0-10V Signal Variations

I am having an issue with speed variations on a Vacon X4 drive running a product pump and we are not sure how to verify what the problem is. The 0-10v signal coming from the SLC 1746-NIO4V is stable when measured across the wires while connected or disconnected, but measuring the signal against the drive’s ACOM terminal causes the fluctuations in the voltage. I tested the VIN status while connected to a potentiometer using the drive’s internal 10v signal and did not see any fluctuations. the range of the fluctuations is .3v which is significant enough to produce flow rate variations of 7gpm and affects our pasteurization temperature.

How can I verify the problem is with either the VFD or the NIO4V?

Kpdaughtry said:

I am having an issue with speed variations on a Vacon X4 drive running a product pump and we are not sure how to verify what the problem is. The 0-10v signal coming from the SLC 1746-NIO4V is stable when measured across the wires while connected or disconnected, but measuring the signal against the drive’s ACOM terminal causes the fluctuations in the voltage. I tested the VIN status while connected to a potentiometer using the drive’s internal 10v signal and did not see any fluctuations. the range of the fluctuations is .3v which is significant enough to produce flow rate variations of 7gpm and affects our pasteurization temperature.

How can I verify the problem is with either the VFD or the NIO4V?

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how long of a run is this? what other wires is it being ran with? what kind of wire is it being ran with?

Noise induced into any analog inputs is going to cause fluctuations, and you probably want to try to use 4-20ma signals when possible, 0-10v is really only decent when it can be isolated easily from other sources of power and its all within the same cabinet. imho.

I just verified the wires by running a jumper outside the panels and saw the same behavior. There is another 0-10v controlled vfd right next to it with the signal coming from a separate PLC through the same conduit and it is not fluctuating. The cables are shielded and grounded and the run is about 50 ft. The conduit it runs through is shared with 120VAC and 24VDC control wiring but nothing high voltage.

I understand the benefits of using 4-20mA but would need to convert the PLC card to change it as the output is currently limited to 0-10v only. We have many setups similar to this in our facility that are not causing issues. There is even another one running on the second output of the NIO4V that is showing no fluctuations. This is why I haven't just changed the output channel yet, if it was open I would have done so.

For the sake of simplicity please assume the system design was functional in the past as it has been unchanged for more than 10 years. To my knowledge the fluctuations have never been this bad though I only inherited the responsibility for the controls three years ago.

I found an open channel on a nearby PLC, ran a cable to the drive to monitor the input status, and found no fluctuation in the signal. We only had two used NIO4V cards on hand and all three show some fluctuation but one only had .1v which is better than the .3v we have been seeing.

I found out the NIO4V is discontinued so hopefully we can get the system upgraded soon.

IanM8040, I apologize if I came off short or rude. I appreciate the input and I thank you for your fast response.

vfd's are notorious for creating noise.
if you are unwilling to go to 4-20 ma, get a cable with a 2 twisted pair of wires that is also shielded with drain wire . on the end next to the drive, wrap the drain wire around the cable 5 turns and use shrink tubing on that end. take the other end and ground the shield on the analog output card at the shield terminal. also, you should use vfd to the motor.
what is the voltage?
if it's 480 and the run is longer than 50 ft, you need a line / load reactor.
james

This sounds like a voltage output and an input that are not truely isolated, and which are being affected by the zero volt potential not staying fixed. I've seen this a fair bit with danfoss drives when both an analog input and output on the drive are used by the same PLC.

I would add a loop isolator at the PLC card end. You get models which can take 0-10V in, and push 4-20 or 0-20mA out. Easy enough to do a test, and they are not costly.