The Development Of A Portable Thermal Anemometer With High Performance

As frequently used instruments in measuring flow velocity, portable thermal anemometers, whose common control method is the constant-temperature control mode, have the disadvantage in both measuring range and speed, which means it cannot full fill the requirement for high speed and continuously measuring. To expand the measuring range and speed of a thermal anemometer, this paper presents a portable thermal anemometer whose control method is based on constant-voltage control.After analyzing the working principles and dynamic characteristics of the constant voltage anemometer(CVA), a portable constant voltage thermal anemometer is proposed. The designed anemometer can realize a wider range and continuous wind velocity measuring. Meanwhile, it can measure flow temperature. Besides its portable size, it can be battery powered and has both display and storage function, together with a communication interface with a host computer.Based on the proposed design scheme, detailed designs in hardware and software for anemometer are presented. The core to anemometer's hardware is an ARM processor, based on which the control circuit for probe, time-constant in-situ measuring circuit, T-bridge compensating circuit, data acquisition circuit, gain control circuit and communication circuit are presented with detailed description. As for software designing, units as data acquisition and processing and the design of human-computer interface are emphasized.At last, verification for designed anemometer based on tests is carried out. A calibrating system is established to provide a stable flow field, and then the calibrating experiments are conducted. Firstly, parameters of the bias amplification circuit are determined. After which, the dynamic calibration is introduced to test the measuring range and to acquire the correspondence between the wind velocity and the output voltage. Finally, data fitting and error analysis are conducted. The results show that the designed CVA system is able to measure a velocity up to 300m/s and has a measuring frequency of 50 times per second with measuring error less than 3%.