Simple Rotation Sensing

Hi Guys,

I have a simple project but i think i need some ideas from you guys to help me get started. i need to install a rotation sensing circuit to a packing machine tape reel despenser that would stop the machine if the tape runs out, snapped, etc... machine is plc controlled and a sensor to be installed on tape reel holder is to be activated by a series of notches. everything is prepared apart from the very important one, i need help on building the ladder logic for this purpose. i hope you guys can give me ideas how to write the ladder diagram.
Cheers!

For this type of problem, I typically have a timer that runs when the sensor should be moving. The timer is preset to a value longer than the worst case time between the sensor changing states. I reset the timer with a 1 shot on each false and each true transition of the sensor. If the timer gets done, then the sensor hasn't changed states which indicates a fault.

What kind of PLC are you using?

OkiePC said:

For this type of problem, I typically have a timer that runs when the sensor should be moving. The timer is preset to a value longer than the worst case time between the sensor changing states. I reset the timer with a 1 shot on each false and each true transition of the sensor. If the timer gets done, then the sensor hasn't changed states which indicates a fault.

What kind of PLC are you using?

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thanks mate, i really appreciate it, its clear and very logical. i am using mitsubishi fx-on plc.

I use two timers one for N/O, one for N/C if the contact stays open or closed the appropriate timer will complete. Same as OkiePS's solution only different. We assume your pulse rates are low enough for the PLC to recognise.
Roy