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Old February 19th, 2018, 09:37 AM   #1
Slate744
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Fancy Exclamation Powerflex 525 StepLogic PLC Control

Hello everybody. I am a new poster to this forum, but have been using PLC.net to help me through issues for a long time now. So I have to say thanks to all the contributors!! So back to my question.

I have 2 powerflex 525 drives connected by ethernet to a compactlogix PLC. I want to use steplogic to slow down and speed up a motor using a trigger bit. My "running" speed is operator controlled by HMI. What I want to achieve is normal running speed until my trigger is made then slow down/dwell the speed for a set time(Which will change based on my run speed), then back to normal run speed again, then repeat. Is there a module defined data type that I can write to, to set my speed reference and step timer?
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Old February 19th, 2018, 10:38 AM   #2
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Why would you want to write logic in drives that are controlled by a PLC? It seems to me that it would be much easier to simply write this logic in the PLC program.
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Old February 19th, 2018, 11:41 AM   #3
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As above, the 525 is probably one of the easiest drives to get talking and spinning with a compact logix, get that to do all the thinking. Much easier to implement and the next guy will thank you also.
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Old February 19th, 2018, 12:35 PM   #4
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Agreed. In order to implement in within the drive, you would need to change the command/control point from being the Ethernet port to being the VFD. That itself makes it more complicated than just doing it all in the PLC.
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Old February 20th, 2018, 12:31 PM   #5
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I am worried about damaging the drive switching speeds ever .5 sec or more. If i disable writing to eeprom will that prevent the damage I am concerned about? My thinking was using the step logic built into the drive would prevent damage.
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Old February 20th, 2018, 12:41 PM   #6
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I can still control the drive by Ethernet with step logic feature. Iím just unsure what tags to write for freq reference and time for each step.
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Old February 20th, 2018, 01:52 PM   #7
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If you have EDS & Module files for the drive installed I believe it should be easy.
Your drive should have an Input / Output datatype in your controller tags.

Find that tag (whatever you names your drive in the ethernet device tree).
Look at the Drive:O tag and expand that
The last part of that datatype should be FreqCommand its an INT

This is Frequency * 100 so 6000 is 60Hz
Write to this with the speed you want it to run to.

You can also look at the :I tag and check the feedback for what speed it is actually running at, or just look at Drive:I.AtReference.

Then do your timer then change your FreqCommand.
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Old February 20th, 2018, 08:24 PM   #8
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Quote:
Originally Posted by Slate744 View Post
I am worried about damaging the drive switching speeds ever .5 sec or more. If i disable writing to eeprom will that prevent the damage I am concerned about? My thinking was using the step logic built into the drive would prevent damage.
Perhaps you should consider hiring a professional to assist you with this project.
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Old February 20th, 2018, 08:44 PM   #9
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What these people are saying about how easy the 525 is to integrate into the logic is true....I can't think of any downside to doing it that way.

The speed control is as simple as writing to a tag.....that's it.

Do you already have the drive added to your project and do you see the tags we're talking about?
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Old February 21st, 2018, 10:14 PM   #10
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While I agree with the posts above I think that the OP’s answer got lost somewhere along the way. It sounds as if you want to trigger a % reduction in speed from a set point then return to that set point. Having dug into the step logic functionality in the past, I don’t think this is possible.

The StepLogic can trigger a series of stops/starts, direction, and speed changes based off of time or digital inputs. It’s not terribly difficult to set up, but can be for a novice. Another issue is that it is difficult to troubleshoot when it is not operating correctly. You also cannot set proportional changes to my recollection. You will be dependent on changing the speed references or switching between preset speeds. I suppose you could have proportional speed control if you got creative with the input wiring, but at that point you really should get a PLC to control it. If the Compactlogix is too expensive then pick up a micro 800. The compactlogix have gotten so affordable though that it would be silly not to choose it.
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Old February 21st, 2018, 10:24 PM   #11
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Quote:
Originally Posted by Slate744 View Post
I am worried about damaging the drive switching speeds ever .5 sec or more. If i disable writing to eeprom will that prevent the damage I am concerned about? My thinking was using the step logic built into the drive would prevent damage.
It's not going to damage the DRIVE to do this, and I'm not sure what you mean by the eeprom issue. Writing to the drive command word has nothing to do with the eeprom as far as I know.

Changing speeds ever 1/2 second is unlikely to be implemented in your motor however; basic laws of inertia will likely prevent that from having any real effect on the load speed.
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