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Title: The Ac-Me Recording Gravitometer
Author: H. F. Goodenough
Source: 1938 Southwestern Gas Measurement Short Course (Now called ISHM)
Year Published: 1938
Abstract: rpHE EFFECT of the specific gravity on the measurement of the gas through an orifice meter is taken into account when calculating the coefficient. To determine the importance of the gravity in this connection, consider the coiTection factors for different gravities. For example, when using a gravity base of .60, the correction factor for a specific gravity of .59 is 1.0084 and the correction factor for a specific gravity of .61 Is .9918. From these two correction factors it is indicated that a difference of .01 in the specific gravity of the gas will make a difference in delivery of almost one per cent. When the specific gravity of a gas remains reasonably constant over a period of time, the specific gravity gas balance is the proper instrument to use in determining the specific gravity of the gas for correction purposes. Periodic tests are made at intervals suitable to the conditions. On the other hand, when it is known that the specific gravity of the gas does not remain constant during the period, a continuous record of the specific gravity is necessary for obtaining the correct flow. The record of the specific gravity for any period is used to correct the orifice meter measurement for the same period. When it is realized how the specific gravity changes under some conditions, it becomes apparent that the gravity record is of importance to the accurate measurement of gas by an orifice meter. Figure 1 is a reproduction of a chart from an Ac-Me Kecordmg Gravitometer which illustrates variations in specific gravity that are sometimes encountered. In this particular instance, the installation was made in a city gate measuring station. The cause for the variation in specific gravity was the fact that the gas being measured was made up of natural gas from two separate sources.

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