Lookup table example

2020-02-27T14:07:50.562000Z

I prefer to have a struct like this:

TYPE udtSoundingTable :
STRUCT
   Level : ARRAY [0..10] OF REAL;
   Volume : ARRAY [0..10] OF REAL;
END_STRUCT
END_TYPE

As for the code, I use a modified binary search.
As parameters, I pass my level array and the actual level of the tank and the function will return the upper and lower indexes between which my value is.

FUNCTION FindClosest1D
VAR_INPUT
   key : REAL;
END_VAR
VAR_IN_OUT
   arr : ARRAY [*] OF REAL;
END_VAR
VAR_OUTPUT
   out1 : INT;
   out2 : INT;
END_VAR
VAR
   size : DINT;
   i: INT;
   j: INT;
   middle: INT;
END_VAR

//Binary search
size := UPPER_BOUND(arr,1);
IF key <= arr[0] THEN
   out1 := 0;
   out2 := 0;
   RETURN;
END_IF
IF key >= arr[size] THEN
   out1 := TO_INT(size);
   out2 := TO_INT(size);
   RETURN;
END_IF
i := 0;
j := TO_INT(size);
middle := 0;
WHILE (i < j) DO
   
   middle := (i+j)/2;
   IF key = arr[middle] THEN
       out1 := middle;
       out2 := middle;
       RETURN;
   END_IF
   
   IF key < arr[middle] THEN
      
      IF (middle > 0) AND (key > arr[middle - 1]) THEN
         
         IF key < 0 THEN
             out1 := middle - 1;
             out2 := middle;
         ELSE
             out1 := middle;
             out2 := middle - 1;
         END_IF
         RETURN;
      END_IF
      
      j := middle;
         
   ELSE
      
      IF (middle < size ) AND (key < arr[middle + 1]) THEN
          out1 := middle;
          out2 := middle + 1;
          RETURN;
      END_IF
 
      i := middle + 1;
      
   END_IF
END_WHILE

And after, I do a Linear Interpolation.

FUNCTION LinearInterpolation : REAL
VAR_INPUT
   X : REAL;
   X1 : REAL;
   Y1 : REAL;
   x2 : REAL;
   Y2 : REAL;
END_VAR
VAR
END_VAR

IF Y1 <> Y2 THEN
   LinearInterpolation := Y1 + (X - X1) * ((Y2 - Y1)/(X2 - X1));
ELSE
   LinearInterpolation := Y1;
END_IF

Bellow is an example on how I use them:

PROGRAM Prog
VAR
   Tank1: udtSoundingTable := (Level := [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10], Volume := [12.3, 15.8, 19, 21.3, 25.9, 29, 32.3, 34, 36, 38, 40]);
   ActualLevel: REAL; //Modify this
   Volume: REAL;
   x1: INT;
   x2: INT;
END_VAR

FindClosest1D(arr := Tank1.Level, key := ActualLevel, out1 => x1, out2 => x2);
Volume := LinearInterpolation(X1 := Tank1.Level[x1], X := ActualLevel, x2 := Tank1.Level[x2], Y1 := Tank1.Volume[x1], Y2 := Tank1.Volume[x2]);

Lookup table example

2020-02-27T14:07:50.195000Z

I use a level sensor to measure liquid level in a non linear tank and I need to convert the measured level in mm to volume in liters.
The look up table of the tank looks like below:

mm : lt
0 : 53
10 : 78
20 : 99
.
.
1990:13423
2000: 13478

The values in between 0-9, 10-19 etc will be calculated using linear interpolation.
Any suggestions or programing examples on how to implement the aforementioned algorithm are welcomed.

I think the values in the table should be entered into a two dimentional array and then I need to make a search for an appropriate value.

Recent posts to Lookup table example

Lookup table example

Lookup table example