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Old March 5th, 2018, 11:16 AM   #1
TheWaterboy
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New build using AB PLC's and AB VFD's.

Building a new station (2 in fact) where I have the option to have AB VFDs .
These are 150 HP pumps so the VFD's are large and I want to monitor them well.
I believe there are AB VFD's (755?) that are intimately connected to the PLC using AOI's to monitor and control every aspect of them and there are the (725?) that are normal VFD with Ethernet comms and I assume CIP message control.

Prior to this I have had PowerFlex 4, 40, 70, 700 etc all controlled with 4-20ma so this comm ability of this quantity will be new to me. I have used CIP to talk to Altivar drives so I know that route is an ugly one.

What do I need to know to determine if I want to switch from 4-20 to Ethenet control? Better PID would be a great bonus as these can work under a pressure condition as well as a flow and level condition.

Are the motion series PLC's required for this? Its just VFD not multi axis motion. I'll be talking to the local reps soon enough and I'd rather sound like an idiot here than in that meeting.
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Old March 5th, 2018, 11:53 AM   #2
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Yes if you want the advanced features of the 755 you need a motion processor. For a small number of axis, I would use something like the 1769-L27ERM-QBFC1B. It gives you up to 4 motion axis, and some on-board IO.

Personally I love the new integrated motion, it makes the programming easy to swap between servo and induction motors.
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Old March 5th, 2018, 12:09 PM   #3
Ken Roach
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Quote:
Are the motion series PLC's required for this?
The PowerFlex 755 can be set up to act as a motion control axis, for which you would need a ControlLogix or a CompactLogix with the "M" CIP motion version.

But for the kind of pump control work you do, you definitely don't need those features.

I prefer digital connections because of the high resolution (no more worrying about 4-20 mA accuracy) and the amount of additional diagnostic and monitoring information I can get from the drives.
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Old March 5th, 2018, 12:35 PM   #4
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I can't imagine ANY need to use "motion control" on a pump!

The 755 and 753 are essentially the same VFD, but different formats. The 755 is intended for network control and has a built-in Ethernet port, but has NO I/O on board, you must add I/O by adding option cards, then it accepts up to 5 option boards (the "5" in end of 755). The 753 has no communications port on-board, but has basic I/O included, so is more apt for discrete control. If you WANT Ethernet control or any other network, then you add a comm card to one of the 3 available slots (the 3 in the end of 753), leaving you with two more slots available.

The 755 also has some enhanced control capabilities, such as the ability to run servo motors and PM AC motors, but all of that would be wasted on a pump application.

The PID control capabilities are exactly the same on both versions. You can have the VFD do the PID control, or since you have a PLC, do it there, that way if f a VFD must be replaced, the PID doesn't need to be set up again. The advantage to doing it in the VFD however is that if the PLC goes down and you have the VFDs wired for local control, the VFDs can still operate that way using their internal PID loop.

One reason then to possibly consider using Ethernet control then is that if you have a Control / Compact Logix PLC, you can implement what's called ADR, Automatic Device Replacement. You need a managed switch for your Ethernet, but what it can do for you is that if a VFD must be replaced, the person replacing it doesn't need to know how to spell VFD, they just hook up the 3 power wires in, 3 power wires out, plug in the RJ45 connector and cycle power. The managed switch sets the I/P address using Port Persistence, the Logix controller then can see the VFD and the Firmware Supervisor in it will flash the VFD's firmware if it's different from what the PLC is looking for. Then the PLC implements ADC (Auto-Device Configuration) to automatically re-load all of the programming into the drive from the SD card in the PLC. That makes it easier to go ahead and use the PID control that's in the VFD, because replacing it means nobody has to set it up again. If it's a remote pump station, this can be a really good thing to implement, because then ANY electrician can replace a VFD at 1:00 AM on a Saturday night (rather than calling you at the bar). You can implement this with either the 753 or the 755.
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Old March 5th, 2018, 12:42 PM   #5
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Ken, that is exactly what I was hoping for. But I'm not clear yet.
You are saying that I can use the same AOI's (which I assume exist for their VFD's) with a controller that doesn't have the motion version? and the "dumber" 755 is NOT an option I should look into in this case?
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Old March 5th, 2018, 02:10 PM   #6
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jraef
I was thinking that LOGIX instructions for VFD specific stuff was only on the motion version. I don't recall where I got that impression - probably from the help file.

The first pass has an L81E specified for the Controller, I can change anything I want but that seems ... robust enough

Thanks for that info - I will dig into it.
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Old March 5th, 2018, 03:25 PM   #7
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When you set up the drive in the Logix tree, in the drives dialog box in Logix you can set the speed reference to be controlled form the PLC and also set up the Datalinks to get what information you want for the drive and this will show up as a tag in the PLC.

To set this up right click on the drive in the tree and then click on the change button, and set up your drive size and what parameters you want to read back to the PLC.

Alan.
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Old March 5th, 2018, 03:39 PM   #8
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I've used Powerflex 525 and Powerflex 753 on ethernet many, many times. Never a 755, but the principle is the same.

Yes, you just need to install the AOP for the drive and then you can add it to your ethernet tree just the same as you would add a remote I/O rack. It works seamlesslessly and my OCD *loves* seeing just six power wires and an ethernet cable going to my drive.

There are a few tricks to getting it all working. You have to match firmware exactly, you have to match parameters, you have to set up datalinks, and so on. And then there's the "gotcha" with how to stage your start and stop signals so that the drive doesn't refuse to start. But once you've got your head around them, they're only little things and ultimately they all make sense as far as "why it has to be this way". If you want any more details on some of those "gotchas" just let me know.

As for an AOI - I don't know of one that is pre-existing for any of the motors. Maybe RA have developed one and posted it on the knowledge base somewhere - but I prefer to build my own regardless. I have one for the PF525 and all I have to do is point it to the I/O tags that are created when I add the drive to the ethernet tree, and it does all of the rest. Again, makes my OCD happy

I'd definitely be going for ethernet control. Pick the most cost effective drive for your application, build your AOI, and away you go.
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Old March 5th, 2018, 05:30 PM   #9
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Match Firmware... between the PLC and what exactly? Surely not the VFD!

interested in the gotchas, are these spelled out in the manual or hard won nuggets of wisdom?

I have a little 525 on the wall behind me. I guess its time to start poking at it.
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Old March 5th, 2018, 05:53 PM   #10
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When I say "match firmware", I don't mean the VFD and the PLC have to have the same revision - just that when you add the drive to the ethernet tree, you have to specify the revision, and it has to match the drive, or it won't communicate. You also have to specify the exact type. I'll attached a screenshot of a PF525 from a recent project to show you what I mean.

Generally the gotcha's are documented in the manual in some form or another, but as to how they relate to the actual real-world application (i.e. the exact manner in which the issue bites you), it's often not spelled out.

The start/stop one is well explained in this thread, especially Ken's posts #12 and #16 (this is Ken's second favourite topic, right behind controlling Powerflex Drives over Ethernet from an SLC).
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Old March 5th, 2018, 06:14 PM   #11
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OK I get that. Just like any module you install. Had me worried for a bit

Post #16 ... the last line seems to explain how elevator and crosswalk buttons work.

Thanks for that all. I'm gonna go lab this up
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