SLC 5/04 and VFD problem.....need help

Guys,

I have this remote rack communicating with a SLC 5/04. There are several "Analog" output cards in this RIO that are being used to control VFD's on blower fans through a 4-20ma signal.

I have one of these cards that channel 3 is not varying the 4-20ma signal going to one of the VFD at all.The value is always 4.36ma
.
I already confirmed that the 1746-NO4I card is good by doing a swap with another one.

I also checked the PLC code to make sure that there was no issues in it.

Do you guys think that the actual rack for this RIO could have a problem which affects that particular channel?

Also, the VFD (Allen-Bradley 160 SSC) always display 50HZ in the front screen even do the 4-20ma signal is not working. I checked all parameters against other equal VFD's that are working and I can not find any differences between them.

Jose:
1) Disable analog output in the plc program, then create a new rung where you move several values one at a time to the same analog output while measuring with a 4-20 mA meter. If that is working then you have a problem with plc program.
2) If the vfd is showing always 50 Hz please then check VFD I/O, it´s posible that vfd is using fixed speed regardless of 4-20 ma signal.

I too think its running at a set speed. I assume the 4.36 is max set for the drive to catch up to? I would do the recommended rung test too.
Hope this helps! J

Are you sure the analog command is wired to hte right input on the drive? 4-20mA signals should be wired beween terminals 3 (common) and 4. This is how the drive would react if you have a current signal feeding a voltage input.

Keith

Thank you guys,

Widelto, you are suggesting to turn off the piece of code that sends the 4-20ma currently to the 1746-NO4I card and then manually put numbers that represent current amd measure with a meter, right.

jose: That´s correct

A quick update that I feel soo embarrase to report but it turn out that the 160 drive we had controlling this blower motor was the wrong one. The 160 drive was a "Preset Speed" model instead of an "Analog" model.
When I was measuring the amps going into the VFD, I just broke the loop between the VFD and the 1746-NO4I card and added the meter and due to the wrong type drive it was causing the strange behavior on the 4-20ma signal.