Hall Effect Sensor - Report Example

Report on a Smart Device: Hall Effect Sensor Background/why it was developed An example of a smart device is a. This device is basically a transducerwhose voltage output varies in response to a magnetic field. The need for the development of the Hall Effect sensor finds its roots in the need to upgrade the technological discovery made in 1879 by an American scientist called Edwin Hall. According to WELLS Counter Point (1999), Hall discovered a new electrical phenomenon in 1879. In this situation, Hall applied electric current to a metal that was put or inserted between two magnets and he observed that it generated a secondary voltage in the metal. This voltage was at right angle to the voltage that was applied. The discovery of Hall did not have much use at the time but it turned out to be what future engineers would require to come up with a switching device that is able to produce an efficient signal and this is an on-off square-wave voltage. The Hall Effect was therefore adapted to ensure that the change in voltage would occur in silicone chip that was put at a right angle to an existing magnetic field. The successful utilization of the Hall Effect necessitated the need to have Hall Effect sensors to detect surfaces experiencing the Hall Effect. Detail structure and geometry In terms of structure, a Hall Effect sensor basically consists of thin piece of a semiconductor material that is of rectangular p-type and that passes a continuous current via itself (Ramsden, 2006). This is illustrated in figure 1s below. The materials that can be used as rectangular p-type semiconductors could be indium antimonide (InSb), gallium arsenide (GaAs) or indium arsenide (InAs). Popovic (2004) explains that the sensor is integrated with a permanent magnet or a wound core that surrounds the conductor to be measured. A typical hall effect sensor has three terminals or wires. Of these wires, one is for reference voltage or supply, one is for ground and the other is for the output signal. Design principle/how it works A Hall Effect sensor is activated by the surrounding magnetic field. Gardner etal (2001) state that in its simplest form, a Hall Effect sensor works as an analogue transducer, returning a voltage directly. When the sensor is placed in a magnetic field, a force is exerted on the semi-conductor material by the present magnetic flux lines. This force deflects the electrons, holes and charge carriers to left or the right side of the semiconductor slab (Fraden, 1997). The movement of charge carriers that occurs is a result of the magnetic force these carriers experience as they move through the semiconductor material. Hauptman (1991) points out that as these holes and electrons move side wards, a build-up of these charge carriers produces a potential difference between the two sides of the semiconductor material. As a result of the above, the movement of electrons through the semiconductor is affected by the availability of an external magnetic field which is normally at right angles to it. The effect of this magnetic field is much felt in a flat rectangular material. Hall effect sensors are available either with digital output or linear output. Those which operate with linear output are called analogue sensors. The output signal for analogue or linear sensors is retrieved directly from the operational amplifier’s output. The voltage output in this case is directly proportional to the magnetic field moving through the Hall Effect sensor. The output voltage is given as VH=RH[I/t X B]. Where VH is the Hall Voltage (given in volts). RH is the co-efficient of the Hall Effect I is the amount of current flowing through the sensor (given in amps) t is the thickness of the sensor (given in mm) B is the Magnetic Flux density (given in Teslas) (Electronics-Tutorials.ws., 2011). Moseley and Crocker (1996) explain that the analogue or linear Hall Effect sensors continuously give a voltage output that rises with a strong magnetic field and decreases whenever there is a weak magnetic field. One phenomena that is notable in this type of sensor is that when there is an increase in the strength of the magnetic field, there is also a rise in the output signal from the amplifier until it begins to saturate the by the limits that the power supply has imposed on it. Any additional magnetic field will not have any effect on the output. Instead, it just drives it into saturation. On the other hand, the digital output Hall Effect sensors have a Schmitt-trigger with an internally built hysteresis that is connected to the op-amp. The design principle in this type of senor is that when the magnetic flux moving via the Hall sensor surpasses the value that is already preset, the output from the device quickly switches from its “ON” condition from an “OFF” condition without any form of contact bounce. Operations conditions Weiser (1991) explains that for a Hall Effect sensor to produce an output signal, a reference voltage must be supplied to it. This voltage is supplied from the vehicle’s onboard computer. This could be which may be 5 to 12 volts depending on the application. This supply of voltage is required for the creation of the switching effect that occurs inside the sensor. The main applications of Hall Effect sensors are proximity switching, speed detection, positioning and current sensing applications. Pros and cons One main advantage of an hall effect sensor is that when packaged appropriately, it is immune to water, mud and dust. These characteristics make hall effect sensors a better option for position sensing than alternative options for example electromechanical and optical sensing. The electricity conducted via a conductor yields a magnetic field that varies with the existing current. Because of this, a Hall Effect sensor can be used to measure the amount of current without interrupting the electric circuit in any way (Electronics-Tutorials.ws., 2011). The inbuilt hysterics found in the digital output type of Hall Effect sensors eliminate any oscillation of the resultant output signal as the Hall Effect sensor into and out of the magnetic field. As a result of their design, the non-linear sensors can be made to trigger the output “ON” at a air gap distance that has already been preset away from the magnet and this is used for indicating positional detection. Popovic (1991) states that the linear Hall Effect sensors are in position to distinguish between negative and positive magnetic fields. According to WELLS Counter Point (1999), Hall Effect sensors differs from magnetic sensors that yield alternating current signals which produces different voltages under different speeds. On their part, Hall Effect sensors yield constant voltage signal that is capable of changing abruptly from maximum voltage to almost zero and back to again despite the speed of the engine. The signal resulting from this action results is a square wave output and this can easily be utilised by the onboard computer for purposes of timing. Moseley and Crocker (1996) reveals like other hall effect devices, the signal levels of hall effect sensors are very low and therefore they require amplification. In relation to this, they cannot switch large loads directly. This is because their output drive capabilities are very low, ranging from 10 to 20mA. Problems and issues The Hall Effect sensor must be supplied with the proper amounts of reference voltage power from the computer. If the sensor is not receiving the correct supply of voltage, it will not work. References Electronics-Tutorials.ws. (2011). Hall Effect Sensor. Online: http://www.electronics-tutorials.ws/electromagnetism/hall-effect.html. Viewed on 1st September, 2011. Fraden, J. (1997). Handbook for modern sensors. Springer. New York. Gardner, J. Varadan, V. and Awadelkarim, O. Microsensors (2001). MEMS, and smart devices. John Wiley and Sons. New York. Hauptman, P. (1991). Sensors: principles and applications. Prentice Hall. New York. Moseley, P. and Crocker, A. (1996). Sensor materials. Bristol. IOP publishing. Ramsden, E. (2006). Hall-effect sensors: theory and applications (2, ilustrated ed.). Elsevier. Popovic, R. (1991). Hall Effect devices: Magnetic sensors and Characterization of Semiconductors. Bristol. IOP Publishing. Popovic, R. (2004). Hall Effect devices. (illustrated ed). CRC Press. Weiser, M. (1991). “The Computer for the Twenty-First Century”. Scientific American (3) pp 94–104. WELLS Counter Point. (1999). Understanding Hall Effect Sensors. WELLS Counter Point. (1) pp 1-4. Appendix Figure. 1 Hall Effect Sensor Figure. 2 Hall Effect Sensors Read More