This page contains a Flash digital edition of a book.
PROCESS EQUIPMENT UPDATE


Expert advice on flowmeters


Charles Wemyss lists 10 reasons why you should – and should not – calibrate your flowmeter


W


e use the word flowmeter to describe a device that measures the flow of a fluid. Mostly we’re considering gases or liquids in a closed pipe or conduit and we


need either the instantaneous flow rate or the total amount of fluid that has passed. There are many varieties of techniques dependent on the fluid being measured and


dependent on the flow rate, pressure, viscosity and more. The flowmeters range from miniature positive displacement devices to large electromagnetic or ultrasonic units used for pipes over 3m diameter. The way we garner confidence in the displayed value is through calibration. Most flowmeters are supplied by the manufacturer


with a ‘laboratory’ calibration. In other words, they have been tested in close to ideal conditions. Depending on the meter type, once installed in your process, that original calibration may be valid – or it may not be.


WHY SHOULD YOUR FLOWMETER BE CALIBRATED? There are a number of key reasons why it should be calibrated:


n To reflect the new, current conditions n Because some component has a wear factor n There is an accumulation of dirt or setting product, affecting the sensor.


n Because the calibration frequency states it has to be n Because the results don’t feel right compared to the rest of the process


n The process is producing poor quality product yet the flowmeter seems stable


The best calibration is that which is performed


in situ. Many of the variables are tuned out. The fluid is the same, as is the installation attitude, straight lengths, etc. That is the precise reason why engineers should re-calibrate; it gives them that confidence in the device. If in situ is not possible – for example, when the fluid is hazardous or at high pressure – then it has to be uninstalled and calibrated elsewhere.


Litre Meter’s latest rig is designed for calibrating ultra-low flowmeters


10 www.engineerlive.com


WHY SHOULDN’T IT BE CALIBRATED? Clean versus dirty is the first argument for not calibrating your flowmeter. If it comes out of the line dirty and is sent away for calibration then you would normally expect to ship it clean. The test laboratory calibrates it in the clean state.


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  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52