Mixed Voltages for a Compact I/O system

[Dryhops]

I have a system that is all currently 110 AC. It uses a 1769-L30ER with a 1769-PA2, and a 1769-OA8.

I need to add 4 2-wire pressure transducers that require 24v. Can this be done by adding a 1769-IF8 and then using an external power supply for the DC+ to the transducers?

I really only have experience using 24v systems and stepping up voltage with relays, not the reverse.

Thanks for your time.

 

[scott.lawrence]

you would have to have the power supply, since that module does not provide loop power




https://literature.rockwellautomation.com/idc/groups/literature/documents/in/1769-in067_-en-p.pdf

 

[Dryhops]

True, I know I must use a separate power supply I have read through the document you linked.

I guess my question then becomes, is there an issue returning a 4-20mA signal at 24v to a 1769-IF8 which is connected to a 120v compact I/O rack?

 

[scott.lawrence]

no, it's done all the time

 

[Jeff23spl]

your 120v is going to the PA2 power supply but all modules work with 24v or 5v from that power supply. That PA2 isn't made to power your probes so you need a separate one for this as you plan. It is the proper way of doing it

 

[Dryhops]

To clarify, every module is being supplied 24v backplane power? So in the case of my 1769-OB8, looking at the wiring diagram, I'll be running my L1 to the module which will supply 120v to whatever (pilot lights in this case), but the module is actually running at 24v along with the PLC?

 

[Helliana]

The 1769-PA2 is the powersupply for the PLC. It converts your 120VAC to 24V and 5V DC to power the PLC and all the cards on that section of backplane. Even the 24V powered model power supplies do the same thing.



This powersupply is only used to power the PLC processor and I/O cards, not any field devices. You will need to use seperate an external power supply to provide power to your sensors.

 

[Jeff23spl]

There is a 24vdc from the PA2 powersupply that just power the brain and internal needs of each module.
Then each of them are different with the respective signals and module type used.
The IF8 is a passive one that will receive a powerered analog signal but according to your 2 wires system, you need a separate powersupply to power the loop.
In the case of the OA8, it also get it's internal power from the pa2 power supply but it trigger some kind of AC triac that you can connect with your 120v source on one side and get the source switched on each respective output. It is 2 isolated thing inside the same module like a 24vdc relay to drive 120v ac load but it is an electronic device instead of a relay