Analog output issue

We are sending a setpoint to our Ozone generator using a 4-20mA signal from a SLC5/05 NO8I Output card .

The Wedeco Ozone generator receiving the setpoint has a Automation Direct PLC DL250-1 PLC -analog Input card is a F2-O4AD-1.

The system has been in use for 10 years . We have just started experiencing an unstable setpoint at our generator, the SP floats high and low then returns back to normal on random occasions . I used a Fluke 772 mA clamp meter to determine if the signal coming from our SLC is stable -it appears to be rock solid.the 24v power supply is perfect. Both ends of the belden are grounded.
No recent wiring modifications have taken place.

My question is ; I dont know whats going on ? is it noise the my clamp on meter can not detect interfering with the Automation direct PLC input .

Any help would be appreciated

Do you have Direct Soft software to observe the value in the D250 and RSLogix 500 to look at the value in the SLC?

A scope is a better tool to check for noise than a clamp-on ammeter.

Generally you only ground the shield on one end, not both.

Ah ok I'll take one ground end off the belden .Also I have both software packages , i'll observe both SLC and Automation Direct analog signals . We also have a scope we can try . thanks for the reply !

Scope is a voltage input. You’ll have to look at the voltage drop across a resistor to see what current is.

Connecting across the (+) and (-) of the analog input is probably the easiest way.

Use an LT comparison and a holding register to save the lowest value that the DL is seeing while it operates. Then you can come back later and see if its actually getting a droop in the analog signal.

+1 to Steve's single ended ground comment. loops will drive you nuts.
I have added isolators to 4-20 signals before to test for ground loops. Essentially 1:1 transformers they have shown me where a loop exists and I can trace it from there. Sadly they have been left there occasionally as time didn't permit other options.