Setting Up the MFU
Publication PUB091-003-00_0119
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11 TROUBLESHOOTING
In general, most of the problems that are seen with actuators fitted to a Modbus network are due to
wiring errors and are simple to test and fix.
Often, the problem is that the network is connected to the wrong actuator terminals. The correct
terminal numbers are given in the wiring diagram that comes with each new actuator. If this diagram
has been lost, then a new one can be found on the Rotork web site. The wiring diagram number is
usually given on the actuator name plate.
The terminal connections can be confirmed with a multimeter. With the actuator powered-down, a
resistance of approximately 270,000 ohms should be measured across the correct terminals. This will
also confirm that the actuator internal loom is correctly connected to a working MFU.
If the reading is open circuit, then there may be a loom problem (only to be seen in a retrofitted
actuator – all actuators are factory tested before shipping), there may not be an MFU fitted, or the
MFU may be damaged.
If the network is attached to the correct terminals and there are no communications, then perhaps the
A and B connections are reversed. These could be swapped, again with the actuator powered down,
and communications checked again with the actuator powered up.
If there are still issues with communications, then please confirm that the correct address, baud rate
and parity have been set in the actuator and that they correspond with the settings in the known
working DCS.
If there are still issues with communications, please contact Rotork Technical Support at the telephone
numbers given on the back page of this manual.
The following information helps with the investigation:
1. Actuator Serial number from the actuator name plate.
2. Wiring Diagram number from the actuator name plate.
3. Software version. If the actuator has a display, the software versions of the fitted PCBs may
be obtained by following the instructions in the actuator manual. If there is no software
version given for the MFU, then it may not be fitted. If the actuator has no display and no
communications, you will not be able to obtain the software version of the MFU.
4. Type of actuator.
5. Feedback from DCS.