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A repeatability test is conducted during the calibration to ensure meter confidence.

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The error limits are defined for each meter series and type as defined by the manufacturer. A tolerance band of acceptable error is shown on the calibration sheet within which all test points must fall.

The calibration data sheet can typically certify a minimum of two, up to 10 measurement points against a gravimetric standard.

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serial number, model number, and test person and date) are noted. The test points, measurement uncertainty determined, and identification of the meter (i.e. A hardcopy calibration data sheet is produced for each meter. Q: What are the options for flow calibration of my flowmeters made by a traceable calibration laboratory?Ī: Most flowmeters undergo a traceable flow calibration prior to shipment to ensure accuracy and repeatability. Dots define the calibration points on the calibration data sheet on a graph, which must fall within the boundary lines that indicate allowable error. For a calibration to be successfully completed, the documented points must all fall within the published accuracy specification of the flowmeter. Q: How do I interpret the accuracy of the calibration performed at various points documented on the calibration data sheet?Ī: The difference between the target (the value measured by devices in the calibration laboratory) and the measurement (the value from the flowmeter being calibrated) divided by the flowrate used for a specific calibration point equals the error as a percentage of the actual flowrate. Generally, the meter is calibrated with flowrates of 5 percent and 20 percent of their full-scale capabilities since linearity increases with an increase in flowrate, thus reducing customer costs by reducing high calibration flowrates and the associated manufacturing costs.

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Tests on thousands of flowmeters have shown that to meet the published accuracy, a series of tests are run at low and partial full-scale values to ensure they will meet their uncertainty tolerance when operated at full scale.

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A statement of flow meter total uncertainty usually includes: percentage of rate plus a percentage of full scale. Q: Why was my meter not tested at the full-scale flowrate?Ī: Meter uncertainty (total error) is greater in low flow ranges for all flow technologies. For example, Coriolis mass flowmeters are only calibrated in mass flow units. Stipulations do exist, however, and the manufacturer should be consulted prior to specification of custom calibration. As more points are chosen, the cost required to perform custom calibrations becomes more expensive. In fact, special calibration points and ranges are often specified on meters for critical applications. This does not mean a custom calibration could not be performed at unique points like low flow ranges. Q: What options exist in calibration related to flowmeters?Ī: Flow calibrations are performed at flowrates typical for the meter size and based on standard measurement points defined from a history of like meter calibrations. These factors include, but are not limited to, the accuracy or repeatability of the comparative standard used, calibration interval of the master standard, comparison procedure, unit conversion error, failure to perform field adjustments at reference conditions, failure to consider all error factors, or actual test meter drift or error outside of manufacturing tolerances.Ĭonsequently, the best recommendation is to consult with the manufacturer and ask for help or a re-certification at the calibration facility. Q: How do you know if the measured value is correct?Ī: The confidence of measured value agreement resides with the original manufacturing laboratory, the range of uncertainty of the technology being used, and the manufacturer''s practices and accreditations.įield proving activities can be used as a point of reference, but may be influenced by a number of factors.

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