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Old May 28th, 2004, 10:57 AM   #1
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mattbdb is offline
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slc 500 self resetting timer?

How do I use a self resetting timer for a SLC 500? I was instructed to use a self resetting timer as an OR branch but it won't let me use a TON as an input. What am I doing wrong? Am I just using the wrong function?
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Old May 28th, 2004, 11:30 AM   #2
Allen Nelson
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Self resetting timer

T4:0/dn +------ TON ---+
-----|/|----------| Timer: T4:0 |

The timer runs as long as it is not done.
When it's done, the timer resets.
Since the timer is reset, the done bit drops out, and the cycle repeats.
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Old May 28th, 2004, 11:31 AM   #3
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When using information about a timer as a condition in a rung there is a lot of information available. There is the preset value or the current accumulated value both of which are numeric values. These are shown as T4:X.PRE and T4:X.ACC respectively (X = timer number). (This is assuming the default file (4), obviously, depending on processor, higher numbers might be used). These would typically be used in comparison instructions.

The current status of the timer is available as bit states. These are Enable (EN) which gives the status of the line which allows the timer to function, Timing (TT) which means the timer is enabled but is still approaching its timeout, and Done (DN) which means the timer is enabled and has finished its timing. If the timer is enabled either TT or DN will be on but not both. If not enabled then none of these will be on. These are shown as T4:x\EN, T4:X\TT and T4:X\DN.

Your question was a little vague but typically the DN bit of a self resetting timer is used. I assume you mean a self resetting as one which uses an XIO -]\[- of its own DN in the enable line. The DN bit will be on for one pass through the scan. (I see Allen covered this)
Controlling outputs is the PLC's way of getting its inputs to change.
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Old May 28th, 2004, 03:10 PM   #4
Ken Moore
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See attachd file for an example in RSLOGIX 500
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Old May 29th, 2004, 08:10 AM   #5
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"Thou shallst use a self-resetting timer !".

Ask the person who put this demand what he means exactly. No use trying to solve a problem or job if you are unsure about WHAT you have to do.

"Self-restting timer" could be many things:
Just a normal timer (i.e not retentive).
A cycling timer (like Allen's suggestion).
A timer with an output that is only active during one program scan.
Maybe he meant something completely different..
See my profile interests for Q&A
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