4-20mA sensor in AI module

Please post a screenshot of your PLC hardware configuration for each of the analog inputs showing the input type (current / voltage), and then discuss the values you are seeing in the plc, and show us with a screenshot how you are scaling the analog signals in your program logic. 

Jay.

Hi Larry, thanks. I had wired the same way as you had mentioned. And like I said already three sensors are working normal. These three sensors are giving outputs, but the problem is just that at the values are not exactly correct. I had disconnected all the wires from the PLC now to see whether the current consumption by the Flow meters are creating problems. But verified that's not the case. Now I am going each channel diagnostic. Also I am wondering the problem might be the module itself. I ain't sure yet. Still in the process of figuring it out. Thanks for sharing your thoughts. 

Do yourself a favor - or humor me - and test a theory and also improve your project’s maintainability.

Create a DB to store your scaled analog input values. Add a tag for every analog input, datatype real.

Now replace all the MD0/MD4... tags with those db tags. It’s really quick if you name them all the same except the last character (you can rename later if you like).

Right-click on the plc from the project tree, Compile / download all.

Go online and monitor the tags and see if the oddities remain.

If they are gone, post a screenshot of your tag table so I can explain what I think happened.

...sent from App

Are all your devices 4-20mA?  Are some of them 0-20mA?

If you have some precision 500Ω resistors lying around, you can do the following for a test:

Change the hardware configuration for the analog inputs causing you problems to 0-10VDC.

Wire a 500Ω across the +/- terminals of the analog input.

With 4-20mA devices, it seems like they are loop powered rather than separately powered and providing a loop current signal for the PLC.

Is it possible a loose strand of wire is crossing terminals on some of the problem sensor wiring?

Yes, I had a guess that your scaling was going into overlapped memory.

Do you have a loop calibrator to use for calibrating the 4-20mA loop current inputs?

Jay.

I had did as you said. There is no change. still its kind of floating. But can you please tell what you were trying to say in your previous post? Is it about overlap of memory address which you think might have happened?