product surveillance

Hello to everyone,
I have a question about an alternative way to program a PLC for the application I have
This machine has a surveillance system monitoring for the presence and gap between products as they flow through the different stations in the machine. It uses flags on a shaft to trigger a couple of inductive sensors and photo eyes per station tracking the product.
It all works fine, however I was trying to use only 1 flag (reduce the clutter) as a pulse (1/rpm) and then using some logic to check if all the different PE's changed state accordingly, if not, then stop the machine
Any Ideas??

Thank you

Paulo

Hi Paulo, I think you are looking for a "Programmable Limit Switch", or PLS. These trigger the machine events based on machine rotation, and not based on time as you are suggesting. Using timers to do this application in PLC software is not a good idea because it creates a dependence on machine speed that your current control system does not have. PLS's require an encoder on the shaft, in addition to the hardware and or software for the PLS itself, so I'm sure that a couple of proxes will be a much more cost effective, simpler solution.