Output from plc1 to input of plc2

output from ab slc 500 to an input on an ab micrologics. Output and input are pnp and 24vdc. Voltage is coming out of output fine, but when i go to the seperate control panel with the compact logics plc, then i dont read the 24vdc coming into input. I wonder if it is a different of power supplies... Thus i would either need to use relays, or maybe i could tie the negatives of the separate power supplies together(would be easier)? Would tieing the negatives together cause an issue?

Your thoughts? Thanks in advance.

Without knowing what cards are in each device, and how it is physically wired, this will be tough to answer. you also mentioned three different plc's (slc,micro,compact logix)?

If you want a simple answer.

run the output to a slave relay, using that panels power requirement. Run the contacts from that relay using second plc's power requirements to the second input.

Does the signal wire have continuity? Is plc2's input wired to common? Does that wire have continuity?

If the 24VDC common on both panels are connected, all you have to do is to connect one wire from the output of one PLC to the input of the other PLC.
If not, you must use a relay like Robo77 posted.

Most likely it's a sourcing/sinking problem.. Check the internal wiring of the modules and you will find your answer there.. The simplest way to do it is put a interface relay in between and it should work..

Kinda an odd application. Typically a PLC output isn’t tied straight to another PLC’s input so you do have to be careful. If it is truly 24VDC out to a 24VDC input then the common’s need to be tied together. I wouldn’t rely on the panels having a common ground although having said that if you tie the commons together you better make sure the panels chassis grounds are also tied together or you run the risk of damaging one or both of the PLC’s.
I’d recommend that you provide a lot more detail like the model number of the inputs and outputs (or in the case of the MicroLogix the model for it). It will be easier to figure out what will and won’t work from there.