The Design Of Ultrasonic Gas Flowmeter Calibration Test Bench

For the past few years, with plenty of promotion and application of ultrasonic gas flowmeter, how to improve its stability and reliability has become a focus of concern for manufacturers. By employing the method of automatic control, ultrasonic gas flowmeter calibration test bench generates standard environment and conditions for the calibration,maintains stability of gas pressure and flow for the calibration, makes a powerful guarantee to boost the quality of the ultrasonic gas flowmeter.This thesis proceeded from the whole structure and working principle of ultrasonic gas flowmeter calibration test bench, designed the system composing scheme. According to the existing system design, this dissertation constructed the hardware circuits of ultrasonic gas flowmeter calibration test bench constituting the main control circuit, the controlled circuits of pressure and flow, the communication circuit and the filter circuit, analysed parts selection and performance matching of each modular circuit, realized the circuit design from the controller with the MPU as the core to the controlled object, from the sensor to the amplifier and filter then returning to the MPU to A/D sampling, finally, sent the data collected by the communication circuit to the computer. This thesis designed the software implementation scheme in terms of the corresponding circuit. In this dissertation, the control algorithms of the calibration test bench was deeply discussed, made a concrete analysis of membership function, fuzzy control rules and the process of defuzzification of fuzzy PID algorithm combining with control object. For the coupling problem between pressure and flow, this thesis devised a reasonable control strategy based on calculated coupling degree and actual test data. This thesis realized controlling the pump speed with fuzzy PID algorithm, at the same time, controlled the turning angle of stepper motor to regulate valve position with PID algorithm. The calibration test bench can not only control the speed of pump but also adjust the position of valve and implements control requirements in different pressure and flow. It also designs monitoring interface in the PC to realize communication transfer. The calibration test bench achieves the automatic adjustment of each required pressure and flow and provides a standard flow as reference to calibration.This dissertation drew charts of pressure data and flow data receiving from the computer of undecoupled system and decoupled system. Then the chats showed that the control of pressure and flow after decoupling was more stable and eliminated interference factors. Finally, the experimental results indicates that the ultrasonic gas flowmeter calibration test bench can realize stable control of pressure and flow, the indexes of static performance and dynamic performance all accord with the anticipated requirement.