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Naphtha Tank Level Variation w.r.t Day and Night
Naphtha Tank Level Variation w.r.t Day & Night


Diaphragm seal capillary DP type measurement envisaged for Naphtha drain oil tank measurement. But, the tank level varies automatically based on day and night. We are not having any temperature and pressure measurement at naphtha drain oil tank.

Kindly suggest how to resolve the level variation.
My email id:

are all feed and drain valves closed?

You may need to check any sight glasses, or possibly "stick" the tank...

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A capillary seal pressure measurement is, by definition, a closed, filled system which is as much a thermometer, reflecting temperature changes, as it is a pressure measuring system. Capillary seal DP level measurements are inherently subject to error due to temperature variation. Even if you had temperature measurements, you'd have to engineer the correction table yourself.

I know of one guy who tried to insulate and electrically heat trace the capillaries and the seal to a slightly elevated, but stable temperature and he managed to get the level deviation on a static, unchanging level down to 6mm, but it was a project (temp sensor location on the capillaries was a problem, I seem to recall he ended up with 7 zones, 2 for each capillary and 1 for each flange/seal, 1 for the process heads on the DP xmtr) and he said next time he'd change level technologies.

Alternative level technologies are
- the ERA system Emerson makes that separately measures the high and low pressures with an electronic connection between the pressure sensors, not mechanical, filled capillary.

- any number of vendors' radar, guided wave or contactless.

Thanks David,

Presently, we do not have any temperature measurement on Naphtha tank. Now, we are trying to take ambient temperature measurement and configure the density correction of Naphtha based on Ambient temperature. Whether this will resolve the level variation or we have to measure tank temperature.

The variation is observed in day/night signifies that it is a ambient temperature related issue. You may cross check the DP transmitter's reading with local level gauge if you have one.