Modbus MFU Option Card Installation Manual
30 of 76
Publication PUB091-003-00_0119
5.1.1
Controls Priority
Since there are three potential sources for control inputs the actuator and Modbus Module assign a
priority for those occasions when two or more commands are applied simultaneously.
In addition, for the IQ / IQT and SI / EH actuators, the remote control hard wired inputs can be used as
discrete input signals, to report the status of other devices or as control inputs. The associated
Auxiliary Input Mask parameter must be set for the IQ / IQT or SI / EH to select the required function.
In the case of the hard wired input for ESD this can be configured either as an ESD/DI-4 signal or as a
‘Modbus Command Inhibit’ to prevent network control signals from moving the actuator.
High Priority
Low Priority
Local Stop
Local Close
Hard Wired Close
Modbus Close
Local Open
Hard Wired Open
Modbus Open
Hard Wired ESD
Hard Wired Stop
Modbus Stop
Modbus ESD
Modbus Position
Mechanically interlocked to prevent both at the same time.
The IQ/IQT and SI/EH can be set so that Local Stop has a higher priority than ESD.
Only one Modbus command is possible at a time.
If a Modbus command is applied whilst Hard Wired Stop is present, stop is cancelled.
Fig 22:
IQ / IQT and SI / EH Controls Priorities
In the case of the Q actuator the control selection is slightly different because the actuator uses a
different control circuit. The Local Controls have a higher priority than hard wired or Modbus controls
and the hard wired and Modbus controls share the same priority level
If the Stop/Maintain hard wired input is closed (to provide maintained action on the other
contact inputs to the actuator) then position control via Modbus cannot be used.
The recommended connection is to use only an open and close buttons or contacts and
‘push to run’ mode where the actuator only moves whilst the contact is closed.
If a Modbus and hard wired input are both present the control priority is set by the actuator
priority setting
High Priority
Low Priority
Local Stop
Local Close
Hard Wired Close
Local Open
Hard Wired Open
Hard Wired ESD
Modbus Close
Hard Wired Stop/Maintain
Modbus ESD
Modbus Open
Modbus Position
Modbus Stop
Mechanically interlocked to prevent both at the same time.
The action depends on the Actuator Control Priority setting.
Only one Modbus command is possible at a time.
A Modbus Position command must not be applied whilst Hard Wired Maintain is present.
A Modbus Stop command is not possible if Hard Wired Maintain is present.
Fig 23:
Q Controls Priorities
