vfd triggering inputs

bbseay · Apr 16, 2005

Whenever my vfd kicks in it makes a few inputs come on and fault out my program. I am using everything AD. vfd is not in the plc panel, but inputs, outputs, and vfd outs are in the same conduit going to the machne 40 feet away. where in the system could the interference be coming from?
TIA

Billy Seay

504bloke · Apr 16, 2005

You need to seperate the VFD from the low voltage signal wires

VFD cable should have a screen

Thomas Sullens · Apr 16, 2005

ok

Billy I wouldn`t run the controls with the motor leads. Some say you can, but if you want to be safe then don`t. Here`s some other thoughts on this and this may not be your problem so here we go it could be???
http://www.plctalk.net/qanda/showthread.php?t=12827

:site:

DickDV · Apr 16, 2005

bbseay, keeping this as simple as possible, the leads from the output of the vfd to the motor are terribly noisy. They must be separated from all other wires including power wires ideally.

That's by far the most likely source of your problem.

Lancie1 · Apr 16, 2005

bbseay,
Let us clear up the confusion. When you said "inputs, outputs, and vfd outs", I think we mostly understood that by inputs and outputs you meant the PLC I/O, but exaclty what did you mean by "vfd outs"? Are you referring to the PLC outputs that control (start/stop, change speed) the Variable Frequency Drive?

bbseay · Apr 17, 2005

vfd to motor outputs

rsdoran · Apr 17, 2005

As was stated, move your motor leads or screen them from any other wiring. VFD motor outputs creates harmonics which in turn is noise (voltage) induced into other wires and can create false signals.

Terry Woods · Apr 17, 2005

It appears that there might be an "assumption" happening here...

Has this drive ever worked correctly?

Is the program "known" to be good?

Are you using "outputs" from the drive to send "input" signals to the PLC?

If so, what are those "outputs"? What "signals" do they provide?

Are these programmable outputs? Are they configured properly?

Could the problem be something as simple as looking for the "Running" signal as soon as the "Run" signal is sent? (i.e. before the drive can turn on).

A little clarification with respect to the inputs and outputs would help a lot.

bbseay · Apr 17, 2005

Terry
the inputs that are triggered are prox's. they are on a moving gantry. the contol wires are ran through conduit to a festoon system. there are inputs, outputs and vfd to motor connection in the festoon.

the program is designed that when certain prox's are on at the same time they make it a fault condition.the vfd's are new, everything is new. if i unplug the vfd to motor connections the interference stops. i can watch the input card lights and when the vfd kicks on most all of the prox inputs flickerand registers on the plc. I am using dc inputs---relay outputs

bbseay · Apr 17, 2005

would line reactors on the output side of the vfd help reduce interference any?

Alan Case · Apr 18, 2005

Quick and dirty fix
Use the input wires to pull in relays and then use a set of the relay contacts to drive the input. Induced noise wont pull in the relay. Regards Alan Case

Ken J · Apr 18, 2005

Take a look at the I/O signals with an O-Scope to get an idea of the level of the induced noise. Take a few minutes to try a simple capactive filter and/or reverse biased diode to reduce the noise. Don't spend too much time doing this if it doesn't show immediate results.
Reactors are expensive and take up a lot of space. You may want to run a quick test to demonstrate separate wiring would actually solve the problem. Try running wires from one of the prox's to the PLC and just let them lay on the floor and see if that works. If it does, the best solution would be to separate all the VFD wiring from I/O wiring.

rdrast · Apr 18, 2005

If you are absolutely stuck running things together in a festoon, you may have to switch to fully shielded cables, for motor leads AND control signals (seperate cables, obviously).

vfd triggering inputs

bbseay

Member

504bloke

Lifetime Supporting Member

Thomas Sullens

Member

DickDV

Member

Lancie1

Lifetime Supporting Member

bbseay

Member

rsdoran

Lifetime Supporting Member

Terry Woods

Member

bbseay

Member

bbseay

Member

Alan Case

Lifetime Supporting Member

Ken J

Member

rdrast

Lifetime Supporting Member

Similar Topics