Some considerations on handling the calibration results of capacitance membrane gauges

Capacitance diaphragm gauges (CDG) are widely used also as transfer instruments; consequently, they need to be referred frequently to primary systems mostly in the (1000 – 0,1) Pa range where no other accurate gauges are available. They must be characterized individually since a general rule on their metrological behaviour is not possible. Various CDGs are calibrated at IMGC for the Italian Accreditation Service. The aim of the present paper is to demonstrate that, for each gauge and after the first calibrations, it is possible to arrive at an equation which represents the calibration coefficient as a function of pressure and is based on a reduced number of experimental points; as a consequence the time for a complete calibration procedure is cat down. One of the four gauges we examined, for which many calibration curves were available, was considered for a complete evaluation; then the evaluation model was applied to other gauges.