Position3P (FB)

FUNCTION_BLOCK Position3P

Short Description

Calculation of the current position of a 3-point drive

In addition, a reference position (limit switch) of the drive can be detected.

Typical application: Determining the position on a 3-point valve drive

Portrayal

Interfaces

Inputs

Name	Datatype	Init-Value	Init-Value	Function
xOutOpen	BOOL			Input - Release - Opening
xOutClose	BOOL			Input - Release - Closing
xRefPos	BOOL			Digital input to detect the reference position (limit Switch).

Ausgänge

Name	Datatype	Init-Value	Init-Value	Function
rPos	REAL	rMinLimit bis rMaxLimit		Display of the current position in %.

Setpoints / Parameters

Name	Datatype	Init-Value	Init-Value	Function
iRefPosition	INT	0 - 100	0%	Reference position of the drive
rMinLimit	REAL		0.0	Limit value - minimum position
rMaxLimit	REAL		100.0	Limit value - maximum position
tDuration	TIME		T#120s	Operating time of the drive

Functional description

General

This function block is used to calculate the current position of a 3-point drive that has no position feedback.

The calculation is based on the duration of the signals at the inputs “Input - Release - Opening” xOutOpen and “Input - Release - Closing” xOutClose.

Every rising edge at the digital input xRefPos (i.e. the drive is currently in its reference position) results in a new definition of the

analog output signal rPos to the setpoint/parameter iRefPosition.

Reference position

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

Every rising edge at the digital input triggers a readjustment.

Position indicator rPos

It is used to show the current position of the 3-point drive in the rMinLimit to rMaxLimit range and is calculated internally. Signals at the input xOutOpen increase

the value of the position display; signals at the input *xOutClose*reduce the value of the position indicator.

Limitations/Information

The 3-point drive must move linearly, i.e. execute the same position changes within the same time segments.

A position change via a possibly existing manual override hardware is not registered.

To avoid deviations between the calculated position and the actual position, it is recommended to initiate a readjustment of the position indicator periodically.

Visualization

Information

Element	Authors	Date	Version	Note
Function	Adam Bartod	11.2017	1.0	Initial version
Programming	Adam Bartod	11.2017	1.0	Initial version
Test	Jochen Reu /	11.2017	1.0	Initial version
Documentation	Jochen Reu	11.2017	1.0	Initial version

Codesys

InOut:

Scope	Name	Type	Initial	Comment
Input	xOutOpen	BOOL		Input - Release - Opening
	xOutClose	BOOL		Input - Release - Closing
	xRefPos	BOOL		Digital signal for detecting the reference position (limit switch)
	iRefPosition	INT	0	Reference position of the drive
	rMinLimit	REAL	0.0	Limit value - minimum position
	rMaxLimit	REAL	100.0	Limit value - maximum position
	tDuration	TIME	TIME#2m0s0ms	Operating time of the drive
Output	rPos	REAL		Display of the current position in %.