Rory,
The input resistors in FBM01 and FBM04 modules is only 50 ohms, and the
hand-held configurators that we have (Rosemount HART and Foxboro FoxComm)
require at least 250 ohms of loop resistance for the modulated signal to
work properly.
We routinely add a 200 ohm resistor in SERIES with the transmitter at the
terminal strips that connect to the FBM's on loops that have smart
transmitters, so we can communicate via HHT's.
-Brian Bates.
"Loupe, Rory (RJ)" <[EMAIL PROTECTED]>@lists.TheCassandraProject.org on
08/30/2001 11:52:08 AM
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Subject: FBM1, HART 275 and Rosemont 3051 Transmitter
Our instrument guys are having trouble communicating with a HART 275
communicator to a Rosemont 3051 level transmitter while connected to the
Foxboro I/A FBM1 input point. The instrument is being loop powered by the
FBM1 (P and P+). The only way we can get it to communicate is to put a 250
ohm resistor across the pair of wires (parallel). This allows us to
communicate with the transmitter but we will not want to do this will the
instrument is in service. I have tried this with several different HART
275s, FBM1s and 3051 level transmitters. If we disconnect the loop from
I/A
and use an Altec to power the loop, everything works as it should. This
eliminates our cabling as a problem, in my humble opinion.
Has anyone else experienced this problem? Is there a solution to allow the
communicator to work without a resistor across the pair of wires?
Rory Loupe
The Dow Chemical Company
LHC-3
P.O. Box 150, Building 6801 21255
highway 1,
Building 6801
Plaquemine, LA 70765-0150 USA Plaquemine,
LA 70764 USA
Phone: 225.353-6409 Fax: 225.353.6968
E-mail: [EMAIL PROTECTED]
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