Powerflex 40 erratic behavior.....

Guys,

Does anyone has an idea why a group of conveyors running on Powerflex 40 controlled by analog signals could be going into erratic acceleration and decelaration. It happens sometimes, not always.

Is the analog circuit overloaded? We had a system that would run steadystate no problem. When we exhale my current went to have a load of the supply. A simple power supply change took care of the problem

So the DC power supply had an effect on the analog signal use by the VFD's.

We have a very old 7.2 Amp power supply and about 15 VFD's or so driven by an SLC 5/04 on this particular machine.

JeffKiper said:

Is the analog circuit overloaded? We had a system that would run steadystate no problem. When we exhale my current went to have a load of the supply. A simple power supply change took care of the problem

Click to expand...

Jeff are you trying to be funny here
or is it just poor wording choice?

Dan Bentler

JoseM said:

So the DC power supply had an effect on the analog signal use by the VFD's.

We have a very old 7.2 Amp power supply and about 15 VFD's or so driven by an SLC 5/04 on this particular machine.

Click to expand...

Jose
Check the temperature on the power supply - if just warm to touch probably OK. If any doubt check current and voltage on output under full load and as used conditions. Yes if overloaded and voltage droops far enough it could be your problem

Dan Bentler

leitmotif said:

Jeff are you trying to be funny here
or is it just poor wording choice?

Dan Bentler

Click to expand...

Voice to speach didn't work on that one. We had different PID loops for each drive. The power supply was 3 amp when 2 or 3 drives would accell at the same time the loops would drop to below the exceptable voltage. We changes it out to a larger supply both in current and voltage. The problems went away.
These where old reliance drives the kept adding drives and adding drives to the system.

This sounds like a conflict between the various commons on the drive's analog inputs. This will occur if the analog inputs are not completely floating which forces the loop power supplies to all have the same common.

If the power supplies are also being drawn toward other common references, a conflict between the references occurs which can overload the power supplies, cause the inputs to misread the signal and a bunch of other confusing things.

The solution, if the PF40 analog inputs are not floating is to install a signal isolator before each input to break the commons.

Dick,

Can you explain your suggestion some more? I'm a little confuse about "Analog Inputs Floating".

I have output cards that are sending the analog signal to the VFD's base on an array of sensors that I'm monitoring on a conveyor.

I'm probably asking something that has already been checked but ... have you verified that the signals to the analog outputs are not varying due to unexpected input conditions? If you set the output to a constant do you still get the variance?

Bernie you take all the fun out of it. I ASSuMEd that that wasn't a problem. What is that old rule KISS. Sometimes my mind just jumps to those extremely odd scenarios. You where the ones where you learn the gateway and finally get it.those get locked in the gray matter and very seldom get forgotten.

Sorry to revive this old thread but I want it to double check on something. I have a question, when you guys are talking about DC voltage, are you referring to the "Start" signal on the VFD? The reason I ask is because the way this drives are setup is by using its own "DC Signal" and running it through a 120Vac coil relay that is control by the SLC 5/04.


If this is the case, does the DC power supply can still be consider a potential cause to the problem with erratic accel and decel on these drives.

DickDV, What exactly is it happening with the analog input signal to the drive that you mention. Also, how can I tell if the analog inputs are floating on the drives that are being control by this SLC 5/04. DO you know of a good "Signal Isolator" I could purchase to test on these drives?

If a VFD or any other type of electrical equipment has multiple signals coming into it and it's inputs all have one side (usually the negative) tied together, then you have forced each piece of equipment which is sending a signal in to have the same common. Some signals are referenced to different potentials and when all are tied together, they conflict with each other. You can get unexpectedly high currents or even fuses releasing. If any of the signals have an AC reference to any other signal, the AC may appear in the signal causing even worse problems.

To avoid this, some VFD manufacturers float their multiple inputs and outputs with optic isolators and similar circuitry so this conflict doesn't occur.

If your equipment doesn't float its inputs, then there are devices that will "float" each individual signal. They will be 0-10V in, 0-10V out, 4-20ma in, 4-20ma out, or any other configuration but the important part is that they isolate both sides of the signal from any other reference so they can be attached to an input with a forced reference and no conflict will occur.

I rarely have to use such devices but I think Action Instruments is one source for these. I'm sure if you Google "signal isolator", you will find more.