Powerflex 755 occasionally missing the speed reference

Why would I get "running at speed" on the him with a missed start? I zipped the program, but it's still to big to attach. I'll try to get out to it this morning to jog it and watch parameters.
 
The "running at speed" status does seem to conflict with the reference issue.

But I've seen dozens of instances of Stop/Start assertion conflict, and only a handful of inadvertent reference switches, which were always from digital or network "speed reference select" functions.

The fact that you are running indicator lamps with drive outputs also suggests that there is some digital I/O wiring. Be sure to tie all the unused digital inputs to DC common so they cannot inadvertently get switched high by noisy or floating wiring.

Try exporting the project as *.L5K and zipping that.

It really isn't productive to keep guessing or looking at partial screenshots.
 
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Thank you for posting the program !

The system has three PowerFlex 755's configured as CIP Motion axes (Shuttle, Tension, and CAT) and four PowerFlex 755's configured as ordinary variable speed drives (LETOFF_1, LETOFF_2, TAKEUP_1, and TAKEUP_2).

The drive that's not functioning as expected is Letoff_1.

All of the Tasks in the program are Periodic; there is no Continuous Task in the program.

The absence of a Continuous Task tingles my Spidey-sense; it's uncommon and there was a communications-related bug that mostly affected diagnostic I/O modules in some applications that have no Continuous Task. I would generally run the Main Task as Continuous instead of as a 2 millisecond Periodic Task.

The Reel Up features are executed in a 50 ms Periodic task, and the Letoff and Takeup drives all have 20 millisecond RPI values.

Calculated_Letoff_RPM is used by the Letoff_1 Program in the 50 ms periodic Reel_Ups Task, but it's actually calculated in the Math Program, which is executed after the Letoff_1 Program. So at least those calculations can't interrupt one another.

I was a little surprised to see the Letoff_1 drive configured with as many Output datalinks as it is. In particular, the Speed Reference A Setpoint is configured as an Output Datalink (Letoff_1:O.SpdRefAStpt).

As far as I can tell, that value is 0.0 and it's not linked to any logic. It should not matter because P545 is set to get the drive's speed reference from the network, not from a fixed setpoint.

So.. I'm not stumped, but I'm further along with my head-scratching.
 
If it were me I would take the start stop out of the function blocks and write it in ladder. I would then add contacts for the DRIVE_ACTIVE bit in your start and stop to leave the start high until DRIVE_ACTIVE is seen then transition the start low.

Same for the stop leave the stop high until the DRIVE_ACTIVE goes low.

Without this process I have seen countless powerflex drives hang up and do nothing when the start command is given. Programmers start scratching their heads because it is not repeatable, this stall if you will only occurs sometimes.

Also im not for sure but if a START command is given while the STOP is still high it will ignore it, even if the stop transitions low a few milliseconds later.

In other words, if START and STOP end up high at the same time and the stop transitions to low nothing will happen. For the start to be seen it has to transition back to low and then to high again, with the stop low, for the drive to start.
 
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Alternatively you could add to your function block if you so choose. The drive active bit needs to be in your logic for the stop command, unless im missing something it does not appear to be.

You also need to add to both function blocks to ensure interlocking for the start and stop commands to ensure they cannot be high at the same time.
 
I appreciate the help guys. Sorry for assuming your gender. I haven't had a chance to look at the wrapper today. It wasn't the closest alligator to the boat. I'll try those programming changes Dock suggested and let you know how it goes.
 
I would also do the Start/Stop logic in the same Ladder Logic diagram as the rest of the commands, if I had the choice. I just think more clearly in RLL than in FBD for discrete conditions.


Usually the symptom of a Start/Stop rising edge conflict is the amber "STS" lamp flashing, and a "Stop Asserted" message on the HIM module.

Parameter 2 really should show the reference speed. Unless there's somehow something selecting a zero preset, I don't know how it can be different from the Output command over the Ethernet.
 
Side note- it looks like whenever your drive faults the FBD logic automatically clears the faults? Are you sure that's what you want to have happen?
 
If it were me I would take the start stop out of the function blocks and write it in ladder. I would then add contacts for the DRIVE_ACTIVE bit in your start and stop to leave the start high until DRIVE_ACTIVE is seen then transition the start low.

Same for the stop leave the stop high until the DRIVE_ACTIVE goes low.

I agree that something needs to be done to prevent both bits being high at once but I've found that the above method causes an issue when using ramp stop mode if you decide to stop a drive and then quickly start it again. The drive will continue ramping down and not start up again until it has completely stopped. That's usually NOT an ideal response, especially if you have a long ramp down time.

My solution is to put an XIO "Drive.Stop" bit as a permissive for your "Drive.Start" OTE. That solves both issues and is simpler to boot, IMO.
 

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