Help Needed

Okay so I have a motor spinning a lets just call it a wheel that has a proxy cable, when it pulses 3 times that's one rotation. Now I've been given a range of 30 FPM to 600 FPM and I converted it to RPM's, RPM=(FPM*12)/(D*pi). The Diameter is 8 inches. I need a proficient way of telling the PLC when the FPM's or RPM's is down 70% it triggers a light indicating a slip alarm. Same thing for 50% it'll appear as a stall. I'm not to great with PLC programming. I thought about trying to make a counter that would reset every 20 secs that way one pulse would represent one RPM, and that would let the alarm know the count preferred failed, but I'm not doing something right. Any advice or redirection would be great thanks.

when you see a pulse, restart a timer, if timer does expire you are too slow.
for the 50% use other timer.

Shooter, I would need the pulse to count to triple these RPMS 287-200 on a 1 minute timer if I were to do it that way. How would you organize that on ladder logic?

I had a similar program but it had a different purpose. Since your already counting pulses I think it makes it easier for this sort of thing. You would use hi a speed counter totaling the pulses. There would then be a timer that would reset that counter after say 3 seconds. The number from the counter would then need to be saved and divided by the time set in the timer. This would then be your rate of change. Then doing some math to compare the last two value to determine if there a 30% difference to stop A.....

Greco,

Lets define what you have.
1. a motor running between x and y rpm. 3 pulses of a prox switch = 1 revolution. You have a formula to get the fpm.
2. a belt / conveyor running between 30 and 600 feet per minute.

The prox switch will tell you the speed of the motor for alarms as requested.

My question is - how do you get from the motor to the device that's moving 30 - 600 FPM? Belts slip, chains jump teeth, and so on. Is there a sensor on the moving system to tell you what the FPM is?

If the motor runs the same speed (assuming no variation) and the linkage from the motor to the device that's moving 30-600 FPM slips 50% lets say, how do you know its slipping?

regards,
james

This is to expand on what James McQuade said. If you are varying the speed, it would appear that you need two prox's, one to monitor the drive motor or driven belt pulley and one to monitor the non-driven or turn-around belt pulley. With that input you can then do the necessary calculations with the PLC. The drive motor prox will provide the target speed reference and the other prox will provide the actual speed reference.
Once we get the details resolved I will try to make a sample program for you. Do you have a particular brand and model PLC that you are using?

I would have to agree with JRW. Having a probe on each pully would be a lot more reliable especially if your setup has gearing. The logic is a lot more simple at that point you just get a ratio of the two speeds. Anything above 1 would be considered slippage.

The time between 2 pulses is enough to see the speed.

Yah you can also do it with one, but he probably has it pointed at the bolts holding the pully on which your then stuck with however many bolts there are.