A constant-temperature anemometer (CTA) with a means of eliminating the effects of cable resistance on the probe overheat ratio

Author: P. Ligeza

Measurements of flow velocity are an important step in the control of the air ventilation conditions in mines and ventilation processes.

As metrological conditions prevailing in such situations are very specific and measurements may serve different purposes, several methods of gas flow velocity measurements have been developed to meet the needs of the mining sector.

This paper examines the possible applications of hot wire anemometry to obtain measurements of velocity fields in fast--changing gas flows. The suggested solution of a CTA may be applied both in laboratory tests and in flow measurements in mines.

The major advantage of the device is that the effects of cable resistance on the wire overheating ratio are wholly eliminated. The measuring sensor may be used in places where the distance between the sensor and the measuring apparatus is considerable and when cable resistance may vary due to ambient temperature variations.

A classical configuration for the operation of a hot-wire anemometer is the constant-temperature bridge circuit, where the resistance of the sensor-supplying cable affects the overheating ratio. This may lead to measurement errors. In order to eliminate those shortcomings, a new CTA circuit for supplying the hot wire anemometer was developed, which permits four-point measurements of the sensor resistance.

The effects of cables and junction resistances on the wire overheating ratio are thus eliminated. The dynamic parameters are similar to those of the typical bridge circuit. In several metrological applications this circuit may prove to be an excellent alternative to traditional solutions.

The paper examines the structure and the operating principles of the new circuit, presenting also the results of modelling and experimental tests.