LIQUID FLOWMETER CALIBRATION AND PROVING SYSTEMS                                                                         ABSTRACT Liquid flowmeter calibration and proving systems employ various basic techniques for establishing the performance characteristics of flowmeters. An overview, and evolution of the various applied technologies is presented. The three most common methods illustrated, and discussed are: •        Gravimetric •        Comparison •        Positive Displacement Industry definitions for flow calibrators versus flow provers, and primary versus secondary/tertiary methods are included. Transference of technology from the calibration lab to the field, and vice versa, has resulted in multi-use devices. Criterion for selecting the appropriate calibration/proving technology depends on the type, and intended use, of the flowmeter, and the environment under which the calibration/proving is conducted. The flowmeter manufacturers have an entirely different basis for selecting a technology, as opposed to end users such as an aerospace metrology lab, or a pipeline company involved in custody transfer transactions. Manufacturers of mature flowmeter types such as turbine, positive displacement, magnetic, and vortex meters, are constantly in the process of enhancing the features of their products. Such enhancements must be considered when evaluating the method with which they are to be calibrated or proven. Emerging flowmeter technologies such as coriolis, and multi- path ultrasonic meters, have imposed new and demanding considerations for existing methods of calibrating and proving flowmeters with “manufactured flow pulses”. Some of the most dramatic improvements in the last decade has occurred in the evolution of the positive displacement type of calibrators/provers. Comparisons are discussed between “conventional” sphere, and oscillating piston methods, and those for “ballistic”, or “small volume”, calibrators/provers”. A small volume calibrator/prover is basically defined as being capable of obtaining a precision of +/- 1 pulse out of 10,000 (0.01%), with < 10,000 flowmeter pulses accumulated during a calibration/proving procedure. Inclusion of ultra-precision, volume detector sensors, dual chronometry (pulse interpolation), and digital data acquisition, have contributed to a continuing evolution of these devices. Relatively new “hybrid” concepts are discussed, which address compatibility of existing calibrator/prover technologies with demands of enhanced flowmeter characteristics, and lowering the total cost of ownership. Issues relating to the intended application of a flowmeter should be considered when specifying the method of calibrating or proving that instrument. For example, a coriolis mass flowmeter is typically factory calibrated using a direct gravimetric calibration sytem, wherein the displaced calibration fluid is weighed. Alternatively, the device could be calibrated/recalibrated/proven, with a volumetric, positive displacement, calibrator/prover utilizing an “inferred mass” procedure. Such a procedure would include either the inclusion of a precision densitometer, or a weigh scale used to weigh the displaced volume of calibration fluid. A multitude of correction factors are employed with either of the above procedures, to present the calibration data at standard conditions. For a variety of reasons, the installed performance of a flowmeter can vary considerably from that stated on the factory calibration certificate. The stated “accuracy” of a given flowmeter can be no better than the precision of the method with which the device was last calibrated or proven.                                                          EDITED VERSION PUBLISHED IN AUGUST 2004, ISSUE OF                                                                                FLOW CONTROL MAGAZINE                                                        AS FEATURED ARTICLE: “ SET YOUR SIGHTS ON ACCURACY ”                                                   TO OBTAIN A COMPLETE COPY OF THIS ARTICLE – PLEASE INDICATE YOUR REQUEST                                            IN COMMENTS SECTION OF “CONTACT US” PAGE OF THIS WEBSITE