# VFDs and Light Curtains



## billymac93 (Apr 4, 2015)

We have a VFD driven (AB525) turntable directly controlled by a light curtain's safety circuit. If an operator even momentarily trips or resets the safety circuit, my drive switches. The motor driven by the VFD has a solenoid driven disk brake for stopping asap. The drive is continually faulting -F111 Hardware Safety - and the brake is darned near wore out after six months. This is an OEM unit , not something built in-house.
Question: Is this arrangement of VFD and safety circuit "normal". I thought it better to have a safety-rated contactor downstream of the VFD and have it controlled by the safety circuit. I have contacted AB with my questions via e-mail but do not expect a quick response. I hope my learned brethren may share their experiences/knowledge on this design.

Thanks


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## micromind (Aug 11, 2007)

I don't know offhand if the 525 has this ability or not but I've had pretty good luck getting rid of the brake and using DC injection for a quick stop. 

This way, the VFD controls everything within itself; no outside stuff to interface with.


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## Flyingsod (Jul 11, 2013)

No no no.. don't just stick a device that will open the motor feeders while the motor is running via a VFD. Lotsa bad things can happen including killing your drive.

Now there is a way this can be fine... If you program or engineer into the control circuit a rung that turns the drive off before the contacts open. Of course then what is the point of opening the feeders?

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## sparkiez (Aug 1, 2015)

The 525 has a "Safe Torque Off" option.

http://literature.rockwellautomation.com/idc/groups/literature/documents/at/safety-at140_-en-p.pdf

It is perfectly reasonable to use the light curtain to activate the safe torque off on the drive provided that the light curtain is rated to "switch" the contacts on the drive.

I don't know specific wiring, but from what you have said the light curtain breaks the safety circuit, which then needs to be reset. The drive will not reset, meaning that the safety circuit is still open.

Start with the voltage feeding one side of the light curtain. Check for your 24VDC and follow that all the way through the curtain and verify that you are getting voltage back to the terminal. Even with the drive faulted and the system down you should be able to trace the voltage through. This should point you to your problem.

If you ARE getting voltage back through to the drive, you need to check connections on the terminals, at the splices etc to make sure that this isn't the cause of the issue.

If all connections are solid and making good contact and you can read voltage all the way back through your light curtain and the drive still won't reset, perform the same procedure through the reset circuit. If that fails, chances are you have a bad input on the drive.

Good luck!


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## Flyingsod (Jul 11, 2013)

I just looked up that fault, the drives output has exceeded it's current limit. Is there any way you can check the controls to make sure that the drives output is turned off BEFORE that solenoid brake system gets activated? Be sure the drive is getting a command to turn the output off and not just a regular stop command which might include a delay and or ramp down period. GL

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## sparkiez (Aug 1, 2015)

Flyingsod said:


> I just looked up that fault, the drives output has exceeded it's current limit. Is there any way you can check the controls to make sure that the drives output is turned off BEFORE that solenoid brake system gets activated? Be sure the drive is getting a command to turn the output off and not just a regular stop command which might include a delay and or ramp down period. GL
> 
> Sent from my C6725 using Tapatalk


Here is the excerpt from the manual:

F111 Safety Hardware 2 Safety input enable hardware malfunction. One of the safety inputs is
not enabled.
• Check safety input signals. If not using safety, verify and tighten
jumper for I/O terminals S1, S2 and S+. • Replace control module if fault cannot be cleared.

Fault list found here:
http://literature.rockwellautomation.com/idc/groups/literature/documents/du/520-du001_-en-e.pdf


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## Flyingsod (Jul 11, 2013)

Google failed me? :'( Thanks for the correction

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