Research Of Silicon Thermal Wind Sensor On Repeatability And Temperature Drift Characteristics

Recently, as the rapid development of semiconductor technology and desires for intelligent life, the applications of MEMS sensors have been popularized in more areas of life. Wind speed and direction information which are of great significance in wind speed sensors study are essential for daily life. In this paper, the two-dimensional thermal wind speed sensor which is based on silicon substrate is introduced. This kind of sensor are fabricated by CMOS-MEMS processing technology, namely do the bulk silicon process for MEMS, after completing the standard CMOS process. We discuss how to control the thermal wind speed sensor and the test data here, proposing some optimizations and improvement for the existing problems, thus end up with the test of high precision and wide-range output. The wind speed ranges from 0 to 40m/s, satisfying the requirement for precision of 0.5m/s±3%, while the wind direction ranges from 0 to 360°, with the precision error less than ±3°. The main work is as follows:(1) We study the theory of control system for the thermal wind sensor. Comparing the usual modes of constant power and temperature difference, we find the latter’s control circuit is more complicated, but has advantages on measure ranges over the former. The test way for heat temperature difference could have exact and stable output with low wind speed; also it works for two-dimensional wind speed measure, whereas with the sensibility decreasing for high wind speed while the hot-wire principle wouldn’t be confined to this. Therefore, we apply thermal field analysis to these two detections, and systemize their output signal and process circuits respectively.(2) We test and analyze the sensor chips and the whole sensor, finding out the consistency between the output and theoretical analysis for the calorimetric sensor, which means the sensibility and measuring range of the sensor are both restricted at high flow velocity. We propose an optimum proposal here, combing the calorimetric principle with hot-wire principle to conduct modes switch in different wind speed range. From the test results, we conclude that the optimized sensor system could achieve the wind speed and direction output with higher precision, which satisfies the weather specifications. Then, we discuss the repeatability of the sensor, finding that the sensor is stable with no hysteresis when the environment temperature is a constant.(3) Thermal wind speed sensor is sensitive to temperature, thus we do the analysis and compensation for sensor’s temperature drift. By theoretical analysis and experimental measurement, we find that the output of the sensor system has functional relationship with wind speed and temperature. Thus we could do temperature-rift compensation for the sensor’s output by setting up functional relationship. Moreover, an optimum proposal was raised up to compensate automatically in terms of hardware circuits, that is eliminating the temperature inconstant phenomenon between system chips and the environment by adjusting bridge circuit resistance to make the control circuits satisfying the coefficient matching equation. Consequently, we accomplish the compensation for output signals under CTD control method..