force to the plunger, the plunger stops moving when the forces upon it are balanced. For example, the forces are balanced when the plunger is centered in the solenoid, the maximum uniform pull happens when one end of the plunger is at the middle of the solenoid. For units using inches, pounds force, and amperes with long, slender, solenoids, for example, a 12-inch long coil with a long plunger of 1-square inch cross section and 11,200 ampere-turns had a maximum pull of 8.75 pounds. The maximum pull is increased when a stop is inserted into the solenoid. The stop becomes a magnet that will attract the plunger, it adds little to the pull when the plunger is far away
Electric magnet
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Industrial electromagnet lifting scrap iron, 1914
Electric magnet
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A simple electromagnet consisting of a coil of insulated wire wrapped around an iron core. A core of ferromagnetic material like iron serves to increase the magnetic field created. The strength of magnetic field generated is proportional to the amount of current through the winding.
Electric magnet
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Laboratory electromagnet. Produces 2 T field with 20 A current.
Electric magnet
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Magnet in a
mass spectrometer
9.
Solenoid Valve
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A solenoid valve is an electromechanically operated valve. Multiple solenoid valves can be placed together on a manifold, solenoid valves are the most frequently used control elements in fluidics. Their tasks are to shut off, release, dose, distribute or mix fluids and they are found in many application areas. Solenoids offer fast and safe switching, high reliability, long life, good medium compatibility of the materials used, low control power. Besides the plunger-type actuator which is used most frequently, pivoted-armature actuators, there are many valve design variations. Ordinary valves can have ports and fluid paths. A 2-way valve, for example, has 2 ports, if the valve is open, then the two ports are connected and fluid may flow between the ports, if the valve is closed, then ports are isolated. If the valve is open when the solenoid is not energized, similarly, if the valve is closed when the solenoid is not energized, then the valve is termed normally closed. There are also 3-way and more complicated designs, a 3-way valve has 3 ports, it connects one port to either of the two other ports. Solenoid valves are also characterized by how they operate, a small solenoid can generate a limited force. If that force is sufficient to open and close the valve, a typical solenoid force might be 15 N. An application might be a low pressure gas with a small orifice diameter, when high pressures and large orifices are encountered, then high forces are required. To generate those forces, an internally piloted solenoid valve design may be possible, in such a design, the line pressure is used to generate the high valve forces, a small solenoid controls how the line pressure is used. Internally piloted valves are used in dishwashers and irrigation systems where the fluid is water, the pressure might be 80 pounds per square inch, in some solenoid valves the solenoid acts directly on the main valve. Others use a small, complete solenoid valve, known as a pilot, while the second type is actually a solenoid valve combined with a pneumatically actuated valve, they are sold and packaged as a single unit referred to as a solenoid valve. Piloted valves require much less power to control, but they are noticeably slower, a direct acting solenoid valve typically operates in 5 to 10 milliseconds. The operation time of a piloted valve depends on its size, power consumption and supply requirements of the solenoid vary with application, being primarily determined by fluid pressure and line diameter. For example, a popular 3/4150 psi sprinkler valve, intended for 24 VAC residential systems, has an inrush of 7.2 VA
Solenoid Valve
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Solenoid valves.
Solenoid Valve
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The solenoid valve (small black box at the top of the photo) with input air line (small green tube) used to actuate a larger
rack and pinion actuator (gray box) which controls the water pipe valve.
Solenoid Valve
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Example core tubes. Non-magnetic core tubes are used to isolate the fluid from the coil. The core tube encloses the plugnut, the core spring, and the core. The coil slips over the core tube; a retaining clip engages the depression near the closed end of the core tube and holds the coil on the core tube.
