Modbus MFU Option Card Installation Manual
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Publication PUB091-004-00_0918
A multiple coil write by function code 15 to turn on more than one of the open, close, stop and ESD
coils in the same command is not permitted. If an attempt to energise more than one of these coils in
one command is made, an exception response is generated and the multiple write is ignored.
With the open and close coils, these will turn off once the actuator completes the command, a new
command is sent, the actuator is placed in local or some other interruption occurs. For example, the
close coil will de-energise once the actuator reaches the close position and stops. The stop and ESD
coils remain latched once turned on and are cleared by another command or writing 0 to the coil.
The ESD action works slightly differently in that even if the coil is reset to 0, the action remains latched
in the actuator. This is because a network ESD command overrides the actuator local controls. In
order to remove the ESD action it is necessary to write a new command and if the actuator has local
selected then the only command that will clear the latch is a write to the stop coil.
In the case of the DO-1 to DO-4 relays, they will follow the command, energising when turned on and
de-energising when turned off. These relays also maintain their status if the actuator power is
removed and reset to the de-energised state only when the power is restored.
5.1.3
Modbus Control using the ACTCON Register
A single register is provided to allow the digital control of the actuator. Writing a value to the register
with function code 06 or 16 causes the actuator to open, close, stop, ESD or partial stroke test and at
the same time cancels any other command set. This method of control removes the need to reset
commands written with a code 05 coil write with a second write to the same location. The number
written changes any coil states already set to the new value. Values of 5 to 255 cause no actions.
ACTCON Register (Register 5)
Value
Stop
Close
Open
ESD
Partial Stroke
0
✓
1
✓
2
✓
3
✓
4
✓
5.1.4
Modbus Control using the Actuator Position DV register
The analogue position control function will take priority over an earlier coil or ACTCON register
command to open, stop, close, ESD or partial stroke test the actuator when a value is written to the
Actuator Position DV register. The controller will then position the actuator to the desired value.
The analogue position control function is cancelled either by the actuator achieving the desired
position or a coil or ACTCON register write to one of the open, stop, close, ESD coils.
Note that when limited range positioning is used and the actuator is in the fully closed position a DV
value of 0%, or when the actuator is in the fully open position a DV value of 100%, are not acted upon.
5.1.5
The IQ3
‘S’ contacts (Modbus DOs).
The IQ3
actuator has four ‘S’ contact outputs that may be configured to report the status of the
actuator with signals such as Open Limit, Closed Limit etc. These are identified as S1 to S4.
