CALIBRATION FEATURE CUTTING CALIBRATON COSTS – THE BENEFITS OF GOING MOBILE
weeks or longer, potentially causing a costly process shutdown. Flow service centres may provide premium testing and calibration services that are faster, typically taking between 48 and 96 hours, and even a 24-hour emergency turnaround service – but, the quicker the service, the more costly it becomes. An alternative is to have the testing and
calibration performed on-site. Some automation technology vendors provide mobile flow calibration units, which can visit sites to perform the service. Emerson, for example, has several of these units in operation around the world, and has now expanded its service to cover the United Kingdom and the Republic of Ireland. When a mobile unit visits a facility,
Jonathan Page, at Emerson, explains the advantages of having a mobile flow calibration unit visit a facility, rather than shipping flow meters to a flow service centre for calibration
T
here are several reasons why it is vital to have confidence that flow meters
are performing reliably and to their required level of accuracy. These include achieving consistent product quality, reducing waste and rework, providing a safe working environment, and ensuring that the correct amount of material is delivered, especially in fiscal measurement applications such as custody transfer. Before flow meters leave the factory to
be installed for the first time, they are calibrated to ensure they will achieve accurate and reliable measurement results. However, over time their accuracy will inevitably begin to drift, a gradual deterioration that can be caused by a range of different factors, including the effects of corrosive or erosive fluids, dirty processes causing build-up, and the aging of the device’s electronics. To return a flow meter to its original
level of accuracy, it is necessary to recalibrate the device periodically. The time interval between calibrations typically depends on the requirements of the relevant industry standards and regulatory body, and the confidence levels demanded by users. When used in fiscal measurement applications where absolute accuracy is critical, such as in the oil and gas or spirits industries, flow meters are usually required to be calibrated at least once a year. However, a flow meter used in an application where accuracy is non- critical can often operate for several years without needing to be calibrated. Calibration typically involves a flow
meter being taken out of the line and shipped to a flow service centre operated
/ PROCESS&CONTROL
by an automation technology vendor and accredited to the international ISO/IEC 17025 standard covering the competence of testing and calibration laboratories. The meter is tested by comparing its accuracy against a known reference – such as a weigh scale or master meter – in controlled conditions, and it is then calibrated using adjustments to match the reference. The required accuracy of the master meter varies according to different standards, but it is generally accepted that the reference should be at least three times more accurate than the device under test. For example, a Coriolis flow meter claiming 0.1% mass flow accuracy would need to be tested and calibrated against a reference with at least 0.03% mass flow uncertainty. When a meter is calibrated at a flow
service centre, the uncertainty can be as low as 0.014% of the mass flow rate, providing the best possible assurance that the meter under test is performing to its original specifications. However, shipping meters for testing and calibration can result in devices being off-site for two
When a mobile unit visits a facility, typically four to six meters per day will be tested and calibrated by experienced certified engineers
usually four to six meters per day will be tested and calibrated by experienced certified engineers. Typically, this includes testing a meter’s electronics to verify that it works correctly, plus checking several calibration points against a Coriolis reference meter, and adjusting the meter under test as required, to match the reference. Flow meters up to 3” in diameter can be tested and calibrated and these can be Coriolis, turbine, magnetic or vortex devices from any vendor. It should be noted that the reference
uncertainty percentage achieved at a mobile unit is not quite as low as at a flow service centre, so devices should not be calibrated at a mobile unit if they are being used in fiscal measurement applications. In addition, mobile units typically use water as a calibration medium, but regulators demand that meters used for fiscal measurement are calibrated in an environment that replicates the real application as closely as possible. For example, the Oil & Gas Authority in the UK insists that oil must be used as the calibration medium, and that testing must take place at a temperature and pressure consistent with the real environment in which the meter operates. However, for applications other than
Mobile flow calibration units such as this can visit sites on pre- arranged dates
fiscal measurement, the reference uncertainty that can be achieved at a mobile unit is still low enough to satisfy regulatory requirements. The Coriolis reference meters used in Emerson mobile units have an industry-leading uncertainty of 0.08% of the mass flow rate, and calibration documentation is provided. Furthermore, mobile units provide other benefits, such as a faster, more convenient and less costly service, while returning a device to the line more quickly minimises process downtime, thereby increasing throughput and profitability.
Emerson
www.emerson.com
PROCESS & CONTROL | OCTOBER 2020 21
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44
