Development Of Hall Sensor Characteristic Curve Measuring Lnstrument

Hall sensor is one of the most extensive magnetism sensor. It not only can be used to measure the magnetism but also can measure the physics such as current, velocity, position, angle and so on. And Hall sensor is also used in the filed of exactitude measurement, industry automatism control, automobile and implements.This paper is mainly about the problem of Hall characteristic parameter measurement. This system uses the AT89C52 as the CPU of theinstrument, the MAX110 as the core of data acquisition circuit. And send out the data through theserial communication controller to PC, so the magnetostrictiveparameters can be measured by automatic. This paper makes microprocessor of AT89C52 control power of magnetic to modulate working current and boost up intensity of magnetic field steadily. Therefore we can modulate working current of Hall probe through controlling D/A converter, and make the voltage of Hall equal to H0. When working practically, it should compare the output of Hall probe with the data in the second form to find out the area that the output located in. Real magnitude of magnetic signal. This paper introduces the self-calibration system of Hall characteristic parameter by means of hardware and software structure. Hardware system includes Hall probe, fluxmeter, circuit of photoelectricity isolation, memory, display, interface of keyboard and communication with PC. The device of Hall probe includes probe, D/A converter, invariable current source controlled by voltage, compensation of inequipotential circuit, signal magnifying, auto-switch of measurement, and A/D converter.The apparatus use Lm336 as constant voltage source, and it been converted to constant current source by amplification, which provide current for the Hall probe. The nonidiostatic offset circuit use the bridge method to offset the circuit.So while the magnetic density is null, the output voltage of Hall probeis null too.Signal magnifying is achieved by three operation amplifiers OP07, which has a very high input impedance, and could manage the faint signal of probe efficiently. The magneticflux meter circuit is composed by measuring coil and integrator. The measuring coil is made by the enamel wires which are wind to sample and the wires'diametric is less than 0.4 mm.The integrator includes the chopperstabilized Amplifier ICL7650, and it has high precision because of using exact input resistance and integral capacitance. The extension measurement signal is passing by the electric displacement sensor and amplified by OP07, then the signal is put into the A/D converter, and it can be calibrated by software and hardware. The core of data acquisition circuit is MAX110, which has two channel and 14bit A/D converter. Because the Hall probe circuit, magneticflux meter circuit and extension measurement circuit share the same A/D converter, but MAX110 only have two channel, so the system use CD4052. CD4052 is the analog switch controlled by microcomputer, which can switch the three input channels. The singles is passed to microcomputer after A/D converted.All artificial circuit and microcomputer is isolated with photocoupler. The lowfrequency control lines use TPL521, the high ones use 6N137. Isolation circuit restrains the keenedged impulse and other kinds of noise, and increases the radio of signal. In order to measure automatic, system use X24C45 to store the parameters.The X24C45 is a serial 256 bit NOVRAM featuring a static Ram configured 16×16, overlaid Bitbybit with a nonvolatile EEPROM array. It can automatically perform a store operation when Vcc falls below a preset threshold. The instrument read the parameters when the power is turn on by program, so the instrument can return to the state which used last time. The display and keyboard circuit used the IC 8279. The 8279 is a programmable keyboard and display interface designed for use with microprocessors. The instrument use 8279 to expansion seven key and three display group with fourhalf meter, which can sequential show the data of magneticflux, extension capacity, magnetic density. Low cost MAX232 is used in the serial communication controller circuit, function of which is to convert voltage from TTL to RS232 and communicate with PC.The host machine's software is program by assembly language, which can automatic control the host. The procedure includes the main program segment, the initialization program segment, the A/D convert program segment, X24C45 program e segment, the key interrupt program segment, the serial port interrupt program segment, data communication program segment, the display program segment and dataprocessing program segment.The instrument'PC software is program by VB 6.0 and Measurement Studio. VB has the friendly interface and easy method for program, Measurement Studio provided a great deal of controls for use. The controls not only reduce the tedious of program, but also provide the method to build the virtual apparatus interface. So the user oriented system can be build.By the experimental verification, this system operates well. It has high accuracy to the magnetostrictive contents measuring of sam.