This section describes various types of instrumentation used inthe practical application of basic gas laws to metering. Includedare chart recorders of various types associated with distributionmetering, meter-mounted correction devices, pulse transmitters(other than remote reading) and load survey equipment.
A diaphragm, rotary or turbine meter measures gas at theconditions of pressure and temperature existing as the gas flowsthrough the meter. It is this volume that is indicated on theconventional-type index normally found on the meter. Since gas ispurchased and sold at certain specific base conditions of pressureand temperature, it is necessary that when measurement is atconditions other than these, a means must be provided forcorrecting the volume as measured, back to these baseconditions.
There are several common methods used to accomplish this. One ofthese involves the use of chart recorders on which the variation inpressure and/or temperature and time are documented. A visualrecord is generated from which, by manual or mechanical methods,corrections to the uncorrected volume can be made. A second methodinvolves the use of devices capable of mechanically introducing acorrection factor based on Boyle's Law with respect to pressureand/or Charles' Law when temperature variations are involved. Sincenatural gas is a mixture of several gases, and therefore is nottruly a perfect gas, it deviates under pressure somewhat from thecomposite effects of the Ideal Gas Laws. The deviation is called"Super compressibility". Super compressibility in not significantat the conditions at which most domestic customers are served;however, at the pressure at which pipeline gas and some commercialand industrial loads are measured, it is important that supercompressibility be included in the correction applied.
The subject of chart recorders will be covered first, followedby mechanical correction devices and associated peripheral items.Finally, the subject of load Survey equipment and its peripheralaccessories will be described.
- Product Code: AGA
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