Re: [foxboro] FBM 211 min. HW-Rev. 0J

Dirk,

The PSS for the FBM211 states:

"Each channel performs A/D signal conversion using a multiplexed =
Sigma-Delta converter."

So the A/D is shared and given your statement, that 8 lockup at one, =
then there are likely 2 converters per card.


"The channels are not galvanically isolated from each other, but are =
galvanically isolated from ground and module logic.  ......."

So it is up to the user to ensure the the signal commons for all =
(perhaps in groups of 8) channels maintain near zero volts between =
channels - at all times!  This is almost impossible to ensure unless =
great care is taken in the design of the field wiring.  Most users find =
that such care is impossible to maintain and therefore specify complete =
isolation between channels and individual A/D converters per channel.  =
The FBM201 meets such specifications. =20

Many of the DCS manufacturers do not offer group isolated IO modules but =
some do offer group isolation. Many PLC manufacturers also offer group =
isolation so it is up to the user or his consultant to ensure isolation =
in the field circuits.

If marshalling racks were used, the task becomes even harder to maintain =
for 100% of time the FBM211 is in use.

You should check the complete schematic of your field wiring to see if =
you can find field powered transmitters where the common might be =
grounded or where the wires pass near high voltage wires or wires for =
solenoids or relays that can cause a voltage spike.  Maybe you can find =
two or three bad loops that you can move to an FBM201.  If thermocouple =
converters were used on any inputs, check for isolation at the =
converter, if not isolated, can you swap for an isolated version or move =
this signal to an FBM01?  Most TC's are grounded so you need to get =
isolation into the loop somewhere.

If your entire facility was mesh grounded per IEC 61000-5-2 you might be =
able to operate with group isolated IO converters like the FBM211.

Terry




Objet=A0: [foxboro] FBM 211 min. HW-Rev. 0J

Hi List.
=20
Since more than one year we had problems with the 16-Analog Channel
FBM211.
Sometime the first or last 8 Values bumps up. And all Values seems ok.
=20
We had checked several thinks.
Know we had the Information that the min. HV-Rev. of FBM211 is "0J"
This is said in SI 0-00560 from October 2005.
=20
To prevent of problems, please check your FBM211 HW-Rev.
=20
Regards
 Dirk
=20
 
 
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