Abstract
A self-adaptive instrument servomechanism has been devised to enable airflow direction to be automatically determined when using a hot wire anemometer for flow measurements. In the anemometer, used for measuring air velocity and turbulence, a fine wire acts as the sensing element. The wire is maintained at constant temperature by an automatically balancing bridge circuit, the voltage across which is a measure of the rate at which the flow is cooling the wire. When the probe from such an instrument is rotated through 360° in an air stream the voltage/angle characteristic is as shown in Fig. 1; with the wire axis along the flow direction the bridge voltage is a well-defined minimum while a less definite maximum voltage is obtained with the wire normal to the flow. Location of the successive minima or maxima is achieved by a hill-climbing method.
The device has been developed for taking measurements in two dimensional flow within the rotors of certain fans where difficulties of access preclude the use of any probe having a large head.
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