# Frequency Formula Question

#### ironmike828

Joined Jan 29, 2010
13
Hi Everyone,

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?

#### Papabravo

Joined Feb 24, 2006
14,865
1600 counts/minute ≈ 27 counts /second
This is roughly equivalent to 53 Hz.
At this frequency there are no frequency effects you need to worry about.
What you do care about is IR looses going from the source to the sink and ground return losses from the sink back to the source.
You need to measure the transmit levels at the source (High and Low), and you need to measure those same levels at the receiver.
Then ask yourself the following questions:
1. Is the received High level significantly above the receiver threshold for a logic 1?
2. Is the received Low level significantly below the receiver threshold for a logic 0?
If the answers to both questions are yes then you are off the hook unless you discover new evidence that something is wrong.

One more thing:
Rise and fall times should be less than about 200 μsec.

#### ramancini8

Joined Jul 18, 2012
473
If your detectors are edge sensitive you need to consider the length of cable, signal quality, and signal strength.