Specifications

SQ: 1-43
RS3: Service Quick Reference Guide
Troubleshooting
Multiplex I/O Troubleshooting
Condition
Action
Multiplex input
point(s) bad.
1. Put an appropriate substitute signal
into the point. Verify the accuracy
to determine if the problem is
system or field related.
CAUTION
Always remove field DC power
before working on a 4 -- 20 mA
input Front End Module (FEM).
NOTE: FEMs should not be
removed or i nserted with power on.
If the problem is in the system:
a. For thermocouples, check the
configuration of the MIB. Verify
that the “SIG CHAR” field is not
configured for millivolts
(example: J NBS is correct ; do
not use NBS mV).
b. For 4--20 mA inputs with the 10
ohm dropping resistors
mounted on the marshaling
panel, remove the field wiring
and measure the resistance of
the resistor.
c. Replace the FEM.
2. Remove the i nput signal from the
FEM. Configure the MIB for “Raw
Counts”. The MIB input reading
should be about 20000. If it is
much lower, replace the FEM.
MIB I/O Block configuration s hows FEM
type
“None Type C”.
The FEM may have been inserted with
MUX power ON. Turn MUX power OFF
and then ON to force the MUX CPU to
reinitialize.