Changing to Non Isolated AI 1794

[throughput]

Hi all, please comment on the impacts of changing from isolated analog inputs to non isolated analog inputs. This is for an existing Rockwell 1794 Flex IO system that currently uses 1794-IF4I 4 point islated analog input cards. The rack has the max of 8 cards and we need more analog points. We are looking at changing the 4 point cards to 8 point or 12 point non isolated analog inputs 1794-IE8 or 1794-IE12. The existing inputs are 4-20mA. What are the disadvantages? Is this a simple change, un-terminate replace card, and re-terminate? Any other ideas?

 

[dmargineau]

I would first look into the reason why isolated analog input modules were originally used; an isolated analog FLEX module is some three times more expensive than a "generic" one and you wouldn't think someone would spend three times more than needed.
One of the reasons one would use isolated analog inputs is the fact that the said input devices' supply power is external to the modules' one.
You could replace the isolated modules with "generic" ones only if the modules' power supply could withstand the additional load and if the devices could use the same voltage levels as the one used for the modules.

 

[Bit_Bucket_07]

If you are using any non-isolated instruments, then you'll need to purchase isolation transmitters for them.

 

[BobB]

If you are using any non-isolated instruments, then you'll need to purchase isolation transmitters for them.

Here here - if loop powered the damn things interfere with each other and you get dud readings without isolators.