The timer doesn't work when it is triggured

michonezol · Feb 22, 2020

Hi everyone, I am a newbie in PLC programming.

This is my code written in ST
--------------------------------------
PROGRAM MAIN
VAR
Motor :BOOL;
Start :BOOL;

Delay :TON;

button :R_TRIG;

END_VAR
--------------------------------------
button(CLK:= Start);
Delay(IN := button.Q, PT := T#5S, Q => Motor);
--------------------------------------

The idea is simple. After 5 seconds the button is pressed, the motor will work.

But, the program doesn't work as expected. I don't understand why

Could you help me out please?

Thanks so much.

Aabeck · Feb 22, 2020

Not sure of the platform, but -

If Start is TRUE but the next line shows In FALSE it may be the syntax of Button in the 2 lines

First line = button(CLK... on the second = button.Q, maybe it is looking at a different value.

cardosocea · Feb 22, 2020

TON timers usually require the signal to be high... not be a pulse.

Perhaps if you have a pulse in the button you latch a bit that will keep the timer counting?

Lare · Feb 22, 2020

Welcome to forum

It is lot of easier start with ladder or function blocks programming than ST.

On program is couple issues.

TP (Timer pulse) makes pulse to ouput as soon there rising edge on input. it won't delay output. (pulse 5s now)

you have rising edge detection of button. Q is on "1" only one program cycle, so you can't see it on animation view.

What you need now, is TON timer

So you probaly have now 5s pulse on timer output as soon as you pressed button

p.s Forgot, there is TON timer configured on program, looked first that there is TP

You only need to configure button without R_trig

Lare · Feb 22, 2020

Aabeck said:
Not sure of the platform, but -

If Start is TRUE but the next line shows In FALSE it may be the syntax of Button in the 2 lines

First line = button(CLK... on the second = button.Q, maybe it is looking at a different value.

There is R_trig on button configured
Codesys

drbitboy · Feb 22, 2020

michonezol said:
But, the program doesn't work as expected.
[...]
Could you help me out please?

The source of the timer IN (run?) bit is a one-shot that is True/1 for exactly and only one scan, so the timer resets on the next scan.

TL;DR

button is an R_TRIG i.e. a rising edge trigger (one-shot), so button.Q will be True/1 for one scan and then reset to False/0 on the second, next scan.

I don't know what brand of PLC you are using, but I think that for most brands, Delay:TON will reset when its Delay.IN, which is one-shot output button.Q, resets on that second scan after the one-shot fires.

A TON reset means the timer will

stop running
set Q to False/0
reset ET to zero.

In most cases that second scan, when the one-shot output button.Q goes False/0, will occur before the 5s timer expires.

When button.Q goes False/0, the timer will reset and never reach its 5s PT value.

Do you know the solution? Is this a homework problem?

michonezol · Feb 22, 2020

Well, I am trying to learn a PLC program, so I have created many simple problems like turning ON/OFF a lamp, blinking a lamp, or something like that... so there is no real PLC unit involved here.

A platform is Codesys.

My own current problem is: After 5 seconds (or any second) the button is pressed, the motor will work (or turn ON). As simple as that

In most cases that second scan, when the one-shot output button.Q goes False/0, will occur before the 5s timer expires.

When button.Q goes False/0, the timer will reset and never reach its 5s PT value.

Maybe you are right.
I still don't have a solution yet

michonezol · Feb 22, 2020

Lare said:
Welcome to forum

It is lot of easier start with ladder or function blocks programming than ST.

The first lesson at school, I start with ST

Lare · Feb 22, 2020

thinking that on config you need this line

button : Bool;

(same way than you have for motor)

then on st

delay (in =button, PT = t#5s, Q => motor);

And check that you haven't used same timer multiple times on program.

michonezol · Feb 22, 2020

Lare said:
thinking that on config you need this line

button : Bool;

(same way than you have for motor)

then on st

delay (in =button, PT = t#5s, Q => motor);

And check that you haven't used same timer multiple times on program.

oh man, it works

thanks man

Lare · Feb 22, 2020

michonezol said:
oh man, it works
thanks man

Yeah, you had one shot trigger there

TON timer input was on only one program scan (which is something around 1-20ms maybe for default on your PLC configuration)
So your timer started to count, but on online you won't see it as it is so fast.

If you would have TP timer whit one shot, then it would have gived 5s pulse. (and also even with button: bool configuration)

michonezol · Feb 22, 2020

Lare said:
TON timer input was on only one program scan (which is something around 1-20ms maybe for default on your PLC configuration)
So your timer started to count, but on online you won't see it as it is so fast.

oh yeah, man, you are right. Sometimes I see the system running pretty fast, so I could not catch each step

CommissioningMan · Feb 24, 2020

You can step one cycle only, if you want to see the effect of edges.
Timers will still be iffy, though.

dorishall · Feb 26, 2020

Thanks for the great responses so far. Where can I go to find the absolute basics? Bit vs byte for an example? Or even microprocessing etc?

drbitboy · Feb 27, 2020

dorishall said:
Thanks for the great responses so far. Where can I go to find the absolute basics? Bit vs byte for an example? Or even microprocessing etc?

Google or Wikipedia should be fine for those

The timer doesn't work when it is triggured

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