PLC Digital Input-Non Isolated

Hi All,

I have an AllenBradley Flex IO 1794 IB16, which is a non isolated 16 channel digital input.

I want to control a VSD and a DOL motor.

What I am intending to do, is to connect first 3 channels, so that the DI card sources the +24V DC.

For the rest of the channels, I want the VSD's control card to source the +24V DC.

I would connect both the VSD and the DI card's neutrals together. Would this work? Please refer to the attached schematic.



Thanks

I'm surprised that your VSD doesn't have dry contact outputs to take to your input card? That way you don't have to worry about input voltage. Can you give more information on yoru VSD and it's outputs to the input card? I'd be more inclined to have the VSD fire isolation relays and take the relay contacts back to the input card instead of tying the DC commons together.

Thanks for the instant response.. Much appreciated...


Yes, the drive does have relay outputs and they have been used for a different purpose.
The drive's 24VDC is used to for controlling the pushbutton start stop, etc and lot of wiring has been done already and I just didn't want to do a whole lot of rewiring. ( this is talking about 10 drive motor combinations).

this digital input ( Sourced from PLC ) is a new modification and I thought I could add it, without disrupting the existing system. Would this cause any issues?

thanks and regards
rvim002

It should work if you have the commons tied together. Typically my 24vdc common is tied to ground as well. It's not an ideal way to do it but it should work for you.

Thanks a lot Matt for your help...