PD Gas Meters

The flow rate in household units is 0-7 scmh (0-250 scfh), and that of industrial units is up to 4,000 scmh (100,000 scfh). The errors of the standard designs of these sensors are 0.5-1% FS over a rangeability of 200 1, and their high-precision designs are available at 0.5% AF over a 100 1 range. 

PD gas meters measure volumetric flow by internally passing isolated volumes of gas in a process of successively filling and emptying compartments. This filling and emptying process is controlled by valves and is translated into rotary motion to operate a calibrated register or index that indicates the total volume of gas passed through the meter. 

The liquid-sealed drum meter is the oldest commercial PD gas meter, which is no longer used in industry because of difficulties such as changes in liquid level and freezing. These limitations were overcome by the development of the two-diaphragm and the sliding vane meters. Their principle of operation, however, has remained the same for almost 150 years. 

The diaphragm meter consists of four chambers. Differential pressure across the diaphragms extends one diaphragm and contracts the other, alter- 

Post- Oil Energy Technology After the Age of Fossil Fuels 

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Dirt and moisture are the worst enemies of the performance of all PD gas meters, so inlet filtering should be used when indicated. Pressure and temperature should either be controlled or compensated. The testing (or proving, as it is called in the gas utility industry) of gas meters is usually done by an accurately calibrated "bell" of cylindrical shape that is sealed in a tank by a suitable liquid. The lowering of the bell discharges a known volume of air through the meter under test. Other standards used to calibrate gas meters are calibrated orifices and critical flow nozzles. These devices compare rates of flow rather than fixed volumes. 

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