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Calibration facilities extended to meet customer demand

February 2004 News

Seven state-of-the-art calibration rigs costing more than £500 000 have been installed at Krohne's Coriolis mass flowmeter worldwide manufacturing and service facility in Wellingborough, UK, to meet the growing customer demand for the revolutionary Optimass range.

The new Optimass range of Coriolis mass flowmeters provides class-leading accuracy, repeatability and ease of installation, as well as offering a whole host of innovative new features and benefits for the user. The single straight tube design is the first of its kind with wetted parts in titanium, stainless steel and Hastelloy C-22, for outstanding corrosion resistance, while the Optimass z-tube meter is designed specifically for low flow.

Krohne's investment in the new rigs reflects the company's commitment to maintaining its reputation as a leading supplier of mass flowmeters calibrated to the highest standards. Every Optimass meter undergoes a stringent six-hour calibration test to guarantee that it will perform according to the high standards of accuracy laid down by Krohne. At the end of each complete cycle, a calibration certificate is printed for the customer to act as an ISO 9001 quality document.

The market-leading performance of the Optimass Coriolis mass flowmeter range is due to the incorporation of Krohne's AST (adaptive sensor technology) design. The meter's precision performance depends on precise calibration. Each meter must be calibrated to a mass flow accuracy of 0,1% of measured value and a density accuracy of 0,2% of measured value, over a wide range of operating temperatures.

Product manager, Stephen Ratcliffe comments, "The superior mechanical design and construction of our rigs and the use of high quality control valves that guarantee leak tight shut-off, ensures our calibration process is as exacting as possible. To maintain the integrity of the calibration data, the operation of the rigs is entirely computer controlled; at each stage, the Optimass meter under test communicates to the control computer using its on-board RS485 data link. Any uncertainties in the testing system have been reduced to an absolute minimum. This is vital if the derived calibration factors are to be unaffected by external influences, and thus directly attributable to the flowmeter itself."

Because the primary function of a Coriolis meter is the direct measurement of mass flow, all seven calibration rigs operate using the mass balance system, pumping water through the meter into a weigh scale over a period of time. The total value of flow measured by the flowmeter is compared to the actual mass measured by the weigh scale, and a meter calibration factor is calculated accordingly.

All seven Krohne weigh scales are regularly calibrated by Mettler Toledo to an accuracy of 1 in 20 000, using weights that are traceable to National Standards. Mettler Toledo is authorised by the United Kingdom Accreditation Service, the ultimate authority for the mass measurement standard in the UK.

The density measurement of the flowmeter is calibrated on the basis that the density of water at any temperature is a known physical variable. By measuring the exact temperature of the water in the rig and calculating its theoretical density, Krohne can compare this to the actual density measured by the mass flowmeter, and calculate the appropriate calibration factor.

To ensure calibration for the widest range of potential variables in customer applications, Krohne uses water at three temperatures; 20, 40 and 60°C for all mass flow and density calibrations. Other fluids that are less dense than water, such as diesel oil - or more dense, such as barium chloride solution, are used to meet specific customer requirements.

For more information contact Gordon Duff, Krohne, 011 315 2685.



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