Hello All,

I was hoping to get some input and ideas from some experts in here.

What we are trying to do is to have three control modes for a VFD controlled pump (ABB-ACF600), described below:

1. Local Mode - Selected/controlled through operator interface - No further info needed.

2. Local/PIT control Mode - Drive does all the controlling to meet a pressure controlled setpoint. There is no PLC interaction at all. A PIT signal shall be hardwired to the drive for process feedback. Another analog device capable of sending an analog signal shall be hardwired to the drive for process reference (Setpoint).

3. Remote/PLC Mode - The PLC will send the process control signal to the drive. This signal shall be a 4-20mA signal to the drive through hardwired I/O.

We were hoping to have a selector switch of some sort to select between the Local/PIT mode and Remote/PLC mode. Local mode will be selected through the drive local operator interface. Where we are getting caught up is how the drive will select the process reference (setpoint) source (PLC or Analog setpoint Device).

Would we wire PLC reference setpoint to AI1, PIT variable to AI2, Analog Setpoint to AI3? When we select EXT1 we would use AI1 (PLC control) and ignore AI2/AI3.

When we select EXT2 would it use AI2 as the process variable & AI3 as the process setpoint and VFD and be able to control through the drive PI controller?

Is the above not feasible with this drive?

Is there any device out there that is capable of being fed two different 4-20mA signals and having one output depending on what you select on the interface? Preferably, we don't want to do anything funky with switches.

If you have something better ideas I'm also open to that.

Thanks all!

 

Not familiar with the ACF-600, but you pretty much have it right I think. Following is based on ACS-550 and 800, the two drives (of any brand) that I'm most familiar with.

For PIT mode, set the EXT reference to PID1OUT and the PID1SP to the setpoint AI (all the PID stuff is in group 40, I think). You can set the setpoint source to KEYPAD rather than the third AI, which I think is what most people do. Use one of your DI's for EXT1/2 select.

But...I never do PID direct in the drive unless the customer designs the system that way. There's just so much more you can do in logic in the PLC, that I put in a PLC even if controlling the PID is all it has to do (but you'll always find a few more things to do with it once it's there). I mean to the point that even if you're sending down a remote pressure setpoint from a large PLC or DCS (the mode you're calling local/PIT), put a little $200 PLC locally just to be your loop controller. In fact, with a DI from your remote system to the local loop controller PLC, you could indicate whether the analog is a speed or a pressure setpoint, and set your AO to the drive accordingly.

 

Hi tranhs2,

I have no experience with ABB Drive,but this case will be easily implemented on Allen-Bradley PowerFlex 755/700S drive. Logic program like your requirements can be implemented using DriveLogix or Devicelogix whic is available for Powerflex 700S / 755.

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/20d-um002_-en-p.pdf

Thanks and regards
Ikhtiander

 

Hello,

This may be the stupid answer.

What about using one aux. contactor with 2NO + 2Nc and picked when we want the control from PLC.