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Title: Auxiliary Measuring Devices
Author: H. V. Beck
Source: 1945 Southwestern Gas Measurement Short Course (Now called ISHM)
Year Published: 1945
Abstract: In the measurement of gas, two general methods are employed measurement by displacement meters and measurement by orifice meters. Each method has its advantages and disadvantages. With positive displacement meters, the measurement is automatically limited to those pressures which a meter case will stand which in most instances would be something less than 500 lb. gauge. Furthermore, the size of the meter is quite large relative to the amount of gas measured. It has the distinct advantage, however, that measurement can be made down to extremely low rates of flow. With the orifice meter, quite the reverse is true measurement can be made at pressures up to 5000 lb. gauge, and flow can be measured at rates as high as the carrying capacity of the pipe line with apparatus of relatively small size. The orifice meter is limited, however, by its inability to measure flow accurately at low rates-the range of accurate measurement being in the neighborhood of 3 1/2 to 1 This limitation is a fundamental one since it results from the fact that measurement is obtained from the orifice differential pressure which varies as the square of the rate of flow for example, with a range of flow of 3 and one half to 1, the differential will vary from about 12 to 1. At one-twelfth of the maximum differential, there are inevitable errors in reading the chart which would consequently limit the accuracy which could be expected.

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