VFD interference with labview

[RedneckNerd]

My hardware.

cDAQ-9174

  NI 9205  I have my signal coming in here 4-20ma with a 500 ohm resistor in parallel.

  NI 9213

  NI 9265

  NI 9485

VFD Optidrive E3

Labview 2014

The signal zeros out when I activate the VFD then climbs above the actual signal then dives back to zero.

It has done this in all connection senarios.

Originally I was controlling the VFD with the 9265 and 9485.  One was just a relay to activate and the other produced a 4-20ma signal.

I them tried controlling it from a USB-6009 to separate the signals thinking I was getting feedback or a ground loop.

I am now controlling it manually with a trim pot hardwired.  No connection to the NI hardware at all.

When reading the signal with a Fluke meter it is rock solid.  It is the NI hardware or labview that is having the problem.

As I have completely separated the VFD from the NI hardware I am at a loss.

I am sure it is some kind of EMI maybe on the building ground?  Any other ideas for me to look at?

Thanks in advance for any assistance.

[santo_13 · Accepted solution]

There are a lot of things electrically that could go wrong if connected incorrectly. Now, your post title is completely inappropriate as LabVIEW is just a programming language and you have used it to create application automation, in that case, the VFD can affect electrical parameters and not software.

Based on your description, there is something fundamentally wrong with the way things are wired. Please share a detailed circuit diagram of connections, manual for VFD. Essentially you used 4-20mA output with a resistor to create a voltage signal? depending on the VFD input type, this may not be suitable.

Please elaborate "The signal zeros out when I activate the VFD then climbs above the actual signal then dives back to zero."

• What signals?
• What is connected to these signals?
• Where does the 4-20mA loop get its power from?
  • What are the chances that the power supply is disturbed by the VFD injecting harmonics into the power line?

[RedneckNerd]

I have been tracing my wiring on the assumption that the problem is along the power lines or ground of the building.

I have made some headway by fixing a ground from my flowmeter to the power supply.

But to answer your questions.

The signal is from the flow meter which produces the 4-20ma signal.

I have a regulated dc power supply in series with the 4-20ma loop. It is properly grounded.

I am using the resister in parallel at the  9205 daq.  As you know this changes the signal from 4-20ma to 1-10vdc.

The power supply its self is producing a rock solid 24vdc.  The flowmeter signal when read by my fluke 87 is steady.

You are correct, my title needs fixed, it should read VFD interfering with hardware.

If my fixing the ground to the flowmeter doesn't solve my problem I will make a circuit diagram and upload it.

[RedneckNerd]

Turns out, it was a bad ground from the flowmeter.

I am even able to control my VFD from the other modules now.