GB1439324A - Gas flow measurements - Google Patents

Abstract

1439324 Measuring gas velocity BRITISH STEEL CORP 16 Oct 1973 [17 Oct 1972] 17627/72 Heading G1A The mean velocity of a gas, e.g. the effluent from a steelmaking vessel, is measured by detecting emitted radiation at two points spaced along the flow or determining the delay to the upstream signal necessary to produce maximum correlation between the waveforms. As shown, Fig. 1, the gas flow through a pipe 1 is monitored by two I.R. pyrometers 2, 3 (e.g. PbS photo-conductors) having narrow fields of view which lie in parallel planes but are inclined to one another so as to define a restricted axial path in the gas along which correlation exists and the velocity is determined. The detector signals are passed through identical filters 4 which may be high, low or band-pass selected in accordance with the emission characteristics of the gas and the measurement mode used. The upstream signal is passed through a variable delay network 6 and a circuit 7 derives the correlation junction, the maximum value of which is attained when the delay introduced by network 6 is equal to the 'time of flight' of the gas between the two pyrometers. A circuit 8 calculates and displays the velocity of the gas. For certain applications fast acting AGC amplifiers 4A may be introduced into the signal channels. One or both pyrometers may be mounted for pivotal movement within the crosssectional plane of the pipe in order to scan the effective measurement axis across the pipe to obtain a velocity profile.