I have a question, I'm not sure how to look up a formula to prove a circuit for a project I'm working on.

Currently we have a 24VDC Photoeye detecting objects at 1600/minute. The input of the photo eye goes to a RedLine Counter which keeps a running count displayed.

We would like to run that signal in parallel with the counter and take the signal to a PLC input (High Speed Counter Card). The basic question is if we assume we run the cable 50 feet, or a 100 feet will the two signals in parallel pull to much current from the Photo eye and also will the frequency be distorted?

I'm not sure where to even look for the frequency distortion formula. Any hints on what type of formula I should be using?