Design and simulation analysis of a digitally controlled constant temperature hot wire anemometer

The hot wire anemometer has been used for many years as an effective instrument for measuring average and turbulent wind velocities. Since the hot wire anemometer is a thermal transducer, it is a rather complicated instrument. The wire has thermal inertia with an associated time constant. The electronic circuitry has its own time constants and there are complex interactions involved between the wire and the circuitry. The wire is a non-linear device and this nonlinearity causes further complications, particularly in the control and calibration procedures.

In this study, an effort has been made to develop and analyze a new technique for making hot wire anemometer measurements. This is a digitally controlled hot wire anemometer which permits automatic setting of the operating point any time 9 desired. The technique is based on the constant temperature mode in which the resistance of the wire is kept constant. Analog-to-digital and digital-to-analog converters are used with a digital signal processor and variable current source to set the resistance at the operating point and to compensate for the changes in the cooling effect of the flow, thus maintaining a constant probe resistance.

The main features of this approach are ease of calibration and operation and the versatility inherent when changes in operation can be made with software rather than hardware modifications. A proposed hardware implementation of the technique is given and, through computer simulation, is evaluated.