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Title: Investigation Of Temperature Influences On Gas Meters
Author: Rainer Kramer, Bodo Mickan, Fritz Mgerle, Roland Schmidt
Source: 2009 International Symposium on Fluid Flow Measurement
Year Published: 2009
Abstract: As basically known for each kind of measuring instrument, the measurement deviation of gas meters depends from a list of influence values. In the last 2 decades input perturbations as well as the gas pressure (which leads to different gas densities and hence Re - numbers) were major subjects of interest. The gas temperature have to be investigated as an important influence figure because the application of gas meters may differ much from the calibration temperature. The impact of the temperature depends from the technique used for the flow or volume measurement in the meter. The investigation of temperature effects on gas meters is needed increasingly for type testing of meters used for custody transfer, the estimation of temperature influences on the measurement uncertainties especially if used as flow standard and the evaluation of performance figures claimed by the manufacturers. The European regulations on Measuring Instruments (MID) require the investigation of all influences and hence of the gas and the environment temperature on the behavior of gas meter as part of the conformity assessment. PTB as a notified body for MID assessments wants to carry out the metrological key tests itself, other tests will be accepted, if they are done by accredited test laboratories for instance. In order to follow this policy PTB developed and realised a test rig for temperature tests in a range between -45 C up to 80 C. The main features of the test facility as well as the chosen technical solutions will be described in the paper. The facility was designed to investigate all kind of gas meters as well as flow standards like critical nozzles up to a flow rate of 300 m3/h at standard conditions. The rig is able to stabilise the temperature in a test chamber in which the MUT is installed as well as the temperature of the test gas separately. For this the test gas flows through a heat exchanger which is equipped with an own it temperature control system. In order to avoid ice creation especially in the heat exchanger, the test gas is dried down to a dew point of - 60 C. The design uses preferably critical nozzles as flow standards which are installed under ambient condition in the test hall. By this approach a total uncertainty of U 0,2 % (k2) is reached for the flow rate at the conditions of the MUT (Q 0,1 m3/h, -25 C up to 60 C). First results of the investigation of laminar flow elements, wet gas meters (drum type) and mass flow elements based on a thermal principle are described. The results show considerable influences, which may be eliminated by appropriate correction approaches.

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