Introduction

This paper is a discussion of a "black box" which, when attached to an existing orifice flow recorder, converts it into an integrating flow meter. It is produced in the form of a kit designed to be attached by the user to the various orifice meters commonly used in the field and in the plants [Figs. 1, 2 and 5]. This device opens up a whole new area in orifice flow measurement because it increases the accuracy of interpretation of orifice meter data by a factor of 10. The flow signal is converted into direct digital readout without the requirement of chart processing or planimetering. The device is battery powered so it may be installed in remote areas where power is not available. It will operate up to a year from a battery of two D-size flashlight cells.

LIMITATIONS OF THE CHART SYSTEM

For the past 10 years, flow measurement engineers have been searching for a better way to measure flow of fluids, particularly gas. The search has been for a higher level of measurement accuracy together with a means of reducing the cost involved in flow measurement. In the course of this search, measurement engineers have explored the possibility of using types of measurement apparatus really quite foreign to oilfield usage. Granted, the venerable orifice meter, which has been with us for about 50 years, has appeared to be incapable of meeting the accuracy requirements called for by modern petrochemical technology. May be some new and strange device could fulfill this need. However, as one looks more carefully at the problem of flow measurement with the orifice meter, does the problem really lie with the basic principle of the device? A monumental amount of work has gone into the collection of experimental data for converting differential pressure information into meaningful flow measurement coefficients. Similarly, differential pressure and static-pressure-sensing elements have been brought to a high decree of perfection. Certainly, it is no problem to determine meter-tube and orifice-plate diameters with accuracy. Chart drives with a tuning accuracy of better than 1/4 per cent are available. Where, then, lies the problem?

The Achilles heel of the orifice meter lies in the generation and interpretation off the chart record itself. By the elimination of this weakness, the orifice flow meter can once again take its deserved place at the head of all flow-measuring equipment. As will be shown, the Kingmann-White Flow Integrator eliminates that weakness from orifice meter measurement.

To the experienced gas-flow measurement engineer, the statement that the limitation of the accuracy of the orifice meter lies primarily with the chart system comes as no surprise. However, the magnitude of the inaccuracy often is more than a little shocking to him. While it is true the Integrator has shown up some rather dramatic and startling errors in chart interpretation, studies made some years ago, before it was available, gave even then incontrovertible proof of the problems that exist in interpretation of chart records.

A west coast gas measurement engineer, L. J. Kemp, made an extensive and intensive study of the question of how accurately it is possible routinely to process or planimeter charts taken from orifice flow recorders. Using a mechanical integrator, he artificially created 20 different chart patterns. Consequently, he knew the correct result of planimetering each chart. These charts were then produced by a printing press in quantity in two colors. Packets of these charts were sent to many different companies throughout the United States who routinely process gas-flow charts. Included were gas companies, oil companies, utility companies and the like. The recipients were asked to process the charts in their normal fashion and return the packets indicating the flow units for each chart and the length of time required to do the processing. The results were classified and studied. His findings have been presented before several technical societies. Table 1 show the results in simplified form.

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