IMO Precision Controls i3 Tutorial page 9

Next we have to enter the logic to control the fan for the reading of the temperature
controller. If the Present Value is greater than the Set Point then we need the fan to
switch on.
Select the Greater than icon from the Compare functions menu and insert it in a rung
with a N/O contact assigned to "always on". Set up the function so that the inputs are
PV and SP. Have the output of the function driving a bit, %M1 named "Auto_Fan".
Lastly we need to insert the logic for the manual override. The user will be able to
switch on the fan even when the temperature doesn't demand it. To do this we are
going to "OR" the Auto_fan bit with a Man_Fan bit that then operates the Drive_Fan
bit, that is communicated to the VXM drive.
Insert a N/O contact and assign to %M1. using the Vertical line tool draw two
lines and the beginning and end of the previous contact. Insert a N/O contact in the
gap just created and assign to %M2. Connect this OR gate to a N/O coil and allocate
to %M3.
That is all the ladder logic required, thanks to the protocol config option.
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