Measuring and testing – Instrument proving or calibrating – Volume of flow – speed of flow – volume rate of flow – or mass...
Patent
1994-05-05
1995-10-31
Chilcot, Jr., Richard E.
Measuring and testing
Instrument proving or calibrating
Volume of flow, speed of flow, volume rate of flow, or mass...
73 4V, G01L 2700
Patent
active
054619017
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a testing apparatus for in situ calibration of pressure gauges, comprising a reference chamber for connection of the pressure gauge to be tested, a calibrated pressure sensor connected to the reference chamber, and a regulating means connected to a gas supply unit and arranged to regulate the pressure in the reference chamber.
Current fields of use of such an apparatus are e.g. control of altimeters in aircrafts and control of pressure gauges which are used to measure gas deliveries for production platforms for hydrocarbons. The pressure gauges may be constructed to measure absolute pressure, manometric pressure or differential pressure.
According to what one knows, there has not been developed mobile equipment having sufficient precision and stability to operate in the field for control/calibration of high-precision pressure gauges. Thus, common practice is to disassemble the pressure gauges at given time intervals and send these to a laboratory for a fresh control/calibration (with e.g. a "dead weight tester"). This circumstantial procedure is a natural consequence of the fact that, outside specially equipped laboratories, it is difficult to procure relevant test conditions.
One has tried various solutions with respect to procuring acceptable conditions for pressure calibration at the place of use. One has, for example, connected the pressure gauge in question and a precision pressure sensor to a common chamber of which the pressure may be regulated by means of a movable piston. It has, however, appeared to be difficult to obtain the pressure stability over time which is necessary, because even very small gas leakages or temperature changes have influence on the calibration (i.e. the pressure). Traditional pressure regulators neither has shown to be suitable in this context since the degree of regulation is too small.
SUMMARY OF THE INVENTION
Thus, the object of the invention is to provide a testing apparatus having such a high degree of regulation that the calibration can be carried out with an accuracy in the pascal region, even with line pressures up to 200 bars (200.multidot.10.sup.5 pascal).
The above-mentioned object is achieved with a testing apparatus of the introductorily stated type which, according to the invention, is characterized in that the regulating means comprises a gas flow balancing means connected to the reference chamber and arranged to create a balance between supply of gas to and delivery of gas from the chamber, and a first and a second pressure regulator connected to an inlet and an outlet, respectively, from the flow balancing means and controlled by a feedback signal from the reference chamber, so that the first regulator sees that the pressure at the inlet of said means at any time is a little higher than the pressure of the reference chamber, and the second regulator sees that the pressure at the outlet at any time is a little lower than the pressure of the reference chamber, the flow balancing means being adjustable under the influence of an output signal from an electronic control circuit having a first input for supply of the output signal from the calibrated pressure sensor, and having a second input for supply of a reference signal.
In use of the apparatus this is provided with a valve means isolating the pressure gauge in question from its original measuring point and instead connecting it to the reference chamber of which the pressure may be regulated in a stepless manner and stabilized at any chosen value. Thus, one can in a simple manner, without removing the pressure gauge, test its accuracy within the functional region of interest.
In the testing apparatus according to the invention, relevant test conditions are obtained by means of the gas flow balancing means which provides for the provision of the desired pressure in the reference chamber by creating a balance between supply and delivery of gas. The desired degree of regulation is obtained in that supply and delivery of gas take place through a pair of pr
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Derwent's Abstract No. 83-710775/28, SU 957 024, Publ. Week 8328, Kuzmin VV.
Chilcot Jr. Richard E.
Felber Joseph L.
Ottestad Breathing Systems AS
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