allscott
Member
- Join Date
- Jul 2004
- Posts
- 1,332
I have a wire rope laying machine that has a spinning head that either 4 or 8 wires pass through to lay the rope.
This head travels up to 250 RPM and I would like to detect when one of the wires is missing. I’ve come up with a formula that I am calling Maximum Scan time (in ms).
MST = (1/(rpm/60)*number of wires)*1000
According to my formula with 8 wires and 250 RPM rotational speed the maximum scan time here would be 30 ms.
I will be using an SLC 5/05 with a fast input card as well as a high speed photocell. The SLC doesn’t have much of a program in it and very little I/O so I expect the scan time to be less than 5mS so I think that the combination of Scan time, turn on time for the eye, and switching time of the input card should be within reason.
I expect a square wave pulse train from the photo eye.
I am racking my brain trying to figure out how to detect when one of those pulses is missing ie: missing wire.
The PLC does not currently know the rotational speed of the head, nor does it know the number of wires.
The plan I have in my head is to calculate the running frequency of the pulse train and then set up a timer that will expect a pulse every X msec based on that running frequency. It should work in theory but the code is going to be messy.
Can anyone think of a better way to do this?
If your having trouble visualizing what I am trying to do picture a box fan with four blades and an eye watching the blades go around. I want to detect when one of the blades is not there.
thanks in advance
This head travels up to 250 RPM and I would like to detect when one of the wires is missing. I’ve come up with a formula that I am calling Maximum Scan time (in ms).
MST = (1/(rpm/60)*number of wires)*1000
According to my formula with 8 wires and 250 RPM rotational speed the maximum scan time here would be 30 ms.
I will be using an SLC 5/05 with a fast input card as well as a high speed photocell. The SLC doesn’t have much of a program in it and very little I/O so I expect the scan time to be less than 5mS so I think that the combination of Scan time, turn on time for the eye, and switching time of the input card should be within reason.
I expect a square wave pulse train from the photo eye.
I am racking my brain trying to figure out how to detect when one of those pulses is missing ie: missing wire.
The PLC does not currently know the rotational speed of the head, nor does it know the number of wires.
The plan I have in my head is to calculate the running frequency of the pulse train and then set up a timer that will expect a pulse every X msec based on that running frequency. It should work in theory but the code is going to be messy.
Can anyone think of a better way to do this?
If your having trouble visualizing what I am trying to do picture a box fan with four blades and an eye watching the blades go around. I want to detect when one of the blades is not there.
thanks in advance