Variable reluctance sensor
A variable reluctance sensor is a transducer that measures changes in magnetic reluctance. When combined with basic electronic circuitry, the sensor detects the change in presence or proximity of ferrous objects. With more complex circuitry and the addition of software and specific mechanical hardware, a VR sensor can provide measurements of linear velocity, angular velocity and torque. A VR sensor used as a simple proximity sensor can determine the position of a mechanical link in a piece of industrial equipment. A Crankshaft position sensor is used to provide the angular position of the crankshaft to the Engine control unit; the Engine control unit can calculate engine speed. Speed sensors used in automobile transmissions, are used to measure the rotational speed of shafts within the transmission; the Engine control unit or Transmission control unit uses these sensors to determine when to shift from one gear to the next. A pickup used in an electric guitar detect vibrations of the metallic "strings".
See Pickup for details of this application. This sensor consists of a permanent magnet, a ferromagnetic pole piece, coil of wire. VR sensor interface circuits VR sensors need waveform shaping for their output to be digitally readable; the normal output of a VR sensor is an analog signal, shaped much like a sine wave. The frequency and amplitude of the analog signal is proportional to the target's velocity; this waveform needs to be squared up, flattened off by a comparator like electronic chip to be digitally readable. While discrete VR sensor interface circuits can be implemented, the semiconductor industry offers integrated solutions. Examples are the MAX9924 to MAX9927 VR sensor interface IC from Maxim Integrated products, LM1815 VR sensor amplifier from National Semiconductor and NCV1124 from ON semiconductor. An integrated VR sensor interface circuit like the MAX9924 features a differential input stage to provide enhanced noise immunity, Precision Amplifier and Comparator with user enabled Internal Adaptive Peak Threshold or user programmed external threshold to provide a wide dynamic range and zero-crossing detection circuit to provide accurate phase Information.
To measure angular position or rotational speed of a shaft, a toothed ring made of ferrous material can be attached to the shaft. As the teeth of the rotating wheel pass by the face of the magnet, the amount of magnetic flux passing through the magnet and the coil varies; when the gear tooth is close to the sensor, the flux is at a maximum. When the tooth is further away, the flux drops off; the moving target results in a time-varying flux. Subsequent electronics are used to process this signal to get a waveform that can be more counted and timed; this system has been employed in ABS braking. By attaching two reluctor rings to a shaft, the torque can be measured; the tooth spacing on reluctor rings may be uneven. Although VR sensors are based on mature technology, they still offer several significant advantages; the first is low cost - coils of wire and magnets are inexpensive. The low cost of the transducer is offset by the cost of the additional signal-processing circuitry needed to recover a useful signal.
And because the magnitude of the signal developed by the VR sensor is proportional to target speed, it is difficult to design circuitry to accommodate very-low-speed signals. A given VR-sensing system has a definite limit as to how slow the target can move and still develop a usable signal. An alternative but more expensive technology is Hall effect sensor. Hall effect sensors are true zero-rpm sensors and supply information when there's no transmission motion at all. One area in which VR sensors excel, however, is in high-temperature applications; because operating temperature is limited by the characteristics of the materials used in the device, with appropriate construction VR sensors can be made to operate at temperatures in excess of 300 °C. An example of such an extreme application is sensing the turbine speed of a jet engine or engine cam shaft and crankshaft position control in an automobile
Omniview technology is a vehicle parking assistant technology that first became available in vehicle electronic products in 2007. It is designed to help drivers in parking a vehicle in small space. Early vehicle parking assistant products use proximity sensors or a single rear-view camera to get information about obstacles around, provide drivers with sound alarm or rear-view video. There are some drawbacks about such products: the alarm is not intuitive, the rear-view camera has blind area. However, omniview technology has seen increasing applications. In a common omniview system, there are four wide-field cameras: one in the front of the vehicle, one in the back of the vehicle, one in the left rear view mirror, one in the right outside mirror; the four cameras cover the whole area around vehicle. The system synthesizes a bird view image in front of the vehicle by distortion correction, projection transformation, image fusion; the images shown below are output of a common omniview product. Omniview suppliers Mobileye Israel Fujitsu Japan Percherry China
A transformer is a static electrical device that transfers electrical energy between two or more circuits. A varying current in one coil of the transformer produces a varying magnetic flux, which, in turn, induces a varying electromotive force across a second coil wound around the same core. Electrical energy can be transferred between the two coils, without a metallic connection between the two circuits. Faraday's law of induction discovered in 1831 described the induced voltage effect in any coil due to changing magnetic flux encircled by the coil. Transformers are used for increasing or decreasing the alternating voltages in electric power applications, for coupling the stages of signal processing circuits. Since the invention of the first constant-potential transformer in 1885, transformers have become essential for the transmission and utilization of alternating current electric power. A wide range of transformer designs is encountered in electric power applications. Transformers range in size from RF transformers less than a cubic centimeter in volume, to units weighing hundreds of tons used to interconnect the power grid.
