Probe Manufacturing And Control Circuit Design Of Thermal Anemometer

Thermal anemometer is an instrument for measuring fluid velocity, temperature, density and other parameters based on the principle of heat balance. The main working mode of anemometer is constant temperature type, whose speed measuring range is usually less than 300m/s, and unable to meet the requirements of hypersonic measurement. In this paper, we carried out the research of probe manufacturing and control circuit design of the thermal anemometer, which aims to lay the foundation for independently development of high performance thermal anemometer for hypersonic flow field measurement.Hot-wire, hot-film sensors and probes were designed and prepared firstly, then we carried out the experimental analysis. Results show that the sensors can be heated by electrical current and the resistance is sensitive to the flow, so it can meet the usage requirements of thermal anemometer.Then constant voltage and constant temperature probe control circuits were designed. In order to reduce the temperature sensitivity of the system, we designed the temperature acquisition and control program of the overheat resistance for the constant temperature thermal anemometer. From the calculation and analysis of the Wheatstone bridge circuit, hot-wire and the feedback circuit parameters, we presented the concrete method for the adjustment of the over-heat ratio, offset-voltage and the gain, which can avoid getting into the unstable operating region because of the improper adjustment for the measuring range and accuracy. Moreover, in order to improve the measuring bandwidth of the system, we designed the in-situ measurement circuit of the time constant and the T bridge compensation network for the constant voltage thermal anemometer.Data acquisition and control software of the thermal anemometer system was developed based on Labview and Presonal Daq 3000 module. The main functions include the data acquisition, gain and operation mode switch of the constant temperature thermal anemometer, parameters measurement of the sensor, calculating and setting of the offset voltage, it can meet the measure and test requirements of the constant temperature and constant voltage anemometer.Calibration experiments were conducted for the thermal anemometer system. Results show that measurement error of both the two type is less than 3% when the fluid velocity is in the range of 40~200m/s. The constant temperature type can meet different requirements of large scale or precision velocity measurement by adjusting the gain or overheat. By improving the power of the sensor, the measuring range of constant voltage type can be expanded to 300m/s.