Electricity: measuring and testing – Conductor identification or location – Inaccessible
Patent
1985-05-23
1987-12-15
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Conductor identification or location
Inaccessible
324449, 324437, G01N 2722, G01N 3328
Patent
active
047136030
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an apparatus for measuring the fraction of gas in a two component fluid flow comprising a liquid and a gas in mixture, in particular a flowing oil/gas mixture.
BACKGROUND ART
The fraction of gas in a two component flow of liquid and gas may be defined as the volume of gas in an arbitrary section of a tube divided by the volume of that section of the tube. The fraction of gas may therefore be expressed as a number varying from zero (when the flow is entirely comprised by the liquid) to one (when the flow solely consists of gas).
While it has been of great importance to know how much of the production from an oil well is comprised by oil and how much of it is gas, measurement of the fraction of gas has always been considered with great interest within the offshore oil business.
Measuring devices whose operating principle is based on the detection of changes in capacitance, have been increasingly employmed for the measurement of the fraction of gas in two component fluid comprising liquid/gas mixtures.
The principle for such a measuring method is well known and amounts essentially to measuring the electrical capacitance across two electrodes, between which the mixture of the two components is flowing. If the area and the mutual separation of the electrodes are fixed, the measured capacitance will be related to the fraction of gas in the mixture between the electrodes.
By employing such a technique, it is in principle possible to build instruments with rapid dynamic response. The instrument may be constructed in such a way as to give a non-intrusive method of measurement. In spite of the advantage which is achievable in this manner, commercially available gas fraction meters based on the capacitance principle are relatively scarce.
The main disadvantage of known capacitance gas fraction meters is the dependence of the instrument calibration upon the nature of the flow regime being monitored. Thus, by example, the calibration curve required for a bubble flow will deviate from that of an stratified flow.
One of the reasons for this flow regime dependency is the missing homogenity of the electric field through the sample volume. If the electric field varies through the whole sample volume, the measured change in capacity which arises from a change in the gas fraction, will depend upon where the gas is located.
DISCLOSURE OF INVENTION
The object of the present invention is to remove these disadvantages and to provide a gas fraction meter of the above mentioned kind in which a homogeneous electric field is maintained within the sample-volume of the sensor. In addition it is also an object of the present invention to provide a non-intrusive measuring device of sturdy and simple construction, by which an output voltage proportional to the fraction of gas is generated by means of a simple signal processing circuit.
These objects are accomplished by designing an apparatus for the measurement of the fraction of gas in a two component fluid flow comprising a liquid and a gas in mixture, in particular a flowing oil/gas-mixture, said apparatus being based on the measurement of alterations of the electric capacitance across two electrodes (A, B) working at mutually different potentials, between which the two component mixture is forced to flow, which electrodes (A, B) form an integral paprt in a primary sensor, where the apparatus moreover includes a signal processing unit, characterized by comprising in addition to the said electrodes (A, B), a third electrode (C), which is arranged to be kept at a potential (V.sub.1 /2), which potential is at least approximately equal to the potential occuring half way between the other two electrodes (A, B), which third electrode (C) by example is fed by a simple voltage divider and a buffer amplifier (A.sub.2), whereby the signal processing unit preferably comprises a sine wave generator and a charge amplifier (amplifier with capacitance feedback) (A.sub.1). Besides being capable of fulfilling the above mentioned requirements, experiments
REFERENCES:
patent: 3254333 (1966-05-01), Baumoel
patent: 3339137 (1967-08-01), Perry
patent: 3375441 (1968-03-01), McBrayer
patent: 3450988 (1969-06-01), Breen
patent: 3879644 (1975-04-01), Maltby
Derwent's Abstract No. 94547 D/51, SU 813 234 (1979).
Dielectrical Measurements for Quantitative Analysis and Determination of Chemical Structures-Eme F.-Edited by Master of Science I. I. Zaslavski Publishing House "Khimiya" Moscow 1967-p. 68.
Den Norske Stats Oljeselskap A.S.
Eisenzopf Reinhard J.
Solis Jose M.
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