controllogix bumpless transfer

Hello all,
I having trouble transferring from a manual control to automatic control. At the moment when the valve is in auto, it uses the PID loop to control it. When the vale is in manual it is controlled by changing the valve percentage from the HMI. I have tried to use a MOV instruction and take the manual percentage and place it into the pid out, when the vale is switched to auto. This works sometimes. Example if the valve is at 44% in manual and then I switch to auto the pid loop will hold it at 41% sometimes. Or the valve will be 44% in manual and then when switched to auto the valve will drop to 25% for no apparent reason. I'm not sure how to setup bumpless transfer on the PID. I have read that the .swm instruction in pid needs to be used. Any help would be appreciated. Unfortunately, I'm not a controls engineer so it may have to be dumbed down for me. Thx

Mavrick
to set the output of a PID control manually
First make sure the PID control is scanned and updated normally just like if it is in auto
then set the PID control to manual mode
then enter your manual set point in the PID output word
the PID control will update the internal values according to the manually set output
the when you set the PID control back into auto mode the PID control will have already completed the calculations and make the changed accordingly
if the PID control is left in auto mode it will try to correct for the manual set point you entered. the output will end up at full rail. Full output or 0 output and have to correct from there when you give control back

When you're in manual- set the .swm bit to put the PID into "software manual". Now you can write directly to the output and the PID will not calculate.

When you want to go back to automatic, just clear the .swm bit and stop writing to the output, and the PID will automatically do a bumpless transfer and start running.

so when in manual i would move the valve percentage into the .swm bit by using a mov instruction?

How do you set the pid to manual mode?

now let’s cover the “SOFTWARE MANUAL MODE” ...



again suppose that your PID tag is named “My_PID” ... to use the SOFTWARE MANUAL MODE, we use the built-in tagname “My_PID.SO” (instead of the “Tieback” tag) ... put a 1 into the BOOL at My_PID.SWM ... this step will put the PID into the “SOFTWARE MANUAL MODE” ... now enter a value into My_PID.SO ... for example: 31.0 ... the value from My_PID.SO (31.0) will be sent to the PID’s output ...

This something i found on the forum good information. Looks like I use a mov instruction to move a one into th pid.swm when placed in manual. Then place my valve percentage in the pid.so.
I'm assuming no tie back needed

Right, tie-back is not needed.

If you are using the "PID" instruction then bumpless transfer happens automatically.

See PDF

Also, be aware that when manipulating the .SWM bit and .SO register in your program logic, the effect of changes on the CV will not occur until the PID instruction is next scanned.

Thank you everyone for all your help. Tried it out this morning worked great!