Interpretations in the control theory of thermal anemometers

Abstract

The cut-off frequency, or frequency range, of a dynamically optimized constant temperature hot-wire anemometer is well known in terms of time constants of the wire and of the feedback amplifier, within the framework of a linear control theory of third order. A more convenient interpretation, in terms of a characteristic frequency of the wire and in terms of gain-bandwidths products of the amplifier, is presented both for an amplifier with a second-order response and for an amplifier with a first-order response. These convenient and intuitively appealing interpretations are also extended to hot-film anemometers.