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[padees]

Remember guy's, he's using a Pico, and no mention of an HMI, which I doubt they support.

They support timers and counters, but nothing really fancy like suggestions.

It's just considered a smart relay and not a traditional PLC, like we all know and love. LOL

Here is a link to the manual: Pico Manual

Maybe Bit can wrap his head around this.

 

[TheWaterboy]

Set up Flip Flop logic and detect the falling edge with ONSF . Contact bounce might be an issue so you will have to account for that.

 

[Operaghost]

Yeah, those are terrible! I guess they do have a place in specific situations, but I've never come across one.

LOL. I just replied to another post and commented about a Timer Off Delay. I explained it as if you want to turn something ON AFTER a period of time, use the TON and monitor the DN bit. If you want to turn something OFF AFTER a period of time, then use the TOF and monitor the DN bit.

There are times when you can use either and just swap XIC and XIO. But there are other times when that won't work. Usually due to an undesired startup state. I used to give students a real simple task and ask them to solve it. They would nearly always use a TON and could almost never solve it properly. If they used a TOF, they had it pretty easily.

The task was a projector. It has an On/Off button and two outputs. A fan and a lamp. Anytime the unit is turned on both outputs should energize. When the unit is turned off, the lamp should turn off, but the fan should run for 30 seconds. This is very easy with a TOF, but much harder for a TON.

Invariably there would be some mix of one shots and latches with a TON and usually the fan would turn on immediately when we went into run mode and then shut off after 30 seconds. After that, it would work properly, but it always energized on entering run mode. I told them it could not do that. The fan should only run when the unit is on or for the cooldown period when it turned from on to off.

OG

 

[OkiePC]

My main issue with the TOF is that the DN bit is TRUE as soon as the rung-in conditions are met and it stays true until a time delay after the TOF rung goes false which is bass-ackwards from almost everything else you will monitor in a PLC.

I avoid them when at all possible, which is more than 98% of the time.

 

[TheWaterboy]

I use TOF to run pumps for a couple more seconds after the stop signal in Sump pits. Just to pull a little more than the level probes would allow.

 

[drbitboy]

My main issue with the TOF is that the DN bit is TRUE as soon as the rung-in conditions are met and it stays true until a time delay after the TOF rung goes false which is bass-ackwards from almost everything else you will monitor in a PLC.

I avoid them when at all possible, which is more than 98% of the time.

This is so funny

The TON is a Timer ON delay, I think almost everyone can understand that, and I understand that the fact that it's output bit (/DN, .Q, etc.) is never 1 when the input rung state is True is comfortably understandable.

The TOF is a Timer OFf delay, so even from those words you can understand why it's output can be 1 when the input rung state is False, depending on the (time) history, but it still generate these strong opinions. To me it's just another tool in the toolbox, use it if it makes sense so you don't tie knots in logic trying to make a TON do what a TOF does with no extra coaxing.

Of course it's backwards, that's by design

 

[robertmee]

I use TOF to run pumps for a couple more seconds after the stop signal in Sump pits. Just to pull a little more than the level probes would allow.

Also accomplished by a TON delay of the level probe going off, as the signal to stop the pump

 

[Operaghost]

I realize we are getting way off topic, but the instructor in me can't let this go. I have seen people spend far to much time forcing a TON into an application where a TOF was designed to work. And I saw it in the confusing code at many of the customers I worked with.

Using an on-delay to delay turning something off? That in itself can be more confusing than a TOF. XIO instructions on the DN bit that triggered every time they went into run mode meant they had to write code to prevent that. Which made it all the more confusing.

There is surprisingly little difference between the TON and TOF timers if you really think about.

For a TON, when does the done bit turn on? When the rung goes true and a delay has expired.
For a TOF, when does the done bit turn on? When the rung goes true (no delay).

Now how about turning off?

For a TON, when does the done bit turn off? When the rung goes false (no delay)
For a TOF, when does the done bit turn off? When the rung goes false and a delay has expired

So for either timer, the DN turns on when the rung goes true and turns off when the rung goes false. The only difference is when does the delay come in to play.

OG