An ideal transformer is a theoretical linear transformer, lossless and coupled. Perfect coupling implies infinitely high core magnetic permeability and winding inductances and zero net magnetomotive force. A varying current in the transformer's primary winding attempts to create a varying magnetic flux in the transformer core, encircled by the secondary winding; this varying flux at the secondary winding induces a varying electromotive force in the secondary winding due to electromagnetic induction and the secondary current so produced creates a flux equal and opposite to that produced by the primary winding, in accordance with Lenz's law. The windings are wound around a core of infinitely high magnetic permeability so that all of the magnetic flux passes through both the primary and secondary windings. With a voltage source connected to the primary winding and load impedance connected to the secondary winding, the transformer currents flow in the indicated directions and the core magnetomotive force cancels to zero.
According to Faraday's law, since the same magnetic flux passes through both the primary and secondary windings in an ideal transformer, a voltage is induced in each winding proportional to its number of windings. Thus, referring to the equations shown in the sidebox at right, according to Faraday's law, we have primary and secondary winding voltages defined by eq. 1 & eq. 2, respectively. The primary EMF is sometimes termed counter EMF; this is in accordance with Lenz's law, which states that induction of EMF always opposes development of any such change in magnetic field. The transformer winding voltage ratio is thus shown to be directly proportional to the winding turns ratio according to eq. 3. However, some sources use the inverse definition. According to the law of conservation of energy, any load impedance connected to the ideal transformer's secondary winding results in conservation of apparent and reactive power consistent with eq. 4. The ideal transformer identity shown in eq. 5 is a reasonable approximation for the typical commercial transformer, with voltage ratio and winding turns ratio both being inversely proportional to the corresponding current ratio.
By Ohm's law and the ideal transformer identity: the secondary circuit load impedance can be expressed as eq. 6 the apparent load impedance referred to the primary circuit is derived in eq. 7 to be equal to the turns ratio squared times the secondary circuit load impedance. The ideal transformer model neglects the following basic linear aspects of real transformers: Core losses, collectively called magnetizing current losses, consisting of Hysteresis losses due to nonlinear magnetic effects in the transformer core, Eddy current losses due to joule heating in the core that are proportional to the square of the transformer's applied voltage. Unlike the ideal model, the windings in a real transformer have non-zero resistances and inductances associated with: Joule losses due to resistance in the primary and secondary windings Leakage flux that escapes from the core and passes through one winding only resulting in primary and secondary reactive impedance. Similar to an inductor, parasitic capacitance and self-resonance phenomenon due to the electric field distribution.
