Powerflex 40p Won't restart after STO

wine_sparky

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May 2016
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If I give my PF 40p a STO signal, then attempt to restart after, it won't. No Faults.

I end up having to remove the start and FWD command, then re-apply them.
After doing that, the drive will run.

Any thoughts?
 
That sounds like correct operation to me. It's been a while since I've used anything in the PF40 family but most drives will not acknowledge a start command if the drive is not ready to start when the start command goes active.

Keith
 
I think the Schneider VFDs will show nST in this situation too. I always remember it as “no start”, I think it’s actually freewheel stop command. Usually it’s from the run command given when the drives not ready. You must remove the run signal before the drive will run again.
 
Welcome to the PLCTalk forum community !

That sounds like both proper operation for a Safety-related circuit and normal operation for an A-B drive.

A safety circuit typically cannot allow automatic restart of a machine after an emergency stop, just because the emergency stop has been reset.

And A-B drives have always required a rising-edge of the Start command (while the Enable is on, and the Stop is not asserted) to start the drive. That's been normal since the days of the Bulletin 1336.
 
we had PF525, every time if STO circuit is open (we use it for E-STOP), the drive is faulted, after we release E-STOP,we try to clear fault, there are two ways to clear fault: one is from PF525:O.ClearFaults, another is pushing STOP button on HIM,but both ways would not clear this fault. what we do is that we turn off and turn on the circuit breaker which supplys 3~AC 480V to the PF525 drive, that will reset this fault,after that we can start the drive with no issue.
 
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Sounds correct to me as well.

It would be just like a manual motor control. If the control power kicks out, any and all seal circuits drop and you have to re-start them.

This is much the same. I wouldn't expect it to just start up if the STO came back on.
 
Hi and also Welcome to the Forum!

wine_sparky said:
If I give my PF 40p a STO signal, then attempt to restart after, it won't. No Faults.

I end up having to remove the start and FWD command, then re-apply them.
After doing that, the drive will run.

Any thoughts?

For a minimum Category 3 / Performance Level d (Cat3/PLd) Safety function, as well as tripping the STO you must also disable the drive (remove Enable) and assert a Stop (includes removing the Start).

Note: On the PowerFlex 40P (and PowerFlex 70 Class) drives, the STO option module has only one Safety channel input. However, the Enable input is a solid state input which acts as a second Safety channel input.

The Safety relay (or controller) when tripped will open its output circuits which should then remove power from both the STO and Enable inputs. This provides a level of redundancy in disabling the drive.

Atop that, the Safety relay (or controller) output circuits should also remove power to the Stop/Start inputs, asserting a Stop to the drive. As the power for a Stop, Start and a FWD input circuit, etc., are typically all from the same source, this should mean that the Safety function will simultaneously remove the power from all these control inputs.

The STO module on your drive also provides an auxiliary "Monitor Contact" which you should wire to the Safety function's monitored reset circuit, if required.

Only after the Safety relay (or controller) has been reset, and the STO and Enable inputs are restored, should a valid Start/FWD command be issued to the drive. Depending on where these commands are issued from (hard wiring or controller, etc.), you must ensure the above is implemented.

On the topic of automatically restarting these drives in general, there is indeed also a standard auto reset/restart feature on these drives. We may set certain parameters to allow an automatic reset/restart after a Type 1 Fault (Example: Motor Overload). This is just to inform in general that it should not be thought of as "not ever permitted" to automatically restart these drives.

What should determine whether this feature would be allowed or not is a Risk Assessment (dirty words again). Certain machines, operations or processes may indeed be perfectly safe in having a function restart automatically, if assessed as such. But as Ken mentions, "typically" for Safety functions, on relatively dangerous equipment, this tends not to be permitted.

For more information, clarification, and verification on the above, please reference the following manual for your DriveGuard Safe Torque Off Option...

https://literature.rockwellautomation.com/idc/groups/literature/documents/um/pflex-um003_-en-p.pdf

Note: Page 17 tables the status of the STO/Enable channels, along with the auxiliary status signals made available in the drive.

