Investigations on the force controlled piston gauge FPG8601 with non-rotating piston of nominal area 980 mm2 manufactured by DH Instruments Inc

Project Description

The aim of the project is

• to evaluate the equivalence of the pressure scales in the range 1 Pa to 15kPa disseminated by MIKES and PTB
• to compare force controlled piston gauges with different mechanical design in the range up to 7 kPa in absolute mode using a CDG as zero-indicator

Final Report 2004-03-15

New designs of measurement devices for measuring and realising small pressures are now available. They may be characterized in so far that they operate with a non-rotating piston, in contrary to the conventional piston-cylinder systems for realizing the pressure scale.

The pressure of those devices is defined by using a high precision load cell to measure the force exerted on the effective area of the piston-cylinder system. The piston is centered mechanically or by a constant gas flow through an annular gap. The measurement device under test (FPG8601) was one of the latter working method and was equipped with a precision pressure control unit and a software tool to be fully operated under PC control. Nevertheless such devices are secondary standards that have to be calibrated by conventional piston-cylinder systems of well known effective area or as in our investigations by a precision mercury manometer.

Before starting this project the force controlled piston gauge (FPG8601) was tested by MIKES in the gauge mode with the result that there was a difference between the effective area reported by the manufacturer and that determined by MIKES.

In the course of our cooperation the value of the effective area determined by MIKES could be confirmed with a small deviation of 5 ppm and finally there was a systematic difference of approximately 3.74E-5*p between the pressure values determined with the FPG8601 and with PTB’s precision mercury manometer. After a revision of the software package by the manufacturer the above mentioned systematic difference was nearly removed.

The results of the cooperation are summarized in the internal report: Comparison measurements between the Finnish Centre for Metrology and Accreditation and the Physikalisch-Technischen Bundesanstalt using a piston gauge of type FPG (force-balanced piston gauge of DH Instruments Inc.) in the range of small absolute and gauge pressures. Internal report PTB (2003); 3.23 ‘pressure section’, H. Ahrendt, Braunschweig, March 2003

In addition there will be available a MIKES Report (to be published).