Drum Level Fluctuation Due to Rain


Thread Starter


3 DP type drum level transmitters are installed at our site. Whenever we experience rain at our location, the raw value of these transmitters changes causing wide fluctuation in drum levels. As the raw value from these transmitters changes due to rain, control valve responds and results in wide variations in drum level.

Kindly respond if anybody else has faced such situation and what was the solution adopted.

Thanks in advance.
Is it possible that the sensing lines are cooling (or changing temperature) due to the rain? That would cause an error...
Without further information, there are three typical causes of fluctuating signals during a rain storm. The first and fairly common is that the rain is cooling off the level transmitter connections (impulse lines), the level bridle, and/or cooling the process where the process level is actually fluctuating (level sight glasses may be able to determine this). The second is that water is getting into your wiring or transmitters somewhere (fairly unlikely with three transmitters). You might look at what the level transmitters share in common as a clue (e.g. a common cause failure) as to what can affect them all. The third is that sometimes lightning accompany a rain storm or there is a ground shift due to moving charges in the rain clouds affect ground charges. The first can introduce noise into your system and the second, a ground shift can also cause noise sometimes if you are not grounded properly.

Is this a new thing, i.e. have these loops worked before in rain? If so, what has changed in the level loops?

Are all the level transmitter's response the same? If so or not, that may be a clue.

William (Bill) L. Mostia, Jr. PE
ISA Life Fellow,
Winner of the 2018 ISA Raymond D. Molloy Award
Sr. Functional Safety Consultant
SIS-SILverstone, LLC.

"No trees were killed to send this message, but a large number of electrons were terribly inconvenienced." Neil deGrasse Tyson

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