1. System structure

The hardware structure of the displacement measurement system of magnetoelastic displacement sensor is shown in Figure 4. Because the magnetoelastic displacement sensor adopts the form of 4~20 ma current loop output that conforms to the industrial control specification, it is necessary to first convert the output current signal of the sensor into voltage signal, then collect it for a/d conversion, and then output it to the single chip microcomputer for signal processing and communication processing, and finally transmit the desired sensor signal to the LCD and PC in binary mode. The circuit of the sensor is composed of sensor head, receiving circuit, signal shaping circuit, parameter calibration input circuit, computer processing circuit, display circuit, measurement parameter output circuit, etc.

2. Microprocessor circuit

The single chip microcomputer adopts ATMEL's 8-bit microprocessor AT89C4051 based on CMOS technology, which is compatible with all the instructions of MCS-51 product series. The chip contains 4KB flash EPROM. Its outstanding feature is that the chip is small in size, with only 20 pins, which is especially suitable for the planning of miniaturized systems. In addition, AT89C4051 is cheap and cost-effective.

3. Signal shaping circuit

The sliding digital filtering algorithm based on extracting the characteristic quantity of the measured signal is selected. As shown in the figure below, it is the analog signal waveform output by the magnetoelastic displacement sensor when the magnetic ring is in the suspended state. It can be seen that there is a disturbing signal with high frequency superimposed on the measured stability value, with a peak value of about 25mV and a period of 440 μ s。 If a single measurement value is directly sampled and transmitted to the controller, in the case of high-precision measurement, the probability of randomly obtaining abnormal measurement values is relatively high, and the error is 12 LSBs. Therefore, it is to measure a certain displacement continuously for many times to obtain a group of N measured values, and make this group of measured values include a disturbance period, so as to obtain a measurement value that can represent the correct value. The structure of the signal shaping circuit includes a measurement operation expander and a photoelectric coupler; The function is to shape the measurement extended signal and send it to the computer. 89c4051 is the central part of the system hardware to realize digital processing. Its main frequency is 11.0592 MHz, including a peripheral reset circuit. It is mainly used to complete the functions of controlling a/d conversion, signal processing, sending data to the host and LCD in serial mode, etc. P3 port of single chip microcomputer is used as the control line of a/d conversion and communication. When reading the a/d conversion value, directly use the PI port to read the 12 bit a/d conversion value twice.

4. Parameter input correction circuit

The correction circuit is composed of max25c045, keyboard and selector switch. Its function is to adjust the zero position and full range of magnetoelastic displacement sensor, and to set the transmission speed of waveguide current pulse and store parameters.

5. Measuring parameter output circuit

The data output includes the 12bit high-speed d/a conversion chip max5302 and the measurement data of 0~5v, 0~10v, 0~10 Ma, 4~20 mA output from the operation expander; Binary data output includes 485 interface chip Max 1428 to output binary measurement data, and the data transmission distance can reach more than 1000m.

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