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Drum Level Span
Drum level span not as drum level transmitter

First post in this forum, however I do follow this board.

I would like to understand a discrepancy that I found:
Control system ABB infi90
HRSG drum pressure is 310 PSIG
Drum taps 22" on one unit 24" on the other unit
both DCS and transmitter span are the same
DCS drum level transmitter span -8 to +16 = 24"
transmitter drum level span -21.5" to -3.5" =18"

I do understand that the total span for the transmitter is 18" of water. What I do not understand is why back in 1992 the engineer decided to span the drum level at the console to -8+16 = 24" span.

Both will be at zero level at 9.33 MA and usually the transmitter for a drum is set to tap distance or sometimes, like in this case, to a lower value. But usually the DCS and transmitter total span do match (taking into account for density change).

Does this forum know why the span of the transmitter does not match the span at the DCS? anything that I am overlooking?

By farhanmazari on 27 August, 2019 - 12:56 am

Interesting, I think generally we set two ranges in Infi90 system. One at AIS block another at AOL block.

Please check both values.

The liquid density is a function of temperature, and the detailed dimensions of the instrument connection.