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How to reset timer type PULSE

Engineering 🇬🇧
Edxx
2016-10-26
2016-11-07

  • Edxx - 2016-10-26

    Hi
    I'm new in the forum so Regards to All

    I have question how to reset output of the pulse timer TP.
    By the rising triger condition "A", I activate timer TP for fixed time, I wish to reset this time in case when comming another condition "B"

    I writing program for Beckhoff PLC in CFC.
    Is possible to manage this logic with SR, trigers etc by I looking for simplest reset of the timer.

    Best regards
    Ed

     

  • Anonymous - 2016-11-07

    Originally created by: scott_cunningham

    What should happen when Condition B is held high? Should the output stay ON, if it was on? What if the output was already OFF (TP expired) and you set Condition B high? Should the output stay OFF?

    You may be best to program your special need using ST as it's own FB, instead of trying to use a combination of TONs, TOFs, SRs, etc. Here is an example that assumes holding CondB high will keep timer at 0 until dropped low. Maybe CondB should be edge triggered?

    The code below seems to work, but please test it yourself. Maybe this can be handled with a CFC solution without a state machine, but I didn't try.

    FUNCTION_BLOCK TP_RST
VAR_INPUT
   IN : BOOL;
   PT : TIME;
   RST : BOOL;
END_VAR
VAR_OUTPUT
   Q : BOOL;
   ET : TIME;
END_VAR
VAR CONSTANT
   INIT : INT := 0;
   RUN_PULSE : INT := 1;
   PULSE_DONE : INT := 2;
   RESET_TIME : INT := 3;
END_VAR
VAR
   Timer : Standard.TON;
   State : INT;
END_VAR
CASE State OF
   INIT://Make sure output and timer are off
      Timer(IN:=FALSE, PT:=PT, ET=>ET);
      Q := FALSE;
      //See if user wants to start pulse
      IF IN THEN
         State := RUN_PULSE;
      END_IF
      
   RUN_PULSE://Normal pulse (output is true)
      Timer(IN:=TRUE, PT:=PT, ET=>ET);
      Q := TRUE;
      //See if timer reset requested
      IF RST THEN
         State := RESET_TIME;
      END_IF
      //See if timer expired (this overrides RST signal if timer is already done)
      IF Timer.Q THEN
         State := PULSE_DONE;
      END_IF
   
   PULSE_DONE://Pulse is done - ignore RST input
      //Keep timer TRUE to maintain ET like normal TP
      Timer(IN:=TRUE, PT:=PT, ET=>ET);
      Q := FALSE;
      //See if user shuts off timer
      IF NOT IN THEN
         State := INIT;
      END_IF
      
   RESET_TIME://User wants to extend pulse output (keep output high)
      //Reset timer (ET = 0 again)
      Timer(IN:=FALSE, PT:=PT, ET=>ET);
      Q := TRUE;
      //Watch for drop of RST - and go back to normal pulse output
      IF NOT RST THEN
         State := RUN_PULSE;
      END_IF
      
   ELSE //problem in code - reset state machine so FB doesn't freeze
      State := INIT;
      
END_CASE
     

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