Error in readings on FP AI 110

[StellaD]

Hi,

I am trying to use an AI-110 to read a 4-20 mA current source from a device (pressure transducer). It appears to be working fine on some channels but not other channels. When I use these "bad channels" all the channels read incorrectly.

Since the kit is old I am trying to figure out a) why this happens b) if there are any cures c) how to prevent similar things from happening. 

Also when using there field point to measure from one of my more sensitive devices it caused my transducer to overload. I think my wiring was correct ( DMU 10 AFRISO  http://www.afriso.de/servlet/com.itmr.waw.servlet.FileViewer?dokmanid=416996&kdid=256967&sprachid=1) since it is two wire system the +supply was connected to Vsup and the negative supply was connected to Iin.

I have tonnes of questions for anyone can and is kind enough to take the time to answer:

1. Are these channels permanently damaged? Is there trouble shooting procedure to verify if these channels are bad?

2. Do I need to connect the earth from my coaxial cable a earth ground before reading it into the AI 110 module?

3. The operating instructions say to install 2A fast acting fuse. Is this to ensure human beings don't get killed? Is there a type of fuse to place onto the Vsup and Iin of the field module to prevent my expensive equipment from being accidentally damaged and the FP module from being damaged? 

4. Does a 4-20mA loop isolator gain me anything?

5. Does the COM channels need to grounded to prevent this cross talk? 

 Thank you in advance!

Stella

[AndreaN]

Ciao Stella,

let me give you some answer:

-Are these channels permanently damaged? Is there trouble shooting procedure to verify if these channels are bad?

To figure out if the channels are damaged you can do a simple measure of a known voltage or current. You can use a generator and then by measuring the AI channels of the module you shoudl be able to tell if some of them are damaged.

- The operating instructions say to install 2A fast acting fuse. Is this to ensure human beings don't get killed? Is there a type of fuse to place onto the Vsup and Iin of the field module to prevent my expensive equipment from being accidentally damaged and the FP module from being damaged? 

The fuses prevent the FP modules from being damaged 

- Does the COM channels need to grounded to prevent this cross talk?  

 you can take a look at this tutorial about issues with analog input measures:

http://digital.ni.com/public.nsf/allkb/B9BCDFD960C06B9186256A37007490CD?OpenDocument

Hope this can help,

Ciao!