Measuring and testing – Fluid pressure gauge – Electrical
Patent
1978-11-22
1980-04-15
Woodiel, Donald O.
Measuring and testing
Fluid pressure gauge
Electrical
G01L 2112
Patent
active
041977521
ABSTRACT:
In the thermal gas pressure gauge, a foil heater has a heater surface disposed in gas communication with the gas to be measured and the heater surface is thermally cycled at first and second reference frequencies to produce cyclical heating of the gaseous material adjacent the heating element. A directional microphone is disposed facing the heating element to derive signals of an amplitude determined by the amplitude of the cyclical heating effect of the gaseous material at the first and second reference frequencies. The detected signals are synchronously detected to produce a pair of dc outputs indicative of pressure in two respective pressure regimes. In an overlap pressure regime the two dc outputs are converted to digital signals which are correlated with pairs of values tabled in a read only memory for reading out a digital signal indicative of the pressure. In a low pressure regime from approximately 10.sup.-4 torr and below to the region of 1 to 10 torr, the measured pressure is independent of the molecular gas species and therefore is an absolute gauge, whereas in the higher pressure regime from 1 to 10 torr to the condensation pressure of the measured gas, the measured pressure is somewhat dependent on the molecular gas species. For measurement in the higher pressure regime, the heater and microphone are contained within a volume of the gas separated from the relatively large volume of a chamber being measured by means of an acoustic filter. The acoustic filter provides a high impedence to pressure waves at the second or higher reference frequency to avoid dissipation of the generated pressure wave to be measured within the large chamber volume. The tabled values in the read only memory permit a smooth transition of the gauge measurement from the first to the second regime.
REFERENCES:
patent: 3199356 (1965-08-01), Andriulis
Aine Harry E.
Lowhurst Harvey G.
Woodiel Donald O.
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