Question about the Powerflex 525 and hybrid Eth/IP control

wine_sparky

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Join Date
May 2016
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B.C.
Posts
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Hi,

I'm looking to see if there is a solution for an application I'm attempting.

I have a PF525 running a pump. It is primarily hard-wired control and uses a 4-20ma signal as a speed reference. However, it is also connected to Eth/
IP and setup in a Logix 5000 project. I would like to occasionally control the speed via Eth/IP from my Logix project based on certain situations.

I know how to send the speed reference, but what I'm not sure how to do is to override it's local 4-20ma signal with the ETH/IP signal. I don't want to have to add any additional hard wiring to the VFD.

Does anybody know how to do this?
 
I don't have it in front of me but I'm pretty sure this is possible.



Set up Speed Reference 1 as analog input (it probably already is), and Speed Reference 2 as Ethernet/IP. Then you just need a signal to switch between speed reference 1 and speed reference 2. I *think* that it's possible to select the speed reference over Ethernet/IP - check out the data structure and see if you can see any likely looking tags to set.

Failing that, you could do something quick and dirty and creative:
1. Set speed reference 1 to Ethernet/IP and set the drive to use speed reference 1 at all times
2. Set up a datalink on the PF525 to read the value of the analog input back into the PLC
3. When you want the speed controlled by the analog input, have the PLC read the analog input and send it back out to the drive over Ethernet/IP as a speed reference
4. When you want the speed controlled by the PLC, just send your desired reference out
This would of course mean that it is no longer capable of running without the PLC, as the PLC acts as a signal relay. If that's not OK, there's another even dirtier and more creative workaround you could try (that would involve some very minor wiring at the drive, but only locally at the drive terminals):

Set up the system as described in my initial suggestion, but instead of using ethernet/IP to change the speed reference source, set it to a spare digital input on the drive. Then, wire a spare digital output from the drive to that input. Finally, set up a datalink in the PLC to control the digital outputs on the PF525, and have the PLC turn that output on when it wants to take over control.

Hopefully one of those solutions works for you!
 
Thanks for those suggestions.

I don't think #1 will work (unless somebody can correct me) because I don't think that it is possible to set the speed ref selection via ETH/IP datalinks (maybe with explicit messaging)

#2 is definitely not desirable in this instance.

#3 Will work for me. But I'd like to hear more feedback on #1
 

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