Hot:13672013-11-21 12:27:27 From: FTD Automation Instruments
Installation tips for Electromagnetic Flowmeters
we have emphasised the need to follow manufacturers’ instructions when designing pipeline installations containing electromagnetic flow meters. That said, the reliable operation and accuracy of readings depends on a number of critical details. This post gives not only further information on design factors but also some tips when actually installing inline Electromagnetic Flowmeters.
The first point to note, and one that is often overlooked, is not to install magflow meters in the proximity of strong magnetic fields as this will interfere with its operation. Such generators of magnetic fields are transformers, electric motors or HV or high current circuits. These are normally found in most processing plants and so consideration at the design stage is vital.
Next is the need to avoid air or gas bubbles in the liquid to be measured by the magflow meter. The first response to this is to note that these meters need to run full. This sometimes becomes a problem in low head conditions such as gravity systems or near an air valve on a pumped pipeline. Therefore, the plant or pipeline design should facilitate the positive ‘drowning’ of the meter position in say an inverse siphon or an upward slope of no more than about 3 degrees from the horizontal.
The second response to this bubble issue is to ensure that the sensor electrodes of the electromagnetic flowmeter are in a horizontal plane to avoid any air bubbles or gas coming out of solution would affect the readings the least. This is likely to be an issue with liquids in an operating pressure and temperature such that it is close to the phase change from liquid to vapour. In these circumstances, change to another type of meter or changing the process to avoid this situation is preferable.
Earthing of the pipeline and the magflow unit is an important issue to avoid stray induced magnetic influences. This is especially important for lined pipelines used for corrosive or clean fluids. For the most part, standard flange gaskets are useable. In some circumstances on lined pipelines, the magflow meter is to be fitted without gaskets. If specified an earth strap should be used across the flange or union.