Principle of digital inclinometer

For the inclination of the horizontal position, the parallelism and perpendicularity of the two components, the straightness of the machine tool, the instrument guide rail, the flatness of the table, and the flatness of the flat plate have a very broad application prospect.

The inclination sensor in the design is a tilting sensor based on thermal convection. The inclination sensor is small in mass, and the inertial force generated during large impact or high overload is also small. Therefore, it has a strong anti-vibration or impact capability. It is one of the tilt sensors that combines the advantages of simple structure, high reliability, and general-purpose sensor integrated circuits. The design measures the inclination of the platform by the inclination sensor, and outputs the voltage signal. After the amplifier is amplified, it is output to the single-chip circuit for data processing. After the Zui, the dip angle is displayed by the digital tube, and can also be used as the control system output control signal adjustment platform. inclination.

1 Principle of digital inclinometer

The overall hardware design principle of the inclinometer is shown in Figure 1. It consists of sensors, preamplifier circuits, A/D converter circuits, and microcontroller systems. The sensor collects the acceleration information and outputs the voltage value after internal conversion. The voltage value is divided into two paths, one is to measure the acceleration in the X-axis direction, and the other is to measure the acceleration in the Y-axis direction. The two voltage signals are subjected to low-pass filtering and operational amplifier amplification processing, and then the amplified voltage is output to the A/D conversion module, and the A/D conversion module outputs 8-bit digital quantity for processing by the single-chip microcomputer, and the serial data is output after the single-chip microcomputer Zui The digital tube displays the tilt angle of the output platform of the circuit.

2 How the sensor works

The sensor used in the design is the MXA2050A, which is a complete accelerometer system on a monolithic integrated circuit CMOS IC. The sensor is based on natural convection for heat conduction. In MXA2050A, the gas is the only moving body in the sealed cavity. Its mass is small, and the inertial force generated during large impact or high overload is also small. Therefore, it has strong Resistance to vibration or shock. It is an extremely inexpensive dual-axis accelerometer that is particularly reliable because it does not have moving parts, and can be manufactured using a sub-micron CMOS method. This method can produce small-sized wafers, so the device is very inexpensive and versatile. The MXA2050A acceleration measurement range is: ±10gn, and the output is two analog voltage signals. Allows resolution of less than 10 mg in a 1 Hz bandwidth. Signal, frequency response can be extended to 40Hz. With a simple external circuit, the frequency response is extended to 160 Hz.

The thermal convection accelerometer comprises a closed cavity filled with fluid, wherein a heating element heats the fluid surrounding the heating element in the cavity, and the heated fluid expands and the density decreases, under the action of gravity. Ascending, the surrounding relatively cold fluid is replenished to the empty position, thus repeatedly cycling to cause heat convection conduction. In the static state, the temperature curve is symmetrical. In the case of acceleration, due to the natural convection heat conduction, the acceleration in any direction disturbs the temperature, causing temperature asymmetry. Therefore, the temperature and output voltage of the four thermopiles in the accelerometer are different. Different thermopile output voltages are directly proportional to acceleration. They have 2 identical acceleration signal channels on the accelerometer. One is to measure the acceleration in the X-axis direction; the other is to measure the acceleration in the Y-axis direction, and its peripheral circuit is shown in Figure 2.

3 op amp, A / D conversion and display circuit

In the application of the sensor, the high-impedance preamplifier mainly has two functions: one is to amplify the weak signal of the sensor; the other is to convert the high-impedance output of the sensor into a low-impedance output, and the preamplifier in the design is mainly by document .write('') AD623document.write('') Amplifies the circuit composition, the circuit diagram is shown in Figure 3.

The op amp document.write('') AD623document.write('') can also implement the functions of subtraction, addition and amplification. The signal output from the sensor VX is first subtracted from the zero voltage in the horizontal direction, and then amplified. Times, plus the reference voltage VREF, after the output of zui is

The amplification factor can be adjusted by adjusting the size of RG1, and the reference voltage is divided and output by the sliding varistor. The voltage signal generated by the sensor is first passed through the amplifier and output to the A/D conversion circuit. A/D conversion uses document.write('') TLC5510document.write('') , which can realize the conversion speed controlled by the single-chip microcomputer. The output digital quantity is 8 bits, which can realize the design precision requirement.

The display circuit is mainly composed of two parts: a shift register and a digital tube display. The data processed by the single chip is converted into serial format data, and the shift display is realized by the shift register under the action of the clock signal. The display circuit uses a total of 8 shift registers, 8 digital tubes, respectively, to achieve 4-bit angle display in the x, y direction, accurate to 0.01 °. The shift display circuit is shown in Figure 4.

4 Experimental results and data processing

In the process of experimental data processing, multiple sets of data are measured, and the arithmetic mean is obtained as the result measured after zui. Therefore, the uncertainty of the arithmetic mean must be studied. If multiple series of repeated measurements are made for the same magnitude under the same conditions, each series of measurements has an arithmetic mean. Due to the existence of random errors, the arithmetic mean of each measurement column is also different, and they are measured around The true value has a certain dispersion, this dispersion shows the uncertainty of the arithmetic mean, and the standard deviation σ of the arithmetic mean is a parameter that characterizes the dispersion of the arithmetic mean of the individual measured columns of the same measurement, and can be used as an arithmetic. The * standard for the uncertainty of the mean. The arithmetic mean x is known to be

It can be seen that in the equal-precision measurement column of n measurements, the standard deviation of the arithmetic mean is a single measurement standard deviation. When the measurement number n is larger, the arithmetic mean is closer to the measured true value, and the measurement accuracy is obtained. The higher. Increasing the number of measurements can improve the measurement accuracy. However, it can be seen from the above equation that the measurement accuracy is inversely proportional to the square root of the number of measurements. Therefore, it is necessary to pay a lot of labor to significantly improve the measurement accuracy. Practice has also shown that after n>10, σ-x has been reduced very slowly. In addition, because the number of measurements is larger, it is more difficult to ensure that the measurement conditions are constant, and new errors may be introduced. In general, n=10. Therefore, in the experiment, the arithmetic mean of the measurement results of 10 times was taken as the measurement result after zui. The voltage dip relationship curve after measurement is shown in Fig. 5 and Fig. 6.

5 Conclusion

In order to meet the market demand of machinery manufacturing, equipment installation, road and bridge, construction engineering and other industries and export, a digital display inclination measuring instrument based on acceleration sensor is designed, which has a resolution of 0.01° and a comprehensive precision of 0.03°. Product level; cost-effective. It has a wide range of applications in surveying instruments, construction machinery, antenna positioning, robotics, tank and ship artillery platform control, aircraft attitude, automotive electronic control, oil exploration, and offshore platform monitoring.

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