Fundamentals and trends of digital measurement

The resolution of the three-dimensional character of flows using hot-wire/film techniques can be achieved using either single or multiple sensors. Usually, the anemometer response is measured in an unknown flow field, and with predetermined probe calibration data and known directional characteristics, the flow field can be determined. This paper introduces a method capable of predicting the constant-temperature anemometer response of any single wire or film probe in a known flow field. The method is also capable of predicting the probe response at any orientation once the response is known at another orientation. This method will prove particularly useful for checking probe calibration especially if drift is suspected. Voltage drift can be caused by a variety of problems including dirt and bubble formation on the sensor as well as probe aing. Having a mechanism to keep track of the signal will prove extremely useful in identifying external causes of voltage drift. The analysis presented in this paper provides such a mechanism and is shown to be valid for both the linearized and unlinearized signals. The validity of the analysis has been demonstrated by carrying out measurements in a water channel and at the axis of a circular pipe. © 1999 Elsevier Science Ltd. All rights reserved.