Siemens SIMATIC S7-1200 Function Manual page 514

Instructions
9.5 Polyline
Calculating the output value
If the input value at the Input parameter is below the first x-value or above the last x-value of
the utilized points, configure the preassignment of the Output parameter with the following
settings at the OutOfRangeMode tag:
● OutOfRangeMode = 0
The output value is extrapolated with the slope of the first or last two points.
If the OutOfRangeMode tag lies outside the permissible value range of 0 to 1, the default
preassignment 0 becomes effective.
● OutOfRangeMode = 1
The output value is limited to the y-value of the first or last point.
The Output parameter has a permissible value range of a REAL data type of -3.402823e+38
to 3.402823e+38. The output value at the Output parameter is checked for validity each time
the Polyline instruction is executed. If the interpolation calculation yields an invalid REAL
value, the output value is replaced with the setting at the ErrorMode tag.
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Function Manual, 03/2017, A5E35300227-AC
PID control