Magnetrol Displacer Level Transmitters - serious problems!


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We are having persistent problems with 10 out of 16 magnetrol displacer level transmitters which we have installed in Nov 2001. They are all model E6 (EZ series), installed on 7 separate vessels. Quite a few are installed in 'pairs' with one being for shutdown and one for control.

The problems are mainly with flat-lining and or significant deviation from the other transmitter, but both these problems can be corrected (for a short-time at leas) by isolating/draining/ refilling the displacer chamber.

It is unlikely to be earthing problems causing this. The displacer chambers (which were locally made - not magnetrol cages) do have sufficient clearance for the displacers. Hydrates are also not a problem at the temperatures/pressures involved. Wax or build-up is something we plan to investigate.

The service varies but problem transmitters all involve measurement of hydrocarbon condensate, either liquid/liquid interface or liquid vapour interface.

Does anyone have any suggestions on what the problem here could be or has anyone had similar experiences?
Hello DM
I don’t recognize the part number to identify the product. No problem as there is so many types available. The displacer type has 1 or more floats that switch an application – on or off. You mentioned a transmitter, which makes me think it’s something else.

Just to be sure - is your problem with the flag type displacer that has a float running inside a tube – or another model?

Thanks Bob Hogg

Peter Baker Partners Instrumentation Inc

Encountered similar situation with natural gas filters at a large pipeline company. Magnetrols were measuring knockout oils. Kept sticking in stiling well due to oil residual build up.

Peter Baker

Thanks for your reply.

They are all LVDT (Linear Variable Differential Transformer) type. As the displacer moves up and down with the changing interface level, the steel stem moves relative to the primary and secondary windings (in the transmitter head) changing the induced currents. Output is 4-20mA.

The displacers are all installed in chambers external to the vessel (so vessel disturbances shouldn't be the problem).

It is difficult to say at this point whether the problem is mechanical (friction, blockages etc.) or whether it relates to the transmitters and installation (intrinsically safe loops etc.)

Any ideas?
What fluid/substance are you measuring, i.e. what is in the vessels ? Could be build up on the rod where it goes through the seal rather than in the displacer chamber itself. When you vent/drain the chamber it may be enough to "knock off" the residue round the rod when it moves suddenly.