analog flex I/O to VFD

[jcole28 0]

The attached files shows analog terminations from flex I/O modules to VFD. I have someone telling me that I should use isolated cards instead of nonisolated cards. I don't see any possibility of noise or ground loops. Why else would I use isolated over nonisolated? Am I missing something? Do you see a problem with the terminations? I am not familiar with flex I/O but it doesn't seem any different than any other analog modules that I have installed. There are also three 4-20mA devices connected to analog input card. The VFD has 0-10V analog output that is connected to a different channel on the same flex I/O input card. I don't see this being a reason to isolate though.         

vfdvfd.pdf

[AndrewG 13]

2 hours ago, jcole28 said:

. I have someone telling me that I should use isolated cards instead of nonisolated cards.

I would ask this person why they think you need an isolated card.

The drawing is a little hard to read.

I'm not that familiar with isolated vs. nonisolated, but in my experience: I have mostly used nonisolated cards (CompactLogix) because they are easier to wire. Also I think the nonisolated ones were cheaper (I could be wrong). But a few times we specifically used isolated cards because we knew we were going to have noise issues.

[Joe E. 259]

Non-isolated modules are cheaper than isolated ones for the same number of points. We have several machines using non-isolated Flex analog inputs/outputs that have a mix of +/-10V and 4-20mA signals with no issues.

[pcmccartney1 141]

Seems to me, it has mostly to do with noise immunity and bleed over from other signal wires or power wires.  The other change is if you are working in explosion proof areas and a need to install isolation barriers or hockey pucks.

[jcole28 0]

Just curious Joe.  Are the field devices providing loop power or the flex I/o input cards or an external power supply?

Edited 30 Jan 2018 by jcole28

[Joe E. 259]

Most of the time it's an external power supply but in one application the field device provides the power (that one has 3 output channels configured for +/-10VDC). Most of our 4-20mA devices use external power supplies.