GE RX3i PID Bumpless Transfer

Hi,

I am trying to implement bump less transfer from manual mode to automatic mode of built in GE PID block (I'm using PID_IND), but not sure what to do.

While searching I found:

With a GE or Siemens PLC my program turns on the Manual bit of the PID loop. When manual is on the manual setpoint is moved into the PID loop. When manual is switched off the PID loop takes off from there - naturally bumpless. Then when in Auto (not manual), the program moves the pid output to the Manual setpoint, making it bumpless the other way.

Click to expand...

I'm not sure what is meant by "the manual setpoint is moved into the PID loop".

How I understand you must overwrite one of the registers of the PID memory, but none seem to have this functionality.

Can anyone shed some light on this for me? Any more info you need let me know.

I've been using the "CPU Reference Manual GFK-2222M" to get info about the PID block (CH 10).

I can't say off hand that this is a problem for you but GFK-2222'M' is an old Manual as 'T' is now available: http://support.ge-ip.com/support/index?page=docchannel&id=S:DO186&actp=search

In general moving "Data" around in the PLC is a rather simple and BASIC maneuver. Use "MOV_INT" or MOV_WORD" depending on the Data type. Remember that PID loops do not use DINT or REAL Data Types in these PLC/PAC's.

The PID Function Block uses (IIRC) 40 16bit INT Type Registers.

Thanks for that manual, it actually describes how to do it!

From the manual:

In order to assure a bump-less transfer from Manual back to Automatic mode, the user program should copy the PV to the SP before switching back to Automatic mode. This allows the algorithm to update the last sample period time and prepare to re-calculate CV based upon the new Auto Mode SP commanded.

Click to expand...

Unfortunately I don't have a GE PLC to test on, so I want to get it correct before I put in live PLC.

From what I understand to handle the bumpless transfer from manual to automatic:
- On first scan of changing to automatic (just before PID is solved), copy PV to SP
- On subsequent scans use Operator entered SP

Is my thinking correct, or do I need to PID solve once while in manual mode with PV copied to SP?