Machine expert basic: problem with comparison

[Varri]

Hello!

Im about to pull of all my hair over this:

With this ladder i try to make a retained timer, with the possibility to reset it.

But the comparison in rung 1 keeps failing me, if tm1.p (preset timer value) is 15 min, and the tm1.v + mw130 is 10 the result is true... iv been tesing this on m221 plc. The result is that the pump stops too soon if there has been a fault or pause.

https://pasteboard.co/J5rwmXl.jpg

Thank you for any replies

 

[Varri]

Ive been testing this in simulation aswell, if the timer preset is 150 and the resut of comparison is over 100 the output is true.

 

[L D[AR2P#0.0]]

The code you posted shows the timer preset to be 999 and a time base of seconds, but you refer to 15 minutes - can you clarify



You are acessing the timer preset and value before the timer call - will this give you a problem? (I'm not familiar with this platform so cannot simulate it)

 

[Varri]

Dont worry about the 9999 timer preset, i changed language on tags and such. I want the timer to run in minutes, but ive been testing with seconds. Same results

 

[parky]

Why not use a counter and clock pulse that way you can freeze it or reset it or even increment a word on a clock pulse.

 

[drbitboy]

Is Rung 1 evaluating this:

PUMP1.P <= (PUMP1.V + %MW130)

or this

(PUMP1.P <= PUMP1.V) + %MW130

?


Not that I know if the latter is even possible

 

[Varri]

Rung 1 is comparing Pump1.p to (pump1.v + %mw130)

 

[Steve Bailey]

This is a WAG. I don't know anything about the platform you're using, but could the unit of PUMP1.P be different than that of PUMP1.V? Perhaps TON instructions in that platform operate in milliseconds while giving you the opportunity use seconds as the preset.

 

[drbitboy]

Rung 1 is comparing Pump1.p to (pump1.v + %mw130)

I apologize for not being clear, and maybe you answered what I was asking: I was not asking what you want it to do; I was asking what the PLC is actually doing.


Because the former - what you want - is irrelevant, and only the latter matters.

 

[drbitboy]

• This is a WAG. I don't know anything about the platform you're using, but could the unit of PUMP1.P be different than that of PUMP1.V? Perhaps TON instructions in that platform operate in milliseconds while giving you the opportunity use seconds as the preset.

this was going to be my second suggestion.


Try assigning the comparison instruction input parameters - Pump1.p and (Pump1.v + %mw130) - to memory variables i.e.

• %mw200 := TM1.P;
• %mw201 := TM1.V + %mw130;

and then use %mw200 and %mw201 as the input parameters to the [<] comparison, and then you can see what the instruction is actually comparing.

 

[L D[AR2P#0.0]]

I've installed SoMachine basic - I cannot enter the syntax shown in your program, what am I doing wrong?

 

[Varri]

I've installed SoMachine basic - I cannot enter the syntax shown in your program, what am I doing wrong?

Insert the comparison block in the start from the left, and draw a line to the output set coil. Also, im using machine expert 1.2, its the new name.

 

[Lare]

Hello!

Im about to pull of all my hair over this:

With this ladder i try to make a retained timer, with the possibility to reset it.

But the comparison in rung 1 keeps failing me, if tm1.p (preset timer value) is 15 min, and the tm1.v + mw130 is 10 the result is true... iv been tesing this on m221 plc. The result is that the pump stops too soon if there has been a fault or pause.

https://pasteboard.co/J5rwmXl.jpg

Thank you for any replies

You are addind %MW130 to %MW130 + timer timed value.
This should be only %MW130:=%Tx.V as otherwise you are adding pause timer from earlier pause also.


Anyway, it would be lot of easier with counter blocks. (%C) or even %MW or %MD (int or Dint) variable, which is added by 1 every second.



Stop or not start -> reset counter (with preset value)

No start and not stop, not pause, not fault -> set counter with new value



start, no stop and no pause and no fault and r_trig of %S6 or %S7 (one secend or minute)
-> count up (or down)


Then you need 2nd rung where you compare counter value or Counter D-output with start, stop etc. bits, Set and reset bit for control

 

[Varri]

I did try to move the timer parameters to memory words, same result.
The syntax i wrote in the program compares op1 to op2 + op3. The same syntax with just = works just fine.

Of course i can write up this function from scratch, also with a counter (will actually be better because it has a reset input). But i locked in on finding out why this didnt work.

Discovered that if i move the timer call to before the comparison it actually works.. Why is that?

Attached is screen of working function, chaning the numbers or rungts etc did not have any impact on the result. It was the moving of the timer block..

 

[Lare]

I did try to move the timer parameters to memory words, same result.
The syntax i wrote in the program compares op1 to op2 + op3. The same syntax with just = works just fine.

Of course i can write up this function from scratch, also with a counter (will actually be better because it has a reset input). But i locked in on finding out why this didnt work.

Discovered that if i move the timer call to before the comparison it actually works.. Why is that?

Attached is screen of working function, chaning the numbers or rungts etc did not have any impact on the result. It was the moving of the timer block..

I don't see any new attachments?


But it have to be from scan order of rungs (from top to down). On other you are saving timed value 1 scan after timer is allready stopped.