Securing NIST Calibration Traceability for Venturi Meters

This article describes the process that Primary Flow Signal, Inc. uses in order to secure NIST traceability on a venturi meter that is not laboratory flow calibrated.

Bench Calibration & NIST Traceability

By definition, bench calibration is the process whereby each newly manufactured venturi meter is analyzed, measured and thoroughly inspected to be certain that it meets the established design criteria including dimensions, tolerances, surface finish and pressure tap location and geometry that will support an accuracy guarantee of +/-0.5% of actual rate of flow over the applicable flow rate range fully traceable to NIST.

Steps to secure NIST traceability:

> The basic design geometry, tolerance and finish requirements for the HVT products are based on independent flow calibration in NIST traceable flow calibration facilities covering 39 different HVT meters ranging in line size from 2.0” to 48.0” in multiple calibration facilities. All meters calibrated were built according to the same manufacturing tolerance and finish requirements and all meters were built according to the HVT design.

On the attached “summary of calibration data” the results of 39 NIST traceable flow calibrations, as noted, is +/-0.41% of c. In this context, “c” is the discharge coefficient that has been determined to apply to the HVT metering geometry and the summary provides NIST traceable confirmation that in all cases, the deviation from the established discharge coefficient is +/-0.41% which results in compliance with the industry standard requirement of +/-0.5% for a non-wet flow calibrated venturi meter.

Because venturi meters have full hydraulic similitude characteristics, a 2.0” venturi meter will perform in the same manner as a 200.0” venturi meter as long as both meters are built to the same NIST traceable process.

> The measurement equipment that PFS utilizes in performing the internal dimensional and tolerance inspections as well as the surface finish and coating requirements are all fully traceable to NIST because we utilize outside calibration services whose test equipment is traceable to NIST. All measurement and test devices are independently calibrated at least once every 12 months and in some cases with greater frequency depending on their usage.

> Since our bench calibration of each venturi meter follows the same iso9001 certified process and is a documented work instruction for our inspection personnel, once all criteria are met, we assign the standard discharge coefficient to the new meter and certify its accuracy to be +/-0.5%.

PFS performs internal self-audits of our ISO9001 quality program throughout the course of every year which ensures that the step by step process which has been developed to support NIST traceable performance statements is maintained without exception.

Learn more about our calibration services, or contact PFS to connect with one of our experts.