GB982147A - Improvements in or relating to hot wire anemometers - Google Patents

Abstract

982,147. Measuring electrically. NATIONAL RESEARCH DEVELOPMENT CORPORATION. July 20, 1962 [July 20, 1961], No. 26292/61. Heading G1N. [Also in Division H3] In a hot wire anemometer capable of measuring rapid variations in air velocity, the amplitude of oscillation of a H.F. carrier is representative of the velocity of the air-stream past the hot wire. As shown, Fig. 3, a bridge comprising a hot wire RW, e.g. a 0.0001 inch etched platinum wire, and a variable comparison resistor RO, is supplied by a transformer T1 whose primary winding is tuned by a capacitor to resonate at a frequency of hundreds of kc./s. The output from the bridge is fed via an amplifier, a stabilizing network, and a power-amplifer, back to the primary of T1. The air velocity analogue signal is taken from across the transformer secondary to a demodulating circuit. In Fig. 2, the output from the hot wire bridge AMC is fed via a capacitor CS to a 2-stage error amplifier AMD and thence to a push-pull output stage PP which is connected to the tuned primary of ferritecored transformer OTR. H.F. carrier amplitude is stabilized by a fast-acting, non-linear stabilizing circuit STC loading the transformer. Alternatively, stabilization is obtained by modification of the feedback circuit of the error amplifier, Figs. 4, 5 (not shown). Fig. 6 (not shown) depicts an amplifier, the output stage of which is arranged to provide connection to alternative linear and non- linear stabilizing units. Transistor circuits may be used.