A REVIEW OF GAS-OPERATED PISTON GAUGES

While hydraulic piston gauge technology dates from the mid-1800s, the first practical gas-lubricated pneumatic piston gauges for metrologica l applications were not developed until almost one hundred years later . The major reason for this delay was the need for adequate materials and machining technology to fabricate pistons and cylinders with tight enough tolerances for acceptable instrument operation. As the need fo r reduced uncertainties increased for gas pressure measurements in the ranges covered by manometry and above, technological improvement in g as-operated piston gauges advanced rapidly. Requirements for the devel opment of high-quality air bearings added stimulus to the push for imp roved piston and cylinder technology. Investigations into the possible use of pneumatic piston gauges as primary pressure standards competit ive with manometry had begun by 1965. Although lack of a fundamental d etailed model of the vertical momentum transfer from the moving gas to the flanks of the piston currently somewhat limits this application, improvements in understanding and technology are continually being mad e. The relatively recent discoveries of the sometimes significant depe ndence of the effective area of certain pneumatic piston gauges on the gas species used during operation, or on whether the gauge is operati ng in the gauge or absolute mode, underscore the need for continued re search in this field.