METHOD AND DEVICE FOR MONITORING OF A GAS FLOW, IN PARTICULAR OF A NATURAL-GAS FLOW

摘要

Method and device for monitoring of the composition of a flowing gas. An oscillation of sound frequency is applied to the gas flow pipe (10) downstream and upstream, and the travel times (t1, t2) of the monitoring sound over a certain measurement distance (L) downstream and upstream are detected. The sound speed (c) or a quantity representing same is determined on the basis of said travel times (t1, t2). This speed (c) is mainly dependent on the average molecular weight of the gas to be monitored. The temperature (T) of the flowing gas is measured, and on the basis of the measurement of temperature, the sound speed that has been reduced to a certain reference temperature T0 is determined from the formula c0 = c . 2ROOT (T0/T), which is applicable to an ideal gas and wherein T = absolute measured temperature of the gas, T0 = chosen absolute reference temperature, c = measured sound speed, and c0 = sound speed reduced to the reference temperature, or by using a corresponding more realistic formula. When the reduced temperature (c0) differs from its range of expected values (c1...c2), an alarm signal or control signal is given. Alternatively, the limits (C1, C2) of the range of expected values can be reduced to temperature.