The single-chip microcomputer measurement and control module in the embedded vacuum controller is based on the 89C51 microcontroller, five 24-bit A/D converters (AD7714), two 12-bit D/A converters (TLC5616), RS485 (MAX485) interfaces, and liquid crystal Display (including IO) and other components. The thermocouple regulator (DL-3) was used as a vacuum measuring sensor of 10 to 0.1 Pa, and the thermocouple regulator (DL-3) was used as a thermocouple.
The constant current source circuit provides operating current for the thermocouple regulator, and the microcontroller analog output voltage controls the constant current source current. The thermocouple regulation works in the constant current mode, and the single-chip closed-loop control thermocouple regulates the operating current to ensure the current stability. The thermocouple potential is measured in real time and transmitted to the PC. The PC performs the nonlinear calibration, vacuum calculation, calibration, and measurement range selection of the thermocouple regulator.
The MCU first uses the thermocouple regulator to measure the vacuum degree of the GM refrigerator. When the pressure is less than 1×10-1Pa, it automatically switches to the ionization gauge. When the pressure is stronger than 1×10-1Pa, it automatically cuts off the ionization gauge power supply. And give alarm tips to protect the ionization gauge. When the GM refrigerator is turned on, when the vacuum degree reaches 10-3 Pa for the first time, the ionization gauge tube is automatically degassed, and the degassing time is set by the PC through serial communication (1 to 5 minutes). The protection of the tube is to monitor its current and control its current to be less than 150mA.
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