TwoPoint

TwoPoint (FB)

FUNCTION_BLOCK TwoPoint

Short description

Linear conversion of a numerical input value using a characteristic curve defined by two points.

Representation

Interfaces

Inputs

Name	Data type	Value range	Initial value	Function
rIn_X	REAL		0	Analog value input

Outputs

Name	Data type	Value range	Initial value	Function
rOut_Y	REAL			Analog value output
xErr	BOOL			* FALSE: Conversion error-free * TRUE: Error during the conversion process

Setpoints / parameters

Name	Data type	Value range	Initial value	Function
iMinMaxOffset	INTEGER		0	Values of the limits at the analog value output rOut_Y
xMinMaxLimit	BOOL		FALSE	Enable / disable the limit at the analog value output rOut_Y
rY2	REAL		100	Point 2 of the output characteristic curve
rX2	REAL		100	Point 2 of the input range
rY1	REAL		0	Point 1 of the output characteristic curve
rX1	REAL		0	Point 1 of the input range

Function description

Analog value output rOut_Y

The analog value output rOut_Y is determined by the analog value input rIn_X depending on the linear characteristic curve defined by the two points P1(rX1/rY1) and P2(rX2/rY2) is calculated. In the event of a conversion error ( xErr = TRUE ) the analog value output rOut_Y remains unchanged.

Formula

rOut_Y = (((rX1-rIn_X)*(rY2-rY1))/(rX1-rX2))+rY1

Constraints

The analog value output rOut_Y is of data type REAL. With an inappropriate selection of the parameters rX1, rX2, rY1 and rY2 as well as the value of the analog value input rIn_X it can lead to exceeding the limits of the data type.

Enable / disable limits xMinMaxLimit

The limits of the analog value output rOut_Y can generally be enabled and disabled with this setpoint / parameter.

xMinMaxLimit	Limits	Notes
FALSE	none	rOut_Y without absolute limits
TRUE	Y_min and Y_max	Limit of the analog value output rOut_Y active

Values of the limits iMinMaxOffset

The limits of the analog value output are only active if the setpoint / parameter xMinMaxLimit is active (= TRUE). The limit values Y_min and Y_max are then calculated as follows:

Formulas:

Y_min = rY1 - ((ABS(rY2-rY1))*iMinMaxOffset)/100 Y_max = rY2 + ((ABS(rY2-rY1))*iMinMaxOffset)/100\

rY1	rY2	rY2 - rY1	iMinMaxOffset	Y_min	Y_max	Notes
0	100	100	0	0	100	Default limits
0	100	100	10	-10	110	Positive offset
0	100	100	-10	10	90	Negative offset

Digital output xErr

The digital output xErr signals an error during the conversion process. The following errors are considered:

• rX1 AND rX2 = 0

• rX1 = rX2

• rY1 AND rY2 = 0

• rY1 = rY2

Error during the conversion process	xErr	Notes
FALSE	FALSE	Conversion error-free
TRUE	TRUE	Error during the conversion process

Legend: X = any

CODESYS

InOut:

Scope	Name	Type	Initial
Input	rIn_X	REAL	0
Output	rOut_Y	REAL
Output	xErr	BOOL
Input Const	iMinMaxOffset	INT	0
Input Const	xMinMaxLimit	BOOL	FALSE
Input Const	rY2	REAL	100
Input Const	rX2	REAL	100
Input Const	rY1	REAL	0
Input Const	rX1	REAL	0