Three kinds of parasitic capacitance are considered and the closed-loop equations are provided Capacitance between adjacent turns in any one layer. However, the capacitance effect can be measured by comparing open-circuit inductance, i.e. the inductance of a primary winding when the secondary circuit is open, to a short-circuit inductance when the secondary winding is shorted. The ideal transformer model assumes that all flux generated by the primary winding links all the turns of every winding, including itself. In practice, some flux traverses paths; such flux is termed leakage flux, results in leakage inductance in series with the mutually coupled transformer windings. Leakage flux results in energy being alternately stored in and discharged from the magnetic fields with each cycle of the power supply, it is not directly a power loss, but results in inferior voltage regulation, causing the secondary voltage not to be directly proportional to the primary voltage under heavy load. Transformers are therefore designed to have low
A seismometer is an instrument that responds to ground motions, such as caused by earthquakes, volcanic eruptions, explosions. Seismometers are combined with a timing device and a recording device to form a seismograph; the output of such a device — recorded on paper or film, now recorded and processed digitally — is a seismogram. Such data is used to locate and characterize earthquakes, to study the earth's internal structure. A simple seismometer, sensitive to up-down motions of the Earth, is like a weight hanging from a spring, both suspended from a frame that moves along with any motion detected; the relative motion between the weight and the frame provides a measurement of the vertical ground motion. A rotating drum is attached to the frame and a pen is attached to the weight, thus recording any ground motion in a seismogram. Any movement of the ground moves the frame; the mass tends not to move because of its inertia, by measuring the movement between the frame and the mass, the motion of the ground can be determined.
Early seismometers used optical levers or mechanical linkages to amplify the small motions involved, recording on soot-covered paper or photographic paper. Modern instruments use electronics. In some systems, the mass is held nearly motionless relative to the frame by an electronic negative feedback loop; the motion of the mass relative to the frame is measured, the feedback loop applies a magnetic or electrostatic force to keep the mass nearly motionless. The voltage needed to produce this force is the output of the seismometer, recorded digitally. In other systems the weight is allowed to move, its motion produces an electrical charge in a coil attached to the mass which voltage moves through the magnetic field of a magnet attached to the frame; this design is used in a geophone, used in exploration for oil and gas. Seismic observatories have instruments measuring three axes: north-south, east-west, vertical. If only one axis is measured, it is the vertical because it is less noisy and gives better records of some seismic waves.
The foundation of a seismic station is critical. A professional station is sometimes mounted on bedrock; the best mountings may be in deep boreholes, which avoid thermal effects, ground noise and tilting from weather and tides. Other instruments are mounted in insulated enclosures on small buried piers of unreinforced concrete. Reinforcing rods and aggregates would distort the pier as the temperature changes. A site is always surveyed for ground noise with a temporary installation before pouring the pier and laying conduit. European seismographs were placed in a particular area after a destructive earthquake. Today, they are concentrated in high-risk regions; the word derives from the Greek σεισμός, seismós, a shaking or quake, from the verb σείω, seíō, to shake. Seismograph is another Greek term from γράφω, gráphō, to draw, it is used to mean seismometer, though it is more applicable to the older instruments in which the measuring and recording of ground motion were combined, than to modern systems, in which these functions are separated.
Both types provide a continuous record of ground motion. The technical discipline concerning such devices is called seismometry, a branch of seismology; the concept of measuring the "shaking" of something means that the word "seismograph" might be used in a more general sense. For example, a monitoring station that tracks changes in electromagnetic noise affecting amateur radio waves presents an rf seismograph, and Helioseismology studies the "quakes" on the Sun. The first seismometer was made in China during the 2nd Century; the first Western description of the device comes from the French physicist and priest Jean de Hautefeuille in 1703. The modern seismometer was developed in the 19th century. In December 2018, a seismometer was deployed on the planet Mars by the InSight lander, the first time a seismometer was placed onto the surface of another planet. In AD 132, Zhang Heng of China's Han dynasty invented the first seismoscope, called Houfeng Didong Yi; the description we have, from the History of the Later Han Dynasty, says that it was a large bronze vessel, about 2 meters in diameter.
