Analogue Reading fluctuate Problem

Dear All,

I have a problem of Analogue input fluctuation,and i have a few action without any success. I had done a few similar projects without this issue.

Please refer to the attached sketch of my design. Controlnet to link up with analogue input. The level transmitter is wired up with flexi io analogue.

The scaling is correct, but I am getting the fluctuation of around 2% although the current is measured stable. The tranmitter display reading is also stable, only fluctuate around 0.2%.

Some troubleshooting was done:
1. Improve on wire grounding with ohmmeter checked.
2. Direct sensor to analogue flexi IO.

All other site from the same PLC doenst have this issue.
Please help to advise if anything i could do with this?
Many thanks in advance for help.

Regards,
Jason

Nice drawing.

I assume the PLC to HMI link is not analog, it's some digital protocol?

Is the FlexiAnalogue-to-PLC link a digital protocol?

Is the output of DC power supply that powers the transmitters grounded?

Is the shield (drain) on the transmitter wiring cable grounded only at one end or both ends?

Is the transmitter (-) grounded at some point?

Is the input card a differential input card or single ended?

You might want to hook up an oscilloscope. I'd start at each transmitter and then work my way up. It is amazing just how noisy the world is. If don't see lots of high amplitude noise then your problem is not grounding. Make sure your conditions are normal when you check, ie run any motors, vfds, servo, etc. And answer each question that Danw asks.

Dear Danw & kb9ttx,

Thanks for you guys advice, I finally resolved the issue!
Apparently the DC power supply earth point was not linked properly the the earth bar in the remote panel. After we rewired the earth points, we resolved the fluctuation issue!

Big experience to learn here. Thanks a lot guys.

Regards,
sutton