Starting/stopping TON timer

Hello everyone,

Is it possible to stop a TON timer using the same input that you used to start the timer with?

PLC used s7 1200
Software TIA v13

An IEC TON timer only has the one input "IN", which starts the timer when on and resets the timer when off.

Do you need a timer to retain the value it has "timed" when you remove the signal?

If so TON is the wrong function to use.

JesperMP said:

An IEC TON timer only has the one input "IN", which starts the timer when on and resets the timer when off.

Click to expand...

Yes I know that but is it possible to use I0.0 to start the timer and I0.1 to stop OR if I get 2 straight signals on I0.0?

Rob... said:

Do you need a timer to retain the value it has "timed" when you remove the signal?

If so TON is the wrong function to use.

Click to expand...

Not really the answer I was looking for but you can retain the value of a timer by moving the elapsed time into a variable isn't that correct?

With a little bit of code and a couple of other memory bits. You could have that one physical input doing whatever you like.

Jozir said:

Not really the answer I was looking for but you can retain the value of a timer by moving the elapsed time into a variable isn't that correct?

Click to expand...

You could do, but long winded when there's inbuilt re tentative timers.

Break down exactly what you are trying to achieve as I'm not sure I understand what you're trying to do.

Just latch a bit with i0.0 and unlatch with i0.1, that bit is your TON.IN

EDIT: Use TONR if you need to accumulate, TON if you don't.

KISS

use this instruction ---( TONR )---: Time accumulator

Rob... said:

You could do, but long winded when there's inbuilt re tentative timers.

Break down exactly what you are trying to achieve as I'm not sure I understand what you're trying to do.

Click to expand...

I need a speed measurement for a foosball tabel. I've got one sensor 20cm infront of the goal and one sensor in the goal. ( already have correct speed measurement but no direction detection)

Start timer when first sensor crossed.
Stop timer when 2nd sensor crossed.

BUT when the ball bounces next to the goal, 1st sensor gets crossed 2 times in a row and timer will still be running -> result: speed measurement wrong.

I have to prevent this :
https://ibb.co/gz07f8

I currently set the time with sensor field 1 and reset timer with sensor goal 1 or sensor field 2.

Jozir said:

I need a speed measurement for a foosball tabel. I've got one sensor 20cm infront of the goal and one sensor in the goal. ( already have correct speed measurement but no direction detection)

Start timer when first sensor crossed.
Stop timer when 2nd sensor crossed.

BUT when the ball bounces next to the goal, 1st sensor gets crossed 2 times in a row and timer will still be running -> result: speed measurement wrong.

I have to prevent this :
https://ibb.co/gz07f8

I currently set the time with sensor field 1 and reset timer with sensor goal 1 or sensor field 2.

Click to expand...

Are you trying to restart the timer in the same scan you stop it? If so, I think you can call the TON instruction twice, with the same instance data block each time. The first time you give IN a false, the second time you give it a true. That way the block sees a rising edge and resets itself.

Split the task down.

The first part, you need something that holds when the first input operates and releases when the second one operates. You can do this with a bit either M memory or a bit from a word on DB memory, you can Set and Reset the bit, or create a self-holding circuit that opens when the second input operates. You also need to have it reverse proofed so that if input 2 operates first then it ignores the input 1, again by using a latching system.

Once you have that bit sorted then you can look at the timer. A TON timer looses its value when you remove the enable signal, so if you use a TON timer you will have to grab the elapsed time before you loose the enable signal. If you use a TONR timer then the time will be held when you loose the enable signal, but you will have to reset the timer at some point. You could reset manually through another input or timeout, or you could use a rising edge (P_TRIG) to reset the timer when the first input operates.

The problem you have using standard inputs is that you limited by how quickly the PLC will see that the input has changed which involves the cycle time of the PLC which will be low milliseconds. The other limit is that standard timers have a minimum resolution in milliseconds.

mk42 said:

Are you trying to restart the timer in the same scan you stop it? If so, I think you can call the TON instruction twice, with the same instance data block each time. The first time you give IN a false, the second time you give it a true. That way the block sees a rising edge and resets itself.

Click to expand...

You mean this? : https://ibb.co/khHp2y

This looks pretty weird

BryanG said:

Once you have that bit sorted then you can look at the timer. A TON timer looses its value when you remove the enable signal, so if you use a TON timer you will have to grab the elapsed time before you loose the enable signal. If you use a TONR timer then the time will be held when you loose the enable signal, but you will have to reset the timer at some point. You could reset manually through another input or timeout, or you could use a rising edge (P_TRIG) to reset the timer when the first input operates.
.

Click to expand...

I understand what you're saying here and I already solved the problem with the ET dropping when you lose the enable signal by moving the elapsed time in a variable using a move block.

My question remains is it possible to reset that timer when I get 2 straight signals on the input that sets the timer? Like I show in my picture, I know this is wrong but there must be a way, right?

https://ibb.co/mQOU2y

Jozir said:

You mean this? : https://ibb.co/khHp2y

This looks pretty weird

Click to expand...

Agreed, definitely looks weird. I can't recall if I've done it with a timer before or not, but I know I've done it with motion instructions, communication instructions, etc. I'd recommend testing to ensure it doesn't somehow double count, just to be sure. If it ends up working for you, I'd strongly recommend some comments in your code to explain what you're trying to do there.

I'm not 100% sure on the conditions pointing to the IN, but I think that's the right idea. It makes sense when conditions will be such that the first call will be false, ending the last timer and the 2nd call will be true, starting the timer again, immediately.