Sample program 4 (generate LookUp table)

Download TwinCAT 3 project: Program link

Program description / function:

Inclusion of LookUp table interpolation values from a terminal input signal to a field variable (and optional subsequent transfer of the LookUp table interpolation values via CoE access to the terminal using sample program 3).

It is envisaged to use a ramp generator with a trigger input, whose level, in conjunction with an input of a digital input terminal (e.g., EL1002) sets the variable "bStartRecord" to TRUE via a link (e.g., push button connected to +24 V). This allows recording of the values to be synchronized with the ramp input voltage. Alternatively, an output terminal can be used (e.g., EL2002), whose output controls the trigger input and whose output is then set to TRUE via the TwinCAT development environment ("bStartRecord" would then have to be declared as AT%Q* and linked to a terminal output).

Variable declaration sample program 4

// Variable declaration for example program 4

PROGRAM MAIN

VAR CONSTANT

   nEndX                         : BYTE := 50; // Number of support values

END_VAR

VAR

   nPAISampleIn            AT%I* : DINT; // PDO PAISamples

   bStartRecord            AT%I* : BOOL; // +Electrical junction to trigger ramp

   bGetMinMax                    : BOOL := FALSE;

   bRecordLUT                    : BOOL := FALSE;

   r_trigStartRecord             : R_TRIG;

   nX                            : BYTE := 0;

   aValues                       : ARRAY[0..nEndX-1] OF DINT;

   nYstepValue                   : DINT;

   tp_timer                      : TP;

   ton_timer                     : TON;

   nMinValue                     : DINT := 7812500;

   nMaxValue                     : DINT := -7812500;

   nYvalue                       : DINT;

   tRepeatTimerValue             : TIME := T#51MS;

   aLUT                          : ARRAY[0..99] OF DINT;

END_VAR

Execution part:

// Example program 4:

// ################# Recording of 50 sample points: #################

// a) Determination of min./max. values (corresponding to the value range of the sensor)

tp_timer(IN:=bGetMinMax, PT:=T#2.51S); // Periodic duration of ramp (+reserve)

IF tp_timer.Q THEN

   nMinValue := MIN(nPAISampleIn, nMinValue);

   nMaxValue := MAX(nPAISampleIn, nMaxValue);

END_IF

// b) Recording of values: Start

r_trigStartRecord(CLK:=bStartRecord);

IF r_trigStartRecord.Q THEN

   nX := 0;

   memset(ADR(aLUT), 0 , 100);

   bRecordLUT := TRUE;

END_IF

ton_timer();

IF bRecordLUT OR ton_timer.Q THEN

   bRecordLUT := FALSE;

   ton_timer(IN:=FALSE);

   IF(nX < nEndX) THEN

      // b.1) Record of values:

      aValues[nX] := nPAISampleIn;

      nX := nX + 1;

      ton_timer(IN:=TRUE, PT:=tRepeatTimerValue); // T=2.5s/49 = 51ms

   ELSE

      // b.2) Recording end:

      // Create linearized values:

      nYstepValue := (nMaxValue - nMinValue) / nEndX; // Y steps

      nYvalue := aValues[0];  // Common start value of the LUT

      FOR nX:=0 TO nEndX DO

         // Create LUT (X = actual values, Y = target values):

         aLUT[nX*2] := aValues[nX]; // X value

         aLUT[nX*2+1] := nYvalue;   // Y value

         // next Y value of the LUT (make a "straight"):

         nYvalue := nYvalue + nYstepValue; // f(x) = b+x

        END_FOR

   END_IF

END_IF