When there was an earthquake, one of the dragons' mouths would open and drop its ball into a bronze toad at the base, making a sound and showing the direction of the earthquake. On at least one occasion at the time of a large earthquake in Gansu in AD 143, the seismoscope indicated an earthquake though one was not felt; the available text says that inside the vessel was a central column that could move along eight tracks. The first earthquake recorded by this seismoscope was "somewhere in the east". Days a rider from the east reported this earthquake. By the 13th century, seismographic devices existed in the Maragheh observatory in Persia. French physicist and priest Jean de Hautefeuille built one in 1703. After 1880, most seismometers were descend
Mass flow sensor
A mass flow sensor is a sensor used to determine the mass flow rate of air entering a fuel-injected internal combustion engine. The air mass information is necessary for the engine control unit to balance and deliver the correct fuel mass to the engine. Air changes its density with pressure. In automotive applications, air density varies with the ambient temperature and the use of forced induction, which means that mass flow sensors are more appropriate than volumetric flow sensors for determining the quantity of intake air in each cylinder. There are two common types of mass airflow sensors in use on automotive engines; these are the hot wire. Neither design employs technology. However, with additional sensors and inputs, an engine's ECU can determine the mass flow rate of intake air. Both approaches are used exclusively on electronic fuel injection engines. Both sensor designs output a 0.0–5.0 volt or a pulse-width modulation signal, proportional to the air mass flow rate, both sensors have an intake air temperature sensor incorporated into their housings for most post on-board diagnostics vehicles.
Vehicles prior to 1996 could have MAF without an IAT. An example is 1994 Infiniti Q45; when a MAF sensor is used in conjunction with an oxygen sensor, the engine's air/fuel ratio can be controlled accurately. The MAF sensor provides the open-loop controller predicted air flow information to the ECU, the oxygen sensor provides closed-loop feedback in order to make minor corrections to the predicted air mass. See manifold absolute pressure sensor; the VAF sensor measures the air flow into the engine with a spring-loaded air vane attached to a variable resistor. The vane moves in proportion to the airflow. A voltage is applied to the potentiometer and a proportional voltage appears on the output terminal of the potentiometer in proportion to the angle the vane rotates, or the movement of the vane may directly regulate the amount of fuel injected, as in the K-Jetronic system. Many VAF sensors have an air-fuel adjustment screw, which opens or closes a small air passage on the side of the VAF sensor.
This screw controls the air-fuel mixture by letting a metered amount of air flow past the air flap, thereby leaning or richening the mixture. By turning the screw clockwise the mixture is counterclockwise the mixture is leaned; the vane moves because of the drag force of the air flow against it. The drag force depends on air velocity and the shape of the vane, see drag equation; some VAF sensors include an additional intake air temperature sensor to allow the engines ECU to calculate the density of the air, the fuel delivery accordingly. The vane meter approach has some drawbacks: it restricts airflow which limits engine output its moving electrical or mechanical contacts can wear finding a suitable mounting location within a confined engine compartment is problematic the vane has to be oriented with respect to gravity. In some manufacturers fuel pump control was part on the VAF internal wiring. A hot wire mass airflow sensor determines the mass of air flowing into the engine’s air intake system.
The theory of operation of the hot wire mass airflow sensor is similar to that of the hot wire anemometer. This is achieved by heating a wire suspended in the engine’s air stream, like a toaster wire, with either a constant voltage over the wire or a constant current through the wire; the wire's electrical resistance increases as the wire’s temperature increases, which varies the electrical current flowing through the circuit, according to Ohm's law. When air flows past the wire, the wire cools, decreasing its resistance, which in turn allows more current to flow through the circuit, since the supply voltage is a constant; as more current flows, the wire’s temperature increases until the resistance reaches equilibrium again. The current increase or decrease is proportional to the mass of air flowing past the wire; the integrated electronic circuit converts the proportional measurement into a calibrated signal, sent to the ECU. If air density increases due to pressure increase or temperature drop, but the air volume remains constant, the denser air will remove more heat from the wire indicating a higher mass airflow.
Unlike the vane meter's paddle sensing element, the hot wire responds directly to air density. This sensor's capabilities are well suited to support the gasoline combustion process which fundamentally responds to air mass, not air volume; this sensor sometimes employs a mixture screw, but this screw is electronic and uses a variable resistor instead of an air bypass screw. The screw needs more turns to achieve the desired results. A hot wire burn-off cleaning circuit is employed on some of these sensors. A burn-off relay applies a high current through the platinum hot wire after the vehicle is turned off for a second or so, thereby burning or vaporizing any contaminants that have stuck to the platinum hot wire element; the hot film MAF sensor works somewhat similar to the hot wire MAF sensor, but instead it outputs a frequency signal. This sensor uses a hot film-grid instead of a hot wire, it is found in late 80’s early 90’s fuel-injected vehicles. The output frequency is directly proportional to the air mass entering the engine.
