A novel calibration of the Large Piston Prover at INRIM

INRIM realizes its flow rate standard using three distinct facilities, aimed at measuring different flow rate ranges; in particular, for the larger flow range (10-2600 L/min) a piston of 1000 mm nominal diameter and 1200 mm nominal stroke is used. The traceability of the standard is obtained through dimensional calibration of the piston, regarding both the piston size and its stroke. The first calibration of the machine was performed at its initial installation. Even if most of the relevant documentation about this first calibration is not available, INRIM realized a procedure similar to the old one and performed measurements to renovate the first facility calibration. The present paper will dedicate special attention to the description of the measurement chain used for the calibration of the piston in its own siege. Moreover, the method for the transfer of traceability from the length standard to the measurement of the piston diameter will be discussed; it should be noted that the dimensional study is not completed yet, because the first set of measurements described in the present work, evidenced the criticalities of the procedure adopted in the past. For this aim, a further measurement campaign will be carried out in order to minimize the uncertainty associated to the dimensional measurement of the piston and of its displacement. Finally, the results of first dimensional evaluation will be presented alongside.