Applies To:
  • CitectSCADA 1.x, 2.x, 3.x, 4.x, 5.x, 6.x, 7.x

Question: How does Citect scale trend variables when an expression is used in the trend? 


With 2-byte trends, Citect scales the result of a trend expression from engineering units to generic units (0-32000) and stores this generic value in the trend files. When the trend data is displayed, the reverse scaling, (namely generic to engineering scaling) is employed. If a trend expression is a primitive variable tag, then Citect will use the engineering scales of that variable tag when converting the trend data between engineering and generic units. If the trend expression involves more than one variable tag, the engineering scales of the last variable in the expression are the scales used for the entire expression. If no tag name is used in the expression, an engineering range of 0-32000 will be used.

Citect 5.31 and later have the option of storing an 8-byte floating point value for each sample. This allows for 15 significant digits, so even LONG tags and REAL tags can be recorded without losing precision. The actual value is recorded in the data files without being scaled.