Regards,
George
 
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Hi,

Thanks for the input. Just to be clear. I over simplified my original post. I am most definitely removing the start command during the sto.

I’d did find the problem though. The Start command was being applied too soon in the reset process. The reset (which requires several presses) not only resets the pilz safety PLC, but also the logic in the AB PLC. Because of the way the multi-step process works, the AB PLC logic was resetting before the Pilz. The STO , which is reset via the Pilz, was resetting after the Run Signal.

I simply added a “Drive Ready” bit in front of the run command.
Problem solved.

BTW. The stop and start signals are not hardwired, they are Eth/IP

The weird part of this whole thing is that it is an OEM piece of equipment, this problem only started now, after about 3 years of working fine...strange.
 
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The weird part of this whole thing is that it is an OEM piece of equipment, this problem only started now, after about 3 years of working fine...strange.
I've seen something similar before when I upgraded the safety systems on a machine and replaced a standard safety relay with a Pilz Multi Mini safety PLC. The servo drive kept giving us a fault. When I eventually tracked it down, it was to do with the timing of the safety input, which had previously been wired to a relay output on the safety relay, but was now wired to a solid state output on the multi mini. Turns out that the handful of milliseconds it takes for a mechanical relay to switch was long enough for the servo to do whatever it needed to do before seeing the safety input come on, but once it was on a solid state output it was more or less instantaneous, and the way the PLC logic was written, there was no way out of this situation. Had to make a small logic change to the PLC to make it work again. I just couldn't believe that the code was written in such a way that relied on the mechanical operation time of a relay to function correctly.

So, in your situation, maybe a component has been recently changed for a newer model that acts ever so slightly differently?
 
wine_sparky said:
...The Start command was being applied too soon in the reset process...the AB PLC logic was resetting before the Pilz. The STO , which is reset via the Pilz, was resetting after the Run Signal...

Say what?...

You sound like you are saying that the reset button (I assume?) resets the Safety function and then resets logic which attempts to restart this "piece of equipment"?

If so, that is not permitted. You may have a manual or an automatic reset of the Safety function, but you may not have an automatic restart upon reset.

IEC 60204-1 / EN 60204 Safety of machinery – Electrical equipment of machines – Part 1: General requirements

This Standard dictates that...

There must be no automatic restart of the machine on reset

With there appearing to have been no preconditional interlock between the Safety function being reset and the controller Start command, and the above, if true, it would suggest there are possibly several aspects of this OEM "piece of equipment" which were not implemented correctly?

Very worrying.

Regards,
George
 
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Say what?...

You sound like you are saying that the reset button (I assume?) resets the Safety function and then resets logic which attempts to restart this "piece of equipment"?

If so, that is not permitted. You may have a manual or an automatic reset of the Safety function, but you may not have an automatic restart upon reset.

IEC 60204-1 / EN 60204 Safety of machinery – Electrical equipment of machines – Part 1: General requirements

This Standard dictates that...

There must be no automatic restart of the machine on reset

With there appearing to have been no preconditional interlock between the Safety function being reset and the controller Start command, and the above, if true, it would suggest there are possibly several aspects of this OEM "piece of equipment" which were not implemented correctly?

Very worrying.

Regards,
George

You are correct. It is the way the OEM equipment was shipped.
 
we had PF525, every time if STO circuit is open (we use it for E-STOP), the drive is faulted, after we release E-STOP,we try to clear fault, there are two ways to clear fault: one is from PF525:O.ClearFaults, another is pushing STOP button on HIM,but both ways would not clear this fault. what we do is that we turn off and turn on the circuit breaker which supplys 3~AC 480V to the PF525 drive, that will reset this fault,after that we can start the drive with no issue.

You can tell it to have a no fault if STO is open, t105.
 

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