So as mass flow increases so does frequency. These sensors tend to cause intermittent problems due to internal electrical failures; the use of an oscilloscope is recommended to check the outp
A radar speed gun is a device used to measure the speed of moving objects. It is used in law-enforcement to measure the speed of moving vehicles and is used in professional spectator sport, for things such as the measurement of bowling speeds in cricket, speed of pitched baseballs and tennis serves. A radar speed gun is a Doppler radar unit that may be vehicle-mounted or static, it measures the speed of the objects at which it is pointed by detecting a change in frequency of the returned radar signal caused by the Doppler effect, whereby the frequency of the returned signal is increased in proportion to the object's speed of approach if the object is approaching, lowered if the object is receding. Such devices are used for speed limit enforcement, although more modern LIDAR speed gun instruments, which use pulsed laser light instead of radar, began to replace radar guns during the first decade of the twenty-first century, because of limitations associated with small radar systems; the radar speed gun was invented by John L. Barker Sr. and Ben Midlock, who developed radar for the military while working for the Automatic Signal Company in Norwalk, CT during World War II.
Automatic Signal was approached by Grumman Aircraft Corporation to solve the specific problem of terrestrial landing gear damage on the now-legendary PBY Catalina amphibious aircraft. Barker and Midlock cobbled a Doppler radar unit from coffee cans soldered shut to make microwave resonators; the unit was installed at the end of the runway, aimed directly upward to measure the sink rate of landing PBYs. After the war and Midlock tested radar on the Merritt Parkway. In 1947, the system was tested by the Connecticut State Police in Glastonbury, Connecticut for traffic surveys and issuing warnings to drivers for excessive speed. Starting in February 1949, the state police began to issue speeding tickets based on the speed recorded by the radar device. In 1948, radar was used in Garden City, New York. Speed guns use Doppler radar to perform speed measurements. Radar speed guns, like other types of radar, consist of receiver, they send out a radio signal in a narrow beam receive the same signal back after it bounces off the target object.
Due to a phenomenon called the Doppler effect, if the object is moving toward or away from the gun, the frequency of the reflected radio waves when they come back is different from the transmitted waves. When the object is approaching the radar, the frequency of the return waves is higher than the transmitted waves. From that difference, the radar speed gun can calculate the speed of the object from which the waves have been bounced; this speed is given by the following equation: v = Δ f f c 2 where c is the speed of light, f is the emitted frequency of the radio waves and Δf is the difference in frequency between the radio waves that are emitted and those received back by the gun. This equation holds only when object speeds are low compared to that of light, but in everyday situations, this is the case and the velocity of an object is directly proportional to this difference in frequency. After the returning waves are received, a signal with a frequency equal to this difference is created by mixing the received radio signal with a little of the transmitted signal.
Just as two different musical notes played together create a beat note at the difference in frequency between them, so when these two radio signals are mixed they create a "beat" signal. An electrical circuit measures this frequency using a digital counter to count the number of cycles in a fixed time period, displays the number on a digital display as the object's speed. Since this type of speed gun measures the difference in speed between a target and the gun itself, the gun must be stationary in order to give a correct reading. If a measurement is made from a moving car, it will give the difference in speed between the two vehicles, not the speed of the target relative to the road, so a different system has been designed to work from moving vehicles. In so-called "moving radar", the radar antenna receives reflected signals from both the target vehicle and stationary background objects such as the road surface, nearby road signs, guard rails and streetlight poles. Instead of comparing the frequency of the signal reflected from the target with the transmitted signal, it compares the target signal with this background signal.
