[foxboro] Analog input current about 2% low
- From: brad.s.wilson@xxxxxxxxxxxxxx
- To: foxboro@xxxxxxxxxxxxx
- Date: Fri, 12 Jan 2007 05:24:44 -0600
We have a perplexing problem. One 4-20 mA input on a FBM04 is reading
consistently lower in the AIN block than at the transmitter. The AIN is
set for SCI=3 (4-20 mA) with KSCALE=1 and BSCALE=0. We've bench-tested the
transmitter (Rosemount 3051) and it is right on the money, both with the
HART and independently measuring the current output. What I see in the AIN
is that both the RAW counts and the MEAS values are showing 0.8 psi lower
than the transmitter (this is about 2% of scale). The odd thing is that
this is across the range, so it looks like a bias. We've replaced the FBM
and the problem is still there. We're going after the nosecone next.
Could there be a drain in the wiring, like a poor termination, that would
show a constant reduction in current? Anybody seen anything like this
before?
Brad Wilson
Process Control Engineer
ExxonMobil Chemical Co
Edison Synthetics Plant
732-321-6115
732-321-6177 fax
Brad.S.Wilson@xxxxxxxxxxxxxx
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