Display Flickering on PowerFlex 40

tvll

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Join Date
Feb 2020
Location
West Coast
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1
(Noob here)

I have a machine with a series of PowerFlex 40s.

When the machine is idled and no motors are moving, or being told to move, the frequency displays should be reading 0.

One VFD, that drives a motor for a system that we are having a problem is flickering between 0 and some number I can't really read .3 or 3.

I was wondering if this indicates a problem with the drive? Should the display be rock solid 0 or 0.0 when not being commanded, or is this normal? There are about 5 other drives, all which are rock solid at 0 or 0.0 (not at work so can't see)

We are having a little problem with the "system" that VFD drives and aren't sure if the VFD is causing a problem, or if it something else.

(Searched this forum and Google for flickering PowerFlex display and got no results, so I tried to do some homework before asking here.)

Thanks for any help.
 
Welcome to the forum!

What controls the speed of these drives? If it's an analog signal, it's possible that there's a small amount of noise on your cable. A lot of PLC programs will write a zero to the speed command if the drive isn't being told to run, but there's no reason you have to do that - you could still have a stopped drive sitting there displaying a 50.0Hz speed reference, but if it hasn't got a run command it won't run anyway. So perhaps the drive is having a 0Hz speed reference written, but there's a small amount of noise on the cable. If you had a 0-10V analog input zommanding 0-60Hz, you'd only need to see 50mV on the cable to make that "0Hz" actually be "0.3Hz".

The other thing to check is, which parameter is actually being displayed? It may be that all the other drives are displaying the actual speed, which will always display 0.0Hz when the drive isn't running, regardless of the speed command. Perhaps the one that's "flickering" is displaying the speed command rather than the actual speed, and just showing that very small amount of signal noise as described. You may find that if you change the other drives to display the speed command, they'd all do the same thing.
 

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