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Hello,

I have inherited this problem that has been plaguing this system for 4 months.

The customer wants us to swap out for AB or Siemens, but I think this should be correctable.

 

I have the following hardware...

 

V200-18-EB6

EXL-CAB295

EX-D16A3-R08

 

These black screens only appear 1-20 minutes after a 3 HP VFD and pump starts up.

 

We have ferrite coils on the 24 VDC going to the V570.

 

Everything I have been told points to noise.

 

Where should I start? Zener Diodes?

 

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Thank you Flex727, I will follow your suggestions.

 

I should add, that after this happens, power cycke, and V570 operates normally until the second VFD is started again.

 

Could be vibration, will check that.

IS there a good source on where to add snubber or zener diodes to the IO into the snap?

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  • MVP 2021

You're on the right track, but zener diodes are not the answer.  You need something to filter out the frequencies the VFD is generating.  I did a retrofit project once where the customer pulled all their wires in same conduit - VFD controlled motors and 24V I/O.

I put a scope on all the points on the PLC and found large 4KHz noise on all the inputs, which will put the PLC into crazy mode.

My solution was to put an external 0.1 uF capacitor on each I/O point to ground.  Inputs and outputs.  Unitronics does not build filters into their modules.  Looked like crap, but it knocked the noise down enough for the system to run.

If you have a scope, poke around with it and see what you can find.

Joe T.

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15 hours ago, Ausman said:

Is the VFD, or any of it's controlling contactors etc apart from signal switching, in any plc component enclosure at all?   Where's the expansion cable running?

Aus

Thanks for taking the time to reply Aus!

The PLC is in its own Enclosure.

The VFD is a Grundfos/Danfoss IP67 Skid mounted unit outside the control panel.

Please see attached picture.

I do not like plastic enclosures, but these are the cards I was dealt.

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20170315_153115.jpg

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11 hours ago, Joe Tauser said:

You're on the right track, but zener diodes are not the answer.  You need something to filter out the frequencies the VFD is generating.  I did a retrofit project once where the customer pulled all their wires in same conduit - VFD controlled motors and 24V I/O.

I put a scope on all the points on the PLC and found large 4KHz noise on all the inputs, which will put the PLC into crazy mode.

My solution was to put an external 0.1 uF capacitor on each I/O point to ground.  Inputs and outputs.  Unitronics does not build filters into their modules.  Looked like crap, but it knocked the noise down enough for the system to run.

If you have a scope, poke around with it and see what you can find.

Joe T.

Thanks so much Joe.

 

I am going to site with a Fluke on Monday.

 

I am also going to Sayal to pick up some 0.1uF caps.

 

So basically put the cap between each digital IO point and ground if I see noise on those wires?

 

I also am using some analog...and suggestions for that?

 

THanks again Joe!!!

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  • MVP 2021

Photos are useful things.  +1 to everything Joe says....I was thinking that was a bit further down the track.

If these are plastic enclosures, and looking at the general layout and size of the VFD, everything is still way too close together for my liking.  A few more comments.

The expansion cable being a long one must be one of the cables coming out of the bottom.....and likely into the same cable duct the vfd wiring is in.  Can this be separated out into it's own run?  And where is the other end located?  Right next to the pump???   In another plastic box???  Hmmm!!!

It looks like there will be other control gear in the enclosure with the isolator on it.  If this is so, then perhaps a neat earthed metal plate b/n it and the plc enclosure would help.  It could also be folded and shaped to go around the bottom of the plc box as well for better protection from the VFD.  Alternatively, change the plc's enclosure to metal!  And perhaps...the VFD might not be the real issue....it might be a big contactor banging on, which if in this enclosure is right next to the plc.  Or a combo of both things.

All control wiring should be separated out as much as possible.  If there is any in a duct that the vfd uses, change it.  The only time I've had to have a VFD in the same enclosure as the control gear, I made special shielding plates to essentially have the drive in an enclosure within the enclosure, and wiring was totally separate.  Have had no trouble with this.

Analog in correctly shielded cable and run on it's own.

Joe's "looks like crap" filtering ideas could perhaps be tried if, after fixing the more obvious layout errors, you still get lockups.  As he says, put a scope on it and see, but perhaps try all the other solutions first.  Proper layout preventing the noise in the first place is far better.  Scope before and after basic layout changes would be useful, and show the client something tangible as well.

Lastly, is the motor on the pump one specifically designed for VFD running?  Something else to consider.

cheers,

Aus

 

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4 minutes ago, Ausman said:

 

We only get the Stop Error when the Grundfos VFD starts, so I am 99.9% sure this is VFD noise causing the Stop Error.

I am not exactly sure where they ran the expansion cable, but I will find out on Monday when I get to site. If it is running anywhere new VFD or power cables I will space it out.

I have a fuke 125B scope, so I will be probing for noise on all the snap IO and basically all the connections to the 570.

I hate plastic enclosures as well, they have no place here, again, cards I was dealt.

I will post some more pictures....

 

Yes, Weg motor is VFD rated, 0 turn down.

 

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30 minutes ago, Flex727 said:

I still say it's vibration with the Snap-In module. I've seen it happen more than once and I got those exact same errors.

I was actually looking at adding the 4 holes in the snap IO (yes...void the warranty) and add some self tapers to hold the IO snug.

 

Thanks Flex727

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32 minutes ago, Flex727 said:

I still say it's vibration with the Snap-In module. I've seen it happen more than once and I got those exact same errors.

Also, apparently the Stop Error happens several minutes after the VFD/Motor is running, which would lean towards vibration?

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I have been talking to our local Uni dealer.

He gave me some varistors to try, also some 120ohm and .1uF caps.

Of course I will try to eliminate at the source, but if I can't has anyone added these types of noise filters to the Snap IO points?

I will post some noise pics next week!

Hope everyone has a nice weekend!

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