Measuring and testing – Volumetric content measuring
Patent
1986-10-16
1987-12-22
Levy, Stewart J.
Measuring and testing
Volumetric content measuring
G01F 1700
Patent
active
047139668
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of measuring the volume of a gas in a container, and to an apparatus for carrying said method into effect, said apparatus comprising a tubular casing which is connected at one end to an opening in the container and in which a reciprocating wall is resiliently suspended, an excitation device, and a pressure gauge within said container.
One method of measuring the volume of a gas in a container is to utilize the general law of gases for adiabatic processes, which may be expressed as poxVo.sup..eta. =(po+.DELTA.P)x (Vo-.DELTA.V).sup..eta.. For closed containers, measuring presents no problem; it suffices to measure the pressure in the container at the volume sought, and then to change the container volume by a known amount, whereupon the pressure is measured again. However, many containers are not sealed but vented, and with such containers measuring is far more complicated. To be able to utilize the principle of the general law of gases, the pressure and the volume within the container must be changed such that venting does not affect the result, but a stable dynamic state may be achieved. This is accomplished by changing the volume and the pressure within the container at a frequency which is higher than the cut-off frequency of the low-pass filter formed by the venting duct.
U.S. Pat. No. 3,769,834 teaches a method of measuring the volume of an incompressible body enclosed within a container, by varying the volume of the gas surrounding the body in the container at a frequency between 1 and 100 Hz, and measuring the resultant change in pressure. This method has at least one great disadvantage: It requires a pressure gauge which is sensitive and accurate within a large pressure range. Such a pressure gauge is, of course, very expensive, thus making the entire measuring apparatus expensive.
An apparatus by which the volume can be measured without an expensive pressure gauge, is disclosed in FR No. 2,412,825. This apparatus comprises two containers interconnected by a membrane, one container housing the object whose volume is to be measured, and the other container being a reference container whose volume may be varied by displacement of a piston. On measurement, the pressure is varied uniformly in both containers, and the piston is controlled such that both containers are under the same pressure, the volume of the object being determined by the displacement of the piston. The disadvantage of this arrangement is obvious: The reference container makes the measurement apparatus very bulky and useless for large containers.
The above-mentioned disadvantages of an expensive pressure gauge and bulky reference container are found in all prior art apparatuses, even though they are designed in different ways.
It therefore is the object of the present invention to provide a novel measuring method permitting the volume of a gas in a vented container to be measured in a simple manner by means of a compact and inexpensive apparatus.
This object is achieved in that the container volume is varied according to a sine wave between a minimum and a maximum value, said variation being effected at a constant frequency but at a varying amplitude, in order to obtain a predetermined pressure difference (.DELTA.p); that the volume difference (.DELTA.V) corresponding to said predetermined pressure difference (.DELTA.p) is determined by detecting the points of time when at least two points on said sine wave are attained which correspond to two predetermined values of the container volume; that the time between the said two points on said sine wave is measured and used for calculating the maximum and the minimum value of the volume difference (.DELTA.V) corresponding to said predetermined pressure difference (.DELTA.p); and that the volume (V) is calculated on the basis of the formula V=.DELTA.Vxp.sub.0 x.eta./.DELTA.p wherein p.sub.0 =the static pressure and .eta.=Cp/Cv, wherein Cp and Cv are the specific heat capacity at, respectively, constant pressure and constant volume of the gas within th
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Derwent Abstract 830757 923/36.
Derwent Abstract 84-106 441/17.
Hesthamar Tore
Thyren Carl H.
Enpece AB
Levy Stewart J.
Raevis Robert R.
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