ab 1756-IF16 separate dc inputs

I have an existing 1756-IF16 wired as single ended with all RTNs tied together. Channels 0-3 have 2-wire loop powered devices connected with all from the same 24vdc supply. I want to connect three (3) additional devices that are currently powered by 120v sources which provide 24vdc powered 4-20ma outputs. Do these new inputs need loop isolators being that all are powered from different 24vdc sources. Thank-you

tlona said:

I have an existing 1756-IF16 wired as single ended with all RTNs tied together. Channels 0-3 have 2-wire loop powered devices connected with all from the same 24vdc supply. I want to connect three (3) additional devices that are currently powered by 120v sources which provide 24vdc powered 4-20ma outputs. Do these new inputs need loop isolators being that all are powered from different 24vdc sources. Thank-you

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The short answer is 'Yes'.

The idea is to send the 3-wire or 4-wire signal (from the separately powered devices) to one side of the isolator, while the '2-wire' part of the isolator is wired to the IF-16 like any other 2-wire device.

That said, I have yet to get that working as described. I tried what I described above with 3 different brands of 4-20 mA isolators. And I failed. I ended up adding a separate IF16 wired as 8 isolated inputs. That works fine but cost me another IF16 and another slot in my rack.

Good luck and let us know if you it working

tlona said:

I have an existing 1756-IF16 wired as single ended with all RTNs tied together. Channels 0-3 have 2-wire loop powered devices connected with all from the same 24vdc supply. I want to connect three (3) additional devices that are currently powered by 120v sources which provide 24vdc powered 4-20ma outputs. Do these new inputs need loop isolators being that all are powered from different 24vdc sources. Thank-you

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It depends upon the instrument. Four wire instruments with isolated outputs should co-exist peacefully with two wire instruments on the same module, and most (but not all) modern instruments do have isolated outputs.

Thank-you All for the response. Yes I have some that have isolated outputs but others do not.
'thingstodo' what loop isolators did you try. I typically would use the eurotherm WV408-200 ultra slim pak II. I have not used in this setting though