Bilateral Comparison in the Calibration of Atmospheric Tank Provers by Volumetric and Gravimetric Methods

摘要

Calibration of liquid quantity meters may be carried out volumetrically by collecting a known volume of liquid in a standard vessel. In this volumetric method, the standard vessel often known as atmospheric tank prover takes the form of a container with a calibrated volume. In its turn, calibration of the tank prover volume can be carried out by weighing the water contained in the vessel, or carried out using smaller volumetric measures which are themselves traceable to national standards by weighing methods. This paper presents a bilateral interlaboratory comparison in the calibration service of atmospheric tank provers carried out by Institute for Technological Research of the State of Sao Paulo (IPT) and Weights and Measures Institute of the State of Sao Paulo (IPEM-SP). The main objectives of the comparison were to validate the calibration results of two accredited laboratories and to comply with the requirements established by the accreditation standards regarding the participation of calibration laboratories in proficiency tests. Another important objective was to evaluate the comparability of the calibration methods used by the laboratories. IPT used the gravimetric weighting method and IPEM-SP used the volumetric method. The performances of the laboratories in the calibrations were quite satisfactory for both atmospheric tank provers used in the comparison. The normalized errors obtained were between 0.08 and 0.15 for the 20 L tank prover and 0.05 to 0.22 for the 1 000 L tank prover, indicating a very satisfactory comparability between the two calibration methods.