Case statement

2020-02-27T21:21:26.943000Z

yes the number can be a variable, but
when you need it variable use
While counter<endnumber do
end_while

in a CASE it is not possible to use a VAR for the cases.
constants are possible

CASE INT1 OF
INT1 is a normal Variable of the INT type (byte etc possible.
1, 5: BOOL1 := TRUE;
above 1 and 5 must be a constant
BOOL3 := FALSE;
2: BOOL2 := FALSE;
BOOL3 := TRUE;
10..20: BOOL1 := TRUE;
BOOL3:= TRUE;
ELSE
BOOL1 := NOT BOOL1;
BOOL2 := BOOL1 OR BOOL2;
END_CASE;

Case statement

2020-02-27T21:21:25.489000Z

            Good and simple but is it possible to keep no.of repeats as a variable instead of a constant.

repeat:=n;

where n can be any integer

Thanks

Case statement

2020-02-27T21:21:21.404000Z

late reply, but here's an implementation in ST with a case based state machine, only one timer is needed as its used for both on and off states.

PROGRAM POU
VAR_INPUT
   // Start the sequence
   Start: BOOL;
   // Number of repeats
   Repeats: INT := 10;
END_VAR
VAR_OUTPUT
   // Output signal
   A: BOOL;
END_VAR
VAR
   State: WORD;
   Counter: INT;
   
   Timer: TON;
END_VAR
VAR CONSTANT
   STATE_START : WORD := 0;
   STATE_ON    : WORD := 1;
   STATE_OFF   : WORD := 2;
   STATE_STOP  : WORD := 3;
END_VAR
CASE State OF
STATE_START:
   IF Start THEN
      Timer(IN:= FALSE);   
      
      Counter:= 0;
      State  := STATE_ON;
   END_IF
// Puts the signal on for 1 sec
STATE_ON:
   A:= TRUE;
   
   Timer(IN:= TRUE, PT:= T#1S);
   IF Timer.Q   THEN
      // Reset timer
      Timer(IN:= FALSE);   
      
      State  := STATE_OFF;
   END_IF
// Put the signal off for 20 sec
STATE_OFF:
   A:= FALSE;
   
   Timer(IN:= TRUE, PT:= T#20S);
   IF Timer.Q   THEN
      // Reset timer
      Timer(IN:= FALSE);   
      Counter:= Counter + 1;
      
      IF Counter < Repeats THEN
         State:= STATE_ON;
      ELSE
         State:= STATE_STOP;
      END_IF;
         
   END_IF
// Done   
STATE_STOP:
   // Wait for start signal to be removed, else the sequence will be restarted
   IF NOT Start THEN
      State:= STATE_START;
   END_IF   
   
END_CASE

Case statement

2020-02-27T21:21:19.970000Z

Thanks for the idea.

Hope fully this flow chart should be correct to some extent

Case statement

2020-02-27T21:21:15.945000Z

your sequence is still not correct.
now it is 1 second on
20 seconds off
2 seconds on because the third timer is followed by the first timer.
probably you want to wait for 20 seconds again, but this you can do by jumping one step lower.
A PLC is always looping its programs, and checks if values are true, this is to avoid a standstill somewhere in a POU and rest of machine is not controlled anymore.
you can achieve your goal with

WHILE NOT timer.Q DO
nothing:=true;
END_WHILE

Case statement

2020-02-27T21:21:14.505000Z

Shooter,

In the sequence k:k+1; is supposed to increment once,in the flow but it is incremented in no time with in the FOR loop.

Attached is the flow chart

Case statement

2020-02-27T21:21:10.480000Z

flowchart still not correct.
yes within a for loop it is possible, just check if timer is expired and then move on.
use wait for this, but the program stops now.
if you haVE MORE AS ONE PROG RUNNING THIS IS BAD PRACTICE.

Case statement

2020-02-27T21:21:09.062000Z

Hi
1).I have corrected my flow chart.
2).With out SFC is it possible in for loop using a counter
Thanks

Case statement

2020-02-27T21:21:07.639000Z

For is also possible, but when you draw a simple flowchart it is easier to make an SFC

with FOR you can do
FOR a = 1 to variable
ton1
ton2
next a

i made an SFC but it is not correct, as your flowdiagram is not correct.

Case statement

2020-02-27T21:21:03.662000Z

Hi,

1).SFC is solving the problem.

2).Any reason why cannot we use FOR loop for this kind of sequence?

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