Design of oil filter control system based on microcomputer control

Design of oil filter control system based on microcomputer control

0 Introduction
    The system consists of one vacuum pump motor and one oil pump motor. It is required to use a single chip microcomputer to complete pipeline pressure detection and oil tank temperature control. The pressure sensor is used to collect data and send it to the single chip microcomputer for processing. The system uses two sets of heating tubes for heating, and the power of each set is 24 kW. The temperature sensor is used to collect data and send it to the single chip microcomputer for processing. When the temperature reaches the requirement, the vacuum pump motor is cut off and the current temperature value is displayed at any time. The contactor trip temperature can be set by the code dial and sent to the single chip microcomputer. The motor in the system can only rotate forward, not reverse, and the control circuit should have a reverse alarm device.
    The main circuit is realized by air switch and contactor, and the control circuit is realized by the single chip microcomputer control system. The system startup sequence is: oil pump motor, vacuum pump motor, heating tube. The two sets of heating tubes can be heated and stopped separately, but the heating tube can only start and run after the vacuum pump motor is started.

1 The main hardware of the control system consists of
    4 main circuit AC contactors, 2 air switches, MCS-51 series single-chip microcomputer chip 8031, various peripheral interface chips, A/D converter, temperature sensor, pressure sensor, photoelectric coupling device, contactor drive circuit, LED display circuit, etc. The control system is shown in Figure 1.

1.1 Input signal loop The basic composition of the temperature detection system
    is a digital temperature detection device composed of an integrated temperature sensor AD590 and a single-chip microcomputer. The AD590 temperature sensor is a semiconductor integrated temperature sensor with a measurement range of -55 to +150°C. The output current is linearly related to the temperature. It uses the zero point of the thermodynamic temperature scale as the zero output point, and the proportional factor is 1μA/°C. Therefore, it can convert the temperature signal into a current signal proportional to the absolute temperature. The sensor has high stability and good linearity. AD590 itself generates a current signal, which converts the temperature into a corresponding current signal output. An operational amplifier OP-07 is added to the output end of the sensor to convert its output current signal into a voltage signal.

The hardware circuit uses a dual-point temperature adjustment error, and the circuit is shown in Figure 2. The amplifier uses the OP-07 monolithic precision operational amplifier, which has the characteristics of low noise, low drift and high gain, and is a highly versatile operational amplifier. Capacitor C4 plays a filtering role here. A stable voltage is provided to the AD590 sensor through R1. The measured temperature is detected by the AD590 temperature sensor, and a voltage signal is provided to the voltage amplifier for amplification. Here, the potentiometer RP1 plays the role of adjusting the zero point, and the potentiometer RP2 plays the role of adjusting the gain. By adjusting the resistor RP1 and the potentiometer RP2 in the operational amplifier, the appropriate corresponding relationship between the output voltage and the measured temperature is found.

1.2 Basic composition of the output signal circuit
    This circuit is designed with AC electromagnetic contactor control, that is, the AC contactor KM coil is driven by a bidirectional thyristor. The rated working voltage is 2 to 3 times the working voltage of the AC contactor coil, and the rated working current is 1.5 to 2 times the working current of the AC contactor coil. Here, the AC voltage is 220 V, and a 10 A/660 V bidirectional thyristor is selected. The input terminal of the optical coupler MOC3041R is connected to 7407, and the P1.0 port of the single-chip microcomputer outputs a low level, the bidirectional thyristor is turned on, and the contactor KM is attracted. Otherwise, the contactor KM is released. Finally, the power circuit is controlled by the contacts of the AC contactor. The output signal circuit is shown in Figure 3.

3. Design of temperature detection program of control system
    The function of temperature detection program is to perform 4 A/D conversions continuously and obtain the average value of the conversion results. A/D conversion adopts query mode. To ensure the reliability of data, software filtering is performed by using mean filter method.
    The function of temperature control program is to compare the temperature detection value with the set value. If the detection value is greater than the set value by 2℃, one heating tube is turned off; if the detection value is greater than the set value by 5℃, two heating tubes are turned off; otherwise, no adjustment is made. If the detection value is less than the set value, heating tubes 1 and 2 are restarted to ensure continued heating. The A/D converter uses the AD0809 chip. Considering the convenience of calculation, debugging and programming, 00H~FFH corresponds to 0~5V and 0~128℃, that is, every time it corresponds to 1℃, the digital value is 02H, and the analog voltage is 0.039 V/℃. During debugging, when the temperature is 0℃, adjust RP1 to make the output voltage of the op amp 0 V, and the digital value after AD0809 conversion is 00H. When the temperature is 128℃, adjust RP2 to make the output voltage of the op amp 5V, and the digital value after AD0809 conversion is FFH.

4 Conclusion
    Compared with PLC control, this control system can detect, convert and display temperature without adding new circuits. It uses filtering technology in software algorithm design and optocoupler devices in hardware output circuit to achieve optoelectronic isolation and prevent arc interference during contactor closure. This control system has achieved good results in oil filter, produced good economic and social benefits, and has good promotion value.