New apparatus for calibrations in the range of 2 kPa absolute pressure

Abstract

Capacitance diaphragm gauges (CDGs) are precise electromechanical pressure sensors in which the displacement of a stretched thin metal diaphragm is detected by the measurement of a capacitance. These are very accurate gauges, and are frequently used as transfer gauges. To calibrate such accurate low-pressure gauges, precise mercury manometers have been used. However, complexity, concern about mercury vapour, and cost of mercury manometers have made it difficult to use these manometers in many industrial calibration laboratories. As a substitute, gas-operated piston gauges can be used for the calibration of such low-pressure gauges. However, the minimum pressure that is necessary to balance the tare weight, which generally corresponds to a pressure of several kilopascals, is a major obstacle. To reduce this minimum operating pressure, we adopted a variable bell-jar pressure method. To realize this method effectively, we developed a new mass-handling device that makes it possible to add or remove weights up to 200 g easily, with a resolution of 10 g, without breaking the vacuum during the calibration. This calibration system can be used to measure pressures from 100 Pa to 2 kPa in the absolute mode. In this paper, we also present the calibration results for two types of CDGs with full-scale ranges of 1330 Pa and 1000 Pa, respectively.

Performance aspects of gas-operated pressure balances as pressure standards

“…Conventional pressure balances can be used as standards for absolute pressure below the limit of their normal operating range determined by the mass of the piston and load table. One way of achieving this [3,17] is to establish p r as the desired absolute pressure (see figure 1). For best accuracy, two pressure balances are used in a similar manner to the differential pressure standard discussed above, with the desired low pressure p r established above one pressure balance and balanced by a small mass added on the other pressure balance.…”

A low differential pressure standard in the range of 1 Pa to 31 kPa at KRISS

“…The basic design and principle of operations are described in other papers [4][5][6]. In this paper added and upgraded functions are described in detail.…”

Temperature inhomogeneity in the MSL primary pressure standard during operation

“…Because the unique environment and apparatus around which each piston-cylinder is used in different laboratories affects its temperature differently, there is no standard approach to assigning an associated uncertainty that is common to all realisations. Estimates of the size of the temperature variation across a piston-cylinder unit can vary by an order of magnitude between different realisations [1][2][3]. We have assumed, for our setup, a maximum possible temperature gradient of 0.20 K which corresponds to a standard uncertainty in generated pressure of around 1.8 ppm.…”