This article will show you how to create a retention timer in TwinCAT3.Actually, I received an inquiry from a social networking service asking me if I could teach TwinCAT3 how to create a retention timer, so I answered that inquiry.

Come on, let’s enjoy FA.

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Implementation1

First implement the program for the hold timer directly in the POU.

VAR

PROGRAM MAIN
VAR
xIN : BOOL;
tPT : TIME;
xPAUSE : BOOL;
　　 xQ : BOOL;
tET : TIME;

fbPause : R_TRIG;
tTimePaused : TIME;
fbton : TON;
END_VAR

Program

Here is the program.

//Reset the PT
IF NOT xIN THEN
tTimePaused := T#0s;
END_IF

//Detect the Pause
fbPause(CLK := xPAUSE);

//Keep the Time
IF fbPause.Q THEN
tTimePaused := tTimePaused + fbton.ET;
END_IF
//FB
fbton(
IN := xIN AND NOT xPAUSE
,PT := tPT – tTimePaused
,Q=>xQ
);
//Output
xQ := fbton.Q;
tET := tTimePaused + fbton.ET;

If xIN is FALSE, the timer’s recording time is reset to 0s.

R_TRIG FB is used to detect the xPAUSE start-up signal.

When xPAUSE startup is detected, the elapsed time (ET) of the current TON is added to the Buffer variable (tTimePaused).

Then call TON FB.Note that the PT (i.e., TON setting time) is

tPT (setting time) minus the time difference when xPAUSE starts up.

Result

To verify that the retention timer worked correctly, add a YT Scope project and define the appropriate Axis Group.

As shown in the figure below, when xIN (orange line) is ON, eET in TON is adding time.And when xPAUSE (green line) is TRUE, eET stops adding time.Finally, when eET=PT, xQ (blue line) is ON.

Implementation2

The next step is to convert the program created in Implementation 1 to FB.

fbRetainTimer

Add FB to the TwinCAT project.

VAR

This one defines IN/OUT/internal variables for the program you just created.

xIn: Input, TRUE = timer enabled
tPT:Input, timer set time
xPause:Input, timer pause
xQ:Output, TRUE=Timer ON

FUNCTION_BLOCK fbRetainTimer
VAR_INPUT
xIn :BOOL;
tPT :TIME;
xPause :BOOL;

END_VAR
VAR_OUTPUT
xQ :BOOL;
END_VAR
VAR
tET:TIME;
fbPause : R_TRIG;
tTimePaused : TIME;
fbton : TON;
END_VAR

Program

Here is the program, which works the same as Implementation 1.

MAIN

Finally, declare Instnace in the MAIN program and check its operation.

VAR
fbtimers:ARRAY[0..3]OF fbRetainTimer;
END_VAR

//

fbtimers[0](tPT:=T#30S);
fbtimers[1](tPT:=T#4S);
fbtimers[2](tPT:=T#5S);
fbtimers[3](tPT:=T#6S);