Timer Trouble for ML1200

[Eric Nelson]

I'm a bit late to this thread, but here's a few observations on the latest version...

The 'Hoist Position' counter can easily get out of synch by repeated pressing of the fwd or rev buttons while at the 'on station ls'. Might want to make the 'on station ls' a one-shot (and debounce that input if needed)

The 'hoist lifting' and 'hoist dropping' bits can BOTH be on at the same time if the operator reverses direction before reaching an end sensor. Adding an XIO 'down pb' before the OTE on rung 3, and an XIO 'up pb' before the OTE on rung 5 is one solution.

Since the up timer's .TT bit 'seals in' the timing rung, it will continue until the up timer expires (32767 seconds later). You will need a way to reset the up timer when the operator removes the basket.

Since I see no physical outputs being used, I'm guessing this is just monitoring the system?



-Eric

 

[ceilingwalker]

I'm a bit late to this thread, but here's a few observations on the latest version...

Better late than never. The greater the number of people that reply, the more I learn.

[/quote]The 'Hoist Position' counter can easily get out of synch by repeated pressing of the fwd or rev buttons while at the 'on station ls'. Might want to make the 'on station ls' a one-shot (and debounce that input if needed)[/quote]

I have been having trouble using one-shot's with the ML1200. It doesn't seem as flexible as using them on a SLC processor. I don't know what you mean by a "debounce" input.

[/quote]The 'hoist lifting' and 'hoist dropping' bits can BOTH be on at the same time if the operator reverses direction before reaching an end sensor. Adding an XIO 'down pb' before the OTE on rung 3, and an XIO 'up pb' before the OTE on rung 5 is one solution.[/quote]

Thank you for pointing this out to me. In the original program the lift/drop outputs are preceeded by a permissive string of instructions and one of those instructions prevent them from happening at the same time.

[/quote]Since the up timer's .TT bit 'seals in' the timing rung, it will continue until the up timer expires (32767 seconds later). You will need a way to reset the up timer when the operator removes the basket.[/quote]

At the rungs immediately following the process timers is a line of code that; when the lift pb is pressed and if the hoist is at a certain position (using .acc bit from hoist position counter)it will reset both the up and down-timers.

[/quote]Since I see no physical outputs being used, I'm guessing this is just monitoring the system?[/quote]

That's correct, this is but a small part of a subroutine which is part of a much larger program.



-Eric[/quote]

 

[Eric Nelson]

I don't know what you mean by a "debounce" input.

Since you have inputs named 'ls', you might be using mechanical limit switches. The contacts in these can 'bounce', or close, open, close a few times before finally settling in the closed position. If the PLC input is faster than the bounce time, it may see these as individual pulses. To 'debounce' simply means to ignore these intermittent breaks. A very short time delay is usually enough. Most PLCs have filters on the inputs to solve this. They are adjustable on your MicroLogix (I think the default is 8ms).

I only bring this up because you are using the 'ls' input to increment/decrement your counter. If you occasionally receive multiple signals when the limit switch activates, you would see erroneous counts.



-Eric

 

[ceilingwalker]

Since you have inputs named 'ls', you might be using mechanical limit switches. The contacts in these can 'bounce', or close, open, close a few times before finally settling in the closed position. If the PLC input is faster than the bounce time, it may see these as individual pulses. To 'debounce' simply means to ignore these intermittent breaks. A very short time delay is usually enough. Most PLCs have filters on the inputs to solve this. They are adjustable on your MicroLogix (I think the default is 8ms).

I only bring this up because you are using the 'ls' input to increment/decrement your counter. If you occasionally receive multiple signals when the limit switch activates, you would see erroneous counts.



-Eric

Ohhhh, contact bounce! I am sorry, yes Iam very familiar with that. I was waiting for a high-tech instruction explanation. Thanks Eric.

 

[dcooper33]

This is O.T. but it was bugging me. When you want to quote something in your message, don't use [*/quote] on both ends of the text you want to quote. Only use that command at the end. To quote something do:
[*quote] my quote here[*/quote] (* added for illustration purposes only.
See,

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vs
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