Position3P

Position3P (FB)

FUNCTION_BLOCK Position3P

Short description

Calculation of the current position of a 3-point actuator Additionally, a reference position (limit switch) of the actuator can be captured. Typical application: Position determination for a 3-point valve actuator

Representation

Interfaces

Inputs

Name	Data type	Value range	Initial value	Function
xOutOpen	BOOL			Input - Enable - Open
xOutClose	BOOL			Input - Enable - Close
xRefPos	BOOL			Digital input for detecting the reference position (limit switch)

Outputs

Name	Data type	Value range	Initial value	Function
rPos	REAL	rMinLimit to rMaxLimit		Display of the current position in %

Setpoints / parameters

Name	Data type	Value range	Initial value	Function
iRefPosition	INT	0 - 100	0%	Reference position of the actuator
rMinLimit	REAL		0.0	Limit - Minimum position
rMaxLimit	REAL		100.0	Limit - Maximum position
tDuration	TIME		T#120s	Runtime of the actuator

Function description

General

This function block is used to calculate the current position of a 3-point actuator that has no position feedback. The calculation is performed based on the duration of the signals at the inputs Input - Enable - Open xOutOpen and Input - Enable - Close xOutClose. Any rising edge on the digital input xRefPos (i.e. the actuator is currently in its reference position) triggers a redefinition of the analog output signal rPos to the target value / parameter iRefPosition.

Reference position

The digital input xRefPos allows a readjustment of the position display rPos to a predefined value iRefPosition (0% = rest position - 100% = maximum position). Any rising edge on the digital input triggers a readjustment.

Position display rPos

It is used to display the current position of the 3-point actuator in the range rMinLimit to rMaxLimit and is calculated internally. Signals at the input xOutOpen increase the value of the position display, signals at the input xOutClose decrease the value of the position display.

Limitations / Notes

The 3-point actuator must move linearly, i.e. produce the same position changes in equal time intervals. A position change via any manual override hardware that may exist will not be registered. To avoid deviations between the calculated and the actual position, regular triggering of the position display readjustment is recommended.

CODESYS

InOut:

Scope	Name	Type	Initial
Input	xOutOpen	BOOL
Input	xOutClose	BOOL
Input	xRefPos	BOOL
Input Const	iRefPosition	INT	0
Input Const	rMinLimit	REAL	0.0
Input Const	rMaxLimit	REAL	100.0
Input Const	tDuration	TIME	TIME#2m0s0ms
Output	rPos	REAL