A device for measurement of volume and leakage by pressure pulsation monitoring
N.P. Vaughan, R C Brown · Measurement Science and Technology · 1994
A novel device has been developed for measurement of both the volume and the extent of leakage from vessels, the latter being calculated in the form of the resistance of a leakage path. It consists of a small piston and cylinder capable of delivering a volume of air that varies sinusoidally with time, and a pressure monitor used to log the changes in pressure caused by the volume changes. The mechanism of action can be most easily understood by reference to an electrical analogue, in which it corresponds to an alternating current generator and voltage monitor used to measure capacitance (volume) and resistance (related to leakage) in parallel. The piston is operated at approximately 5 Hz and the data are logged at about 30 Hz. The parameters of interest can be computed from the amplitude and phase angle of the fogged voltage. The device can be used with a system experiencing an imposed airflow, provided that the frequency of this is far removed from that of either the piston or the logger. In this way it has been used to measure the leakage of respirators worn during breathing.