TAC I/A series MN 200 communication drop

[Gopal1977]

I  am using the controller TAC I/A series MN 200 in a project. I connected VFD- Brand (LS) model G100, H100, IG5A, IS7. Totally there is 56 VFDs with different KW ratings connected through 7 networks, connect and controlled at the central monitoring station. Normally this system is communicating, When the VFD is ON within a minute the communications lost. once VFDs off the communication is re-connected. The TAC I/A series MN 200 analog output 0-20mA is connected to VFD analog input.

Below are the solutions i tried to solve

1. Installed Analog barrier/isolator device 4-20ma between the controller and VFD.

2. Separated/ segregated the power and communication cable.

3. Screened Communication cable used and properly ground.

4. Disabled VFD EMC selection off.

still, the communication drops exist.

If anyone has a solution please support.

[CraigEl]

Clearly the VFD is the issue here, I have seen issues when the VFD or building earth is inadequate and unable to reject the noise generated by the VFD which then causes corruption of anything connected to the same earth. I have also seen issues if the connections between the VFD and the motor are not run in screened and properly earthed cables. These become a huge antenna for the noise generated.

The first step in the process is to examine the VFD installation to make sure that the items above are correct.  

Make sure that the VFD has chokes fitted, for some brands this is an optional extra.

Examine the earth, power and communications with an oscilloscope with the VFD both off and running.

I have also seen improvement by earthing the LON shield with an R/C network as noted in the following extract from the Echelon FTT10 Transceiver user guide.

[Troy_Wecker]

Excellent response from CraigEI.   My experience with VFD products is that they can cause issues by feeding back interference on the AC power lines to the products.   That can disrupt digital signals and communications elsewhere if not mitigated.