question about latching

lets say i have a normally open push button and i want to use it to start a timer i know i need to use OTL to latch it on but im not sure what use for the output. i could latch on one of the output module's unused terminals but that just seems wrong somehow

You need to describe how you want this button to work in more detail.

When you push this button and it latches the output, is there another button to unlatch it? Does it unlatch after a few seconds? Does it unlatch as soon as you release it? Does it latch the output after a few seconds of holding the button?

xic b3:0/0 otl b3:0/1 is boring and doesn't do much once it is pressed..

there are two buttons one for latching and the other to unlatch so after the first button is pushed it stays latched until the other button is pressed

Whats the purpose of the timer?
What brand of PLC/SLC or ?? are you using?

You don't really need to use the OTL instruction here. What you want to use is a seal-in branch.

If all you need is the timer, you don't even need an output.

Your logic will consist of an XIC of your one PB in series with an XIO of your second PB (assuming this second PB is also N.O....If it is N.C. which is common in start/stop circuits, use an XIC also). The end of your rung will be the timer (TON). You'll have a branch around the XIC of the 1st PB. The condition of this branch is XIC of the Timer.EN bit.

Now, when you press the start PB, the timer starts timing and the timer.EN bit is true which 'seals' in the start pb. Even when you release the start PB, the timer is still timing because the .EN bit is still high. Once the timer completes, you can use the Timer.DN bit elsewhere in your program. It will stay on until the Stop PB is pressed. If you want this to be a one time event, then you can change the seal in from the timer.en bit to timer.tt bit so that the circuit also unseals when the timer finishes.

gah i keep forgetting things... its an allen-bradely slc 5/02. the program is to run some lights to act like traffic lights, there are 4 timers and 6 lights the timers cascade then repeat until the stop button is pressed

infwinra said:

gah i keep forgetting things... its an allen-bradely slc 5/02. the program is to run some lights to act like traffic lights, there are 4 timers and 6 lights the timers cascade then repeat until the stop button is pressed

Click to expand...

In that case you will need an output just to say that you are in the 'run timer' mode.

XIC of your start PB with the XIO of your stop PB and an OTE of a B3 bit. The seal-in around the start PB is an XIC of the same B3 bit. When the start PB is pressed, the B3 bit comes on and is sealed on with the same bit until the stop PB is hit.

Now, use XIC of the same B3 bit to start your first timer. The .DN bit of the 1st timer starts the 2nd timer. The .DN bit of the 2nd timer starts the 3rd timer. The .DN bit of the 3rd timer starts the 4th timer. The .DN bit of the fourth timer use in the 1st timer rung in series with the XIC of the B3 bit so that when the 4th timer is done, the 1st timer's rung goes false and resets the 1st timer. This will in turn reset all the timers because each .DN bit goes false and the process starts over.

thank you kind sir you have provided exactly what i was looking for

infwinra said:

gah i keep forgetting things... its an allen-bradely slc 5/02. the program is to run some lights to act like traffic lights, there are 4 timers and 6 lights the timers cascade then repeat until the stop button is pressed

Click to expand...

Ahh, yes I seem to remember when we seasoned gents directed the student to check the archives about this topic.

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