Measuring and testing – Volume or rate of flow – Using differential pressure
Patent
1981-02-17
1983-11-08
Goldstein, Herbert
Measuring and testing
Volume or rate of flow
Using differential pressure
7386152, G01F 138
Patent
active
044135300
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improvements made to gas flowrate measuring and monitoring devices, in particular devices with low flowrates.
2. Description of the Prior Art
Certain known devices use the deformation of two deformable chambers supplied with the same gas pressure higher than atmospheric pressure, to measure and monitor the gas flowrate.
In these devices, one of the chambers is supplied with said gas pressure through a flowrate restriction device, the flowrate of which is substantially the same order of magnitude as that to be measured. Moreover, this chamber can be placed in communication with the ambient atmosphere and hence with atmospheric pressure when the device is in the resting position, and in communication with the system of which the flowrate is to be measured, when the device is in the measuring position.
In the resting position, the pressure prevailing in the first chamber is the supply pressure, and the pressure in the second chamber is close to atmospheric pressure.
In the measuring position, the pressure prevailing in the first chamber remains equal to the supply pressure, and the pressure in the second chamber increases up to a value slightly less than the supply pressure; the difference in pressure results from the pressure loss experienced by the gas flow as it passes through the system whose flowrate is to be measured and hence depends on the flowrate of the latter.
Thus, it is the difference in pressure between the two chambers that enables the flowrate to be monitored to be measured and, for this purpose, deformation of these chambers is detected, which deformation can be amplified in any fashion--mechanically, electronically, or otherwise.
The drawback of this type of device resides in the fact that it has a relatively long response time, which is inherent in its very design, since the pressurized gas passes into the second chamber at the time of measurement through the flowrate restriction device. If a more precise measurement were to be made, the flowrate of the restriction device would have to be decreased by comparison with the flowrate to be measured, which would extend the response time even longer, while to cut down the response time a restriction device with a higher flowrate than the flowrate to be measured would have to be provided, in which case measurement would be less accurate.
SUMMARY OF THE INVENTION
The purpose of the present invention is to supply a device for measuring and monitoring low gas flowrates which has both a short response time and high sensitivity.
The device according to the invention has two deformable chambers, the first being solely and permanently in direct communication with a pressure source and the second being, on the one hand, permanently in communication with a source at the same pressure through a flowrate restriction device whose flowrate is substantially the same as the flowrate desired for the system to be monitored and, on the other hand, when the device is in the measuring position, in communication with the atmosphere through the system to be monitored, characterized by a valve being disposed on the gas path between the second chamber and the system to be monitored, said valve being closed when the device is in the resting position and open when the device is in the measuring or monitoring position.
The first advantage of such a device is the decrease in response time due essentially to the small differential between the resting and the measuring pressures. Because of this small differential, only a small volume of gas need be passed through the flowrate restriction device for the device to be set in the measuring configuration.
A second advantage, derived from the first, is that, because of its rapid response, a device according to the invention can be used continuously to monitor an adjustment operation while it is in process, as will be explained hereinbelow.
Other advantages will appear in the course of the description hereinbelow with regard to the attached dr
REFERENCES:
patent: 1653438 (1927-12-01), McLean
patent: 2867757 (1959-01-01), Wagner
patent: 3562782 (1971-02-01), Zychal
patent: 3621866 (1971-11-01), Thorsheim
patent: 4096746 (1978-06-01), Wilson et al.
Grossiord Claude R.
Guadagnin Laurent J.
Cricket Sarl
Goldstein Herbert
Shack Robert A.
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