Re: [foxboro] Analog input current about 2% low
- From: "Doucet, Terrence" <tdoucet@xxxxxxxxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Fri, 12 Jan 2007 08:10:20 -0500
The 4-20 mA drops through a precision resistor and the voltage produced =
there is fed to an analog to digital converter. This is vastly =
over-simplified but you get the picture. If there is some corrosion =
anywhere in the resistor or leads, you will see a higher voltage than =
the FBM was calibrated for and thus your +2% error. I'd replace the =
nose-cone.
Note that corrosion on the mA circuit should have no affect on your FBM =
reading as long as you do not saturate the supply voltage drop across =
the transmitter.
Terry
-----Message d'origine-----
De=A0: foxboro-bounce@xxxxxxxxxxxxx =
[mailto:foxboro-bounce@xxxxxxxxxxxxx] De la part de =
brad.s.wilson@xxxxxxxxxxxxxx
Envoy=E9=A0: January 12, 2007 6:25 AM
=C0=A0: foxboro@xxxxxxxxxxxxx
Objet=A0: [foxboro] Analog input current about 2% low
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=3D3 (4-20 mA) with KSCALE=3D1 and BSCALE=3D0. 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
=20
=20
_______________________________________________________________________
This mailing list is neither sponsored nor endorsed by Invensys Process
Systems (formerly The Foxboro Company). Use the info you obtain here at
your own risks. Read http://www.thecassandraproject.org/disclaimer.html
=20
foxboro mailing list: //www.freelists.org/list/foxboro
to subscribe: =
mailto:foxboro-request@xxxxxxxxxxxxx?subject=3Djoin
to unsubscribe: =
mailto:foxboro-request@xxxxxxxxxxxxx?subject=3Dleave
=20
_______________________________________________________________________
This mailing list is neither sponsored nor endorsed by Invensys Process
Systems (formerly The Foxboro Company). Use the info you obtain here at
your own risks. Read http://www.thecassandraproject.org/disclaimer.html
foxboro mailing list: //www.freelists.org/list/foxboro
to subscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=join
to unsubscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=leave
Other related posts:
