TwoPointFun

TwoPointFun (FUN)

FUNCTION TwoPointFun : REAL

Short description

Linear conversion of a numeric input value using a characteristic curve defined by two points. Typical application: scaling of raw process values

Interfaces

Inputs

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

Outputs

Name	Data type	Value range	Initial value	Function
TwoPointFun	REAL			Linear conversion of a numerical input value
xErr	BOOL			* FALSE: Conversion error-free * TRUE: Error during the conversion process

Function description

Analog value output

The analog value output is from 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 remains unchanged.

Formula

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

Constraints

The analog value output is of data type REAL. Through an unsuitable 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 can generally be enabled and disabled with this input.

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

Values of the limits iMinMaxOffset

The limits of the analog value output are only active if the input 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
Return	TwoPointFun	REAL
Input	rIn_X	REAL
Input	rX1	REAL	0
Input	rX2	REAL	100
Input	rY1	REAL	0
Input	rY2	REAL	100
Input	xMinMaxLimit	BOOL
Input	iMinMaxOffset	INT
Output	xErr	BOOL