PF 755 Stop Asserted

VulcPAC

Member
Join Date
Oct 2018
Location
Mallorca
Posts
21
Hi:

I am controlling a PF 755 via ControlNet, dpi port. When I send a stop command through the command word (bit stop in 1), the VDF receives the command (I can see Stop Asserted status) but it continues in "Running" status and the motor is still rotating. What can cause that the VDF continues active but whith a stop asserted status?

Thanks
 
I have never heard of a PowerFlex drive failing to obey a STOP command.

STOP commands always override all other drive commands, and have done so for every A-B drive I have worked with for almost three decades. To my knowledge, STOP commands cannot be masked or disabled from any SCANPort or DPI adapter on any A-B drive.

Does this happen every time your logic attempts to stop the VFD ?

Are there other ways to successfully stop the drive, other than Emergency Stop ?

How long does the condition persist ? Is the VFD configured for "coast to stop", or "Ramp to Stop" ? What is the Decel Time ?

Where do you see the "Stop Asserted" indication ?

Are you 100% certain that you are monitoring the correct VFD and motor ?

Are you 100% certain that the STOP command bit is staying on constantly ?

Again, this is a very unusual condition to report, so I want to be sure that you very carefully check your evidence and assumptions.
 
Hi Ken: Firast, thanks for your answer.

I will try to quote your questions...

I have never heard of a PowerFlex drive failing to obey a STOP command.

STOP commands always override all other drive commands, and have done so for every A-B drive I have worked with for almost three decades. To my knowledge, STOP commands cannot be masked or disabled from any SCANPort or DPI adapter on any A-B drive.

Same to me, first time thast I see this very rare issue. In all networks that I have worked, stop bit from command word override any other commands.

Does this happen every time your logic attempts to stop the VFD ?

Yes, every time. Then I have to go to MCC and stop via Enable input

Are there other ways to successfully stop the drive, other than Emergency Stop ?

No, just Emergency Stop and ControlNet

How long does the condition persist ? Is the VFD configured for "coast to stop", or "Ramp to Stop" ? What is the Decel Time ?

Coast to Stop, but I am not 100% sure, I am not in plant now

Where do you see the "Stop Asserted" indication ?

In the blinking led, the HIM and the status in Drive Executive

Are you 100% certain that you are monitoring the correct VFD and motor ?

Yes, because of what I have explained before, that I shut down Enable bit and the VDF with motor stops

Are you 100% certain that the STOP command bit is staying on constantly ?

Yes, I mantain latched the stop command until running status is off. So, as the running status remains in 1, I never unlatch the stop command

Again, this is a very unusual condition to report, so I want to be sure that you very carefully check your evidence and assumptions.

I have another machine with the same logic and the same VDF and don't have that problem. So, mi hope was that an specific "hidden magic" parameter, owner or mask is bothering, but as now, cheking most common configuration, both VDF have the same programming.

Thanks
 
check the stop method on the vfd
if it is set to ramp to stop the run output will stay on while the vfd ramps down to stop
if it's set to coast it should turn off with the stop command
the run output typically is on to show the vfd is controlling the motor
 
It's be a while since I really dug into one of these, much less with ControlNet. This does sound like very odd behaviour though.


Is there a "Stop Mask" in the PF755 that would all rejecting stop from ControlNet? Do you need to enable VFD start/stop control from the ControlNet interface?


What's the decel ramp time set at? Any chance it's ramping down very slowly? Disabling the drive might be doing a fast stop - ?



I'm reaching here so my apologies if these sound far-fetched.
 
I've seen it happening several times when cheap, high 'slip' motors have been used or replaced originals.

The solution was turning Slip Compensation off (P621=0; it is defaulted to 60 rpm) or using a lower slip motor.

Refer to RA Knowledgebase Answer ID 520932.
 

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