Practical considerations for validity of constant temperature anemometer flow measurements in industrial applications

The constant temperature anemometer (CTA) is used for measurement of flow characteristics in turbulent flow regions. Factors such as ambient conditions and contamination of the CTA sensor strongly affect the working of CTA, and its nonlinear calibration curve to a lesser extent. In order to minimize the consequences of these factors, the CTA must be recalibrated from time to time. For research applications, the recalibration can be done prior to each measurement. However, frequent recalibration is time consuming and expensive, and may be impractical in medical and industrial applications. In this paper, the use of CTA as flowmeter has been considered in the latter applications. To keep the need for elaborate recalibration of the CTA used as flowmeter to minimum, practical guidelines for ascertaining the validity of flow measurements have been presented. Application of correction factors for improvement of measurement accuracy has been discussed. Effect of change in the CTA voltage offset on the measurements has been considered. Results show that although correction factors can be used to improve the accuracy of measurements by the CTA used as flowmeter, in some cases, application of a correction factor alone cannot improve measurements, and thus recalibration of the CTA becomes necessary. Also, the use of correction factor alone does not allow for extension of measurements by the CTA used as flowmeter beyond its calibration range.