PLC Pulsating timer

Question

I'm trying to create alternating outputs on my PLC (Mistubishi Melsec Q00UJCPU) in structured text. out1 and out2 - are outputs. IN1 - input.

Here's the code

IF IN1=TRUE THEN;
    timer1(IN:= TRUE, PT:=T#0s , Q:=timer1.Q);
END_IF;
IF timer1.Q THEN;
    out1:=FALSE;
    out2:=TRUE;
    timer1(IN:=FALSE, PT:=T#1s);
    timer2(IN:= TRUE, PT:=T#500ms , Q:=timer2.Q);
END_IF;
IF timer2.Q THEN;
    out2:=FALSE;
    out1:=TRUE;
    timer2(IN:=FALSE, PT:=T#1s);
    timer1(IN:=TRUE , PT:=T#500ms , Q:=timer1.Q);
END_IF;

Same code works in Codesys, but is not working in GX Works2. What could be wrong with it? And are there so many differents in Codesys and GX Works ST programming? Thanks!

I haven't tried your program, since I use Codesys in a Beckhoff PLC, and I see a couple of things in your listing that would generate syntax errors in my compiler. Q1: Should you have semicolons after 'THEN'? Q2: Wouldn't the first IF result in timer1.Q always true? — pboedker, Jan 18 '18 at 07:31

score 1 · Accepted Answer · answered Jan 18 '18 at 13:03

Is the GX Works2 IEC61131? If so it should use the same standard as Codesys. Does the GX Works2 code compile? As pboedker said above your code is probably generating some compiler errors. Probably something like below would work better.

InstRTrig(clk:=IN1);
InstFTrig(clk:=IN1);

IF InstRTrig.Q THEN
  timer1(IN:= TRUE, PT:=T#1s , Q:=timer1.Q);
END_IF;
IF InstFTrig.Q THEN
  out1:=FALSE;
  out2:=FALSE;
  timer1(IN:=FALSE, PT:=T#1s);
  timer2(IN:= FALSE, PT:=T#500ms);
END_IF;
IF timer1.Q THEN
  out1:=FALSE;
  out2:=TRUE;
  timer1(IN:=FALSE, PT:=T#1s);
  timer2(IN:= TRUE, PT:=T#500ms);
END_IF;
IF timer2.Q THEN
 out2:=FALSE;
 out1:=TRUE;
 timer2(IN:=FALSE, PT:=T#1s);
 timer1(IN:=TRUE , PT:=T#500ms);
END_IF;

score 1 · Answer 2 · answered Apr 02 '18 at 15:58

Your code contain a lot of mistakes.

what is this Q:=timer1.Q? First, you have to use => on output variables oа ф function block, and you cannot set output Q of the timer to the same output Q of the same timer.

When you do this

IF timer2.Q THEN
 out2:=FALSE;
 out1:=TRUE;
 timer2(IN:=FALSE, PT:=T#1s);
 timer1(IN:=TRUE , PT:=T#500ms);
END_IF;

Line timer1(IN:=TRUE , PT:=T#500ms); will only work once because you turn timer2 off line before.

Here is how you can do alternating timer without even using timer with native code. Because Timers themselves written in ST.

FUNCTION_BLOCK ALTERNATOR
VAR_INPUT
    IN: BOOL;
    T1: TIME;
    T2: TIME;
END_VAR
VAR_OUTPUT
    Q1:BOOL;
    Q2:BOOL;
END_VAR
VAR
    tStart:TIME;
    tET: TIME;
    xM:BOOL;
END_VAR

    IF IN THEN
        IF NOT xM THEN
            tStart := TIME();
        END_IF

        IF NOT Q1 AND NOT Q2 THEN
            Q1 := TRUE;
        END_IF

        tET := TIME() - tStart;

        IF Q1 AND tET >= T1 THEN
            Q1 := FALSE;
            Q2 := TRUE;
            tStart := TIME();
            tET := T#0s;
        END_IF      

        IF Q2 AND tET >= T2 THEN
            Q2 := FALSE;
            Q1 := TRUE;
            tStart := TIME();
            tET := T#0s;
        END_IF

    ELSE
        Q1 := FALSE;
        Q2 := FALSE;
    END_IF
    xM := IN;
END_FUNCTION_BLOK

This is very promptly wцкшеутб am sure there is room for optimization of this code.

In the program you can use this alternation

PROGRAM PLC_PRG
VAR
    fbT: ALTERNATOR;
    xStart: BOOL;
    xOut1: BOOL;
    xOut2: BOOL;
END_VAR
    fbT(IN := xStart, T1 := T#2s, T2:= T#1s, Q1 => xOut1, Q2 => xOut2);
END_PROGRAM

PLC Pulsating timer

2 Answers2