The frequency difference between these two signals gives the true speed of the target vehicle. Modern radar speed guns operate at X, K, Ka, Ku bands. Radar guns that operate using the X band frequency range are becoming less common because they produce a strong and detectable beam. Most automatic doors utilize radio waves in the X band range and can affect the readings of police radar; as a result, K band and Ka band are most used by police agencies. Some motorists install radar detectors which can alert them to the presence of a speed trap ahead, the microwave signals from radar may change the quality of reception of AM and FM radio signals when tuned to a weak station. For these reasons, hand-held radar includes an on-off trigger and the radar is only turned on when the operator is about to make a measurement. Radar detectors are illegal in some areas. Traffic radar comes in many models. Hand-held units are b
A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, terminate transmission lines, among other uses. High-power resistors that can dissipate many watts of electrical power as heat, may be used as part of motor controls, in power distribution systems, or as test loads for generators. Fixed resistors have resistances that only change with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements, or as sensing devices for heat, humidity, force, or chemical activity. Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment. Practical resistors as discrete components can be composed of various forms. Resistors are implemented within integrated circuits; the electrical function of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than nine orders of magnitude.
The nominal value of the resistance falls within the manufacturing tolerance, indicated on the component. Two typical schematic diagram symbols are as follows: The notation to state a resistor's value in a circuit diagram varies. One common scheme is the RKM code following IEC 60062, it avoids using a decimal separator and replaces the decimal separator with a letter loosely associated with SI prefixes corresponding with the part's resistance. For example, 8K2 as part marking code, in a circuit diagram or in a bill of materials indicates a resistor value of 8.2 kΩ. Additional zeros imply a tighter tolerance, for example 15M0 for three significant digits; when the value can be expressed without the need for a prefix, an "R" is used instead of the decimal separator. For example, 1R2 indicates 1.2 Ω, 18R indicates 18 Ω. The behaviour of an ideal resistor is dictated by the relationship specified by Ohm's law: V = I ⋅ R. Ohm's law states that the voltage across a resistor is proportional to the current, where the constant of proportionality is the resistance.
For example, if a 300 ohm resistor is attached across the terminals of a 12 volt battery a current of 12 / 300 = 0.04 amperes flows through that resistor. Practical resistors have some inductance and capacitance which affect the relation between voltage and current in alternating current circuits; the ohm is the SI unit of electrical resistance, named after Georg Simon Ohm. An ohm is equivalent to a volt per ampere. Since resistors are specified and manufactured over a large range of values, the derived units of milliohm and megohm are in common usage; the total resistance of resistors connected in series is the sum of their individual resistance values. R e q = R 1 + R 2 + ⋯ + R n; the total resistance of resistors connected in parallel is the reciprocal of the sum of the reciprocals of the individual resistors. 1 R e q = 1 R 1 + 1 R 2 + ⋯ + 1 R n. For example, a 10 ohm resistor connected in parallel with a 5 ohm resistor and a 15 ohm resistor produces 1/1/10 + 1/5 + 1/15 ohms of resistance, or 30/11 = 2.727 ohms.
A resistor network, a combination of parallel and series connections can be broken up into smaller parts that are either one or the other. Some complex networks of resistors cannot be resolved in this manner, requiring more sophisticated circuit analysis; the Y-Δ transform, or matrix methods can be used to solve such problems. At any instant, the power P consumed by a resistor of resistance R is calculated as: P = I 2 R = I V = V 2 R where V is the voltage across the resistor and I is the current flowing through it. Using Ohm's law, the two other forms can be derived; this power is converted into heat which must be dissipated by the resistor's package before its temperature rises excessively. Resistors are rated according to their maximum power dissipation. Discrete resistors in solid-state electronic systems are rated as 1/10, 1/8, or 1/4 watt, they absorb much less than a watt of electrical power and require little attention to their power rating. Resistors required to dissipate substantial amounts of power used in power supplies, power conversion circuits, power amplifiers, are referred to as power resistors.
Power resistors are physically larger and may not use the preferred values, color codes, external packages described below. If the average power dissipated by a resistor is more than its power rating, damage to the resistor may occur, permanently altering its resistance. Excessive power dissip