Temperature Effects of a Ceramic MEMS Thermal Wind Sensor Based on a Temperature-Balanced Mode

Abstract

A thermal wind sensor utilizes the fact that airflow over a heated plate will cool it asymmetrically, with the upstream part of the plate being cooled more than the downstream part. In the temperature-balanced (TB) mode, the heating power may be distributed spatially in the sensor such that any flow-induced temperature gradient is cancelled. Information about the airflow can be extracted in the distribution of heating power in the sensor. Ideally, the influence of changes in the ambient temperature on the sensor's output can be eliminated if in the whole measurement range the temperature sensor sensitivities are equal. However, because of the temperature dependency of the material properties of the airflow and the sensor, it may have a temperature drift. This paper, for the first time, investigates temperature effects of the ceramic microelectromechanical system (MEMS) thermal wind sensor based on the TB mode. The sensor consists of four outlying heaters and four inlying thermistors in two orthogonal directions on a ceramic substrate. When working in the TB mode, it could measure wind speed and wind direction by applying a power difference on the upstream and downstream heaters, so that the flow-induced temperature gradient is eliminated. Theoretical analysis has been developed which takes the variations of thermophysical properties in the sensor and the control circuits into account. Experiments for testing wind speed and direction have been performed in a wind tunnel with an adjustable ambient temperature. It shows that the wind speed is linearly influenced by the ambient temperature while the wind direction is inherently unaffected by ambient temperature variations. After compensation, the sensor shows a credible performance with an error of less than ±1m/s in wind speed and ±2° in wind direction in a temperature range from 0 °C to 30 °C.