Methods for dynamic behavior improvement of tachometric and thermal anemometers by active control

Abstract

Tachometric and thermal anemometers are two types of instruments mainly used in typical standard measurements in meteorology, ventilation, air conditioning, technical and industrial measurements. Both types of these instruments have many beneficial metrological properties, which causes their widespread use in many measurement issues. However, the sensors of mechanical anemometers have large dimensions and considerable high mechanical inertia. This is the reason for their poor dynamic properties. This results in dynamic measurement errors that are the cause of the measured average value being normally overstated. Thermal anemometers are dedicated for measurements in fast-changing flows. Hot-wire constant-temperature anemometers due to the low thermal inertia of the sensor and the applied feedback, have a wide frequency bandwidth for velocity fluctuations measurement, reaching hundreds of kilohertz. For standard constant-temperature anemometers this bandwidth strongly depends on flow velocity. In high-amplitude fast-changing flows, this can cause significant dynamic measurement errors. This paper presents two methods for improving the dynamic behavior of respectively rotary and thermal anemometers by active control. These methods are based on the introduction of additional feedback loop to the instruments.