PLC Programming

6/27/2011 2:48 PM EDT

What is the specification of the output signal of the rpm proximity sensor? Does the sensor provide pulses? or something else? If the sensor output is pulse train, then instead of a digital input card, it would be easier to measure the speed using a counter module available for your PLC. May I know the model of the PLC you are going to use?

6/28/2011 4:39 PM EDT

" I need the ladder diagram for the PLC, please help." Sorry to be a wet blanket, but you don't need this at all. What you need is an understanding of the problem, and of your PLC, so that you can solve the problem AND fine tune the solution AND fix it when it goes wrong.

Does your sensor emit one pulse per revolution, or a pulse train throughout the revolution? Either way, you need to measure the time between the pulses, and if it goes over a certain limit it will activate a contact. or take some other action, to "trip" the system as you wish.

So you need to get your sensor pulse to start a timer, and restart it every time a pulse comes in. If the timer times out, activate a contact.

As Sanjib says, if you have a fast pulse train you'd be better with a counter. Feed the pulses to a counter, check the counter value every so often, and if it is less than a preset figure (corresponding to your 15 RPM) then activate your contact. Reset your counter and start the process again.

Understand your problem, come up with a working solution, document it, and then if it goes wrong or you need to change it, you (or someone else, if your documentation is good) will be able to fix it easily.

Good luck!