Foundation Control Using Both Do And Ao Blocks - rotork Mk3 Technical Manual

If the AO output is set to 0% and limited range positioning is not being used (selected via the
Transducer block), the actuator will operate as though a 'close' command had been sent. Similarly, if
the AO output is set to 100% under these conditions, the actuator will interpret the instruction as an
'open' command.
Note that when limited range positioning is used and the actuator is in the range from fully closed to
the 0% position, an AO command of 0% will not be acted upon. Likewise, if the actuator is in the
range from fully open to the 100% position, an AO command of 100% will not be acted upon. See
section 6.2.4 for more information on limited range positioning.
5.1.4

Foundation control using both DO and AO blocks

With mixed position control using the AO and discrete (open/stop/close/ESD) control using the DO
blocks, the control settings must be carefully observed. Discrete actions will take priority over the
Position requests.
The single/multiple bit control option for the discrete controls has to be determined. When Boolean
Fan In is available, multiple bit control is set and a single DO block is used for the open/stop/close
discrete control actions. The DO block chosen must also include a condition to select Position Control.
With single bit control each discrete action requires a DO block to be enabled and the Position option
is in DO 4 which must be set to Mode 0.
When the AO value is to be adopted for the valve position, the control scheme must select the DO
block to be in its Position value. With multiple blocks DO 4 must be set to '1', all the others being '0'.
As soon as the discrete control changes to 'Position', the AO output value becomes the desired
actuator position and the position controller will move the valve.

DO control values of Open/Stop/Close/ESD have priority over the AO value.

The DO value must equal 'Position Control' for the AO value to become active.
The position controller will be subject to the considerations mentioned in 5.1.3 with regard to 0% and
100% values.
Publication PUB089-005-00_0618
Actuator Input Output Signals
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