Out3P

Out3P (FB)

FUNCTION_BLOCK Out3P

Short description

Conversion of an analog value (e.g. P-controller) into output signals for a 3-point actuator (pulse-width modulation). Additionally, a reference position (limit switch) of the actuator can be captured.

Representation

Interfaces

Inputs

Name	Data type	Value range	Initial value	Function
xEn	BOOL			Enable of the function block
rIn	REAL			Input signal
xRefPos	BOOL			Digital input for detecting the reference position (limit switch)

Outputs

Name	Data type	Value range	Initial value	Function
xOutOpen	BOOL			Output variable Plus/More for the actuator
xOutClose	BOOL			Output variable Minus/Less for the actuator
rPos	REAL	0.0 … 100.0		Analog signal for the current position

Setpoints / parameters

Name	Data type	Value range	Initial value	Function
iRefPosition	INT	0 - 100	0%	Reference position of the actuator
tImpulsClose	TIME		1s	Duration of a pulse at the Minus/Less output
tImpulsOpen	TIME		1s	Duration of a pulse at the Plus/More output
rMinLimit	REAL		-100.0	Integral value for pulse triggering at the Minus/Less output
rMaxLimit	REAL		100.0	Integral value for pulse triggering at the Plus/More output
rDuration	TIME		120s	Runtime of the actuator
tIntegration	TIME		100ms	Duration between two integration operations

Function description

General

This function block is used to convert an analog input signal rIn into the corresponding output signals xOutOpen and xOutClose in the form of pulse-width modulation. The pulse length is always constant (tImpulsClose or tImpulsOpen) while the pause between two pulses varies in length. For a current input signal rIn of 0.0 no output pulses are generated. If the current input signal is in the positive range (0.0 - +100.0) then only at the output xOutOpen pulses are generated. If the current input signal is in the negative range (0.0 - -100.0) then only at the output xOutClose pulses are generated. The enable/disable of the function block is done via the digital input xEn. 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.

Enable input xEn

If the enable input is not active (xEn = FALSE) both outputs are xOutOpen and xOutClose reset. Additionally the integral is set to 0 and the digital signal for capturing the reference position xRefPos is non-functional. With each falling edge on the enable input the output signal xOutClose is activated continuously for a duration of rDuration + 10s and at the same time the output signal xOutOpen is deactivated (= forced movement of the actuator to the rest position).

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.

Signal generation

The analog input signal rIn (control deviation of a control process, signal symmetric around zero) is integrated over the interval tIntegration over time. That means after each integration interval tIntegration the product of rIn and the tIntegration is formed and added to the current content of the integration memory. This therefore results in a step function.

Example

rIn = 100K, tIntegration = 100ms, old value of the integration memory = 500Ks, new value (after 100ms) = 510Ks. If the integration value exceeds the threshold rMaxLimit, then at the output signal xOutOpen a pulse of length tImpulsOpen is generated.

If the integration value falls below the threshold rMinLimit, then at the output signal xOutClose a pulse of length tImpulsClose is generated. After each pulse generation the integration value is reset to 0. The threshold rMaxLimit may only take values > 0.0, the threshold rMinLimit may only take values < 0.0.

Examples with different parameters

tIntegration = 100ms, rMaxLimit = 100.0, rMinLimit = -100.0: With an input signal rIn of +5.0 at the output xOutOpen a pulse with length 1s is generated every 4s. tIntegration = 100ms, rMaxLimit = 100.0, rMinLimit = -100.0: With an input signal rIn of -5.0 at the output xOutClose a pulse with length 1s is generated every 4s. tIntegration = 200ms, rMaxLimit = 100.0, rMinLimit = -100.0: With an input signal rIn of +5.0 at the output xOutOpen a pulse with length 1s is generated every 2s. tIntegration = 200ms, rMaxLimit = 100.0, rMinLimit = -100.0: With an input signal rIn of -5.0 at the output xOutClose a pulse with length 1s is generated every 2s. tIntegration = 100ms, rMaxLimit = 200.0, rMinLimit = -100.0: With an input signal rIn of +5.0 at the output xOutOpen a pulse with length 1s is generated every 8s. tIntegration = 100ms, rMaxLimit = 200.0, rMinLimit = -100.0: With an input signal rIn of -5.0 at the output xOutClose a pulse with length 1s is generated every 8s.

Position display rPos

It is used to display the current position of the 3-point actuator in the range 0 - 100% and is calculated internally (0% = rest position, 100% = maximum position). To avoid deviations between the calculated and the actual position, regular triggering of the recalibration of the position display is recommended. The position display is independent of the signal generation, i.e. if the position display reaches an end position (0% or 100%), signals are nevertheless still sent to the outputs xOutOpen or xOutClose is generated.

CODESYS

InOut:

Scope	Name	Type	Initial
Input	xEn	BOOL
Input	rIn	REAL
Input	xRefPos	BOOL
Input Const	iRefPosition	INT	0
Input Const	tImpulsClose	TIME	TIME#1s0ms
Input Const	tImpulsOpen	TIME	TIME#1s0ms
Input Const	rMinLimit	REAL	-100.0
Input Const	rMaxLimit	REAL	100.0
Input Const	tDuration	TIME	TIME#2m0s0ms
Input Const	tIntegration	TIME	TIME#100ms
Output	xOutOpen	BOOL
Output	xOutClose	BOOL
Output	rPos	REAL