| Hall sensor, which is based on Hall effects, could convert magnetic signal into voltage. With simple structure, small volume, no touches, high stability and easy micromation, this probe can detect invariable and variable magnetic signal, and is widely used in industry, electrommunication, national defense and other fields. But different Hall probe has different integral sensitivity in the same working current, and when the magnetic signal is high, the voltage of Hall probe becomes nonlinear, so Hall probe must be re-calibrated when it is replaced from the equipment. Since Hall probe has such defects, this paper makes microprocessor of AT89C52 control power of magnetic to modulate working current and boost up intensity of magnetic field to 2.5T steadily. When the value of magnetic is lower than 1.0T, the output of Hall probe takes on good linearity with the result of fluxmeter. Therefore we can modulate working current of Hall probe through controlling D/A converter, and make the voltage of Hall equal to H0, the output of fluxmeter, then complete the Calibration in linear area. When the intensity of magnetic field is higher than 1.2T, the output of Hall probe becomes nonlinear, and the results of A/D conversion must be corrected before achieving the exact magnitude of magnetic field. In this article, different intensity of magnetic field are tested by fluxmeter, and the datas can be arranged in increasing order into two forms, one is the precise data of magnetic signal, and the other is the data of Hall probe, both of which are saved in E2PROM. 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 could be acquired by linear drawing up. This paper introduces the self-calibration system of Hall probe 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. Voltage of invariable current source, which provides working current of Hall probe by amplifier LM358, is controlled by D/A converter MAX5812. Compensation of inequipotential circuit includes compensatory net of bridge model,which could accomplish compensation both in breadth and... |
