Multiple Mode Selections for VFD Drives

[tranh2 0]

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!

[JRoss 84]

I've never used ABB drives, but what you are trying to do is within the capability of at least the upper-level drives that I've used (AB PF700, Mitsubishi A700/F700). Many of the smaller drives also have multiple inputs, but often don't have the PID functionality, that would take some research. Just an idea - you might want to use a small HMI connected directly to the drive for things like PID setpoint and parameters. If they're something that would be adjusted frequently, using an HMI would allow you to customize the user interface to make those parameters easier to access, and it simplifies the analog wiring. That also might open up the range of drives that would meet your requirements, as you would only need two analog inputs instead of three.