UT_LINEARISE — Lookup table / curve

Converts a value using a table of points with straight lines between them. Used
for tank strapping tables (level → volume for odd shapes), non-linear sensors,
V-notch weirs and flumes, valve characteristics and pump curves.

Pins

Declare the arrays once (e.g. ARRAY[1..20] OF REAL) and fill them from your
strapping table. They can be RETAIN so an HMI can edit them; an edit takes
effect on the next scan.

How it works

• Any size and any lower bound: ARRAY[1..20], ARRAY[0..9], ARRAY[-2..2].
  Point 1 is the first element of each array, so X and Y may even start at
  different indexes.
• Points = 0 uses the whole arrays, which must then be the same length.
  Points = N uses the first N of each (both must have at least N).
• The table is checked every scan. It is not OK if an X is not bigger than
  the one before (unsorted or a duplicate), any X or Y is NaN or infinite,
  Points is negative or longer than an array, or there are no points. Then
  TableOk is FALSE and Out and OutOfRange hold their last values.
• Exactly on a point gives exactly that point's Y. Y need not increase.
• A one-point table gives its Y everywhere.
• A NaN or infinite In holds Out and OutOfRange and sets BadInput.
• The maths runs in LREAL, so tables with values near the REAL limits work.
  Extrapolating far beyond a steep end segment can still exceed the REAL range.
• Cost: one pass over the points each scan (500 points is fine).

Using it

Strapping(In := LevelM, X := LevelTable, Y := VolumeTable);
VolumeM3 := Strapping.Out;