New approch to the control and measurement of small gaseous nlass flow rate is
needed when the mass flow rate is too small to be measured by traditional flow meter．In this paper，
the background and principle of the instrumentation system for small gaseous mass flow rate measurement
are presented．The instrumentation system were set up．Two means，namely，the small mass
flow rate measurement by tandem arranged orifice plate and mass flow rate meter，and small mass
flow rate measurement with orifice plate and differential pressure were tested．Different fitting equations
were obtained．The accuracy and characteristics of the two methods were also compared．The
results show that the second method has reasonable repeatability and the accuracy has improved effeetively．