Pulse width modulation signal

Pulse width modulation signal

Block name

B87_PULSE_WIDTH_MODULATION

ST call

PROGRAM TEST_B87
   VAR
 BOOL1,BOOL2 : BOOL;
 REAL1 :REAL;
    TIME1 : TIME;    
   FB: LIB.CORE.V1_0.B87_PULSE_WIDTH_MODULATION;
   END_VAR
 FB(IN:= REAL1, ENABLED:= BOOL1,T:=T#10S,MIN:=0,MAX:=100,OUT=>BOOL2,TRES=>TIME1);
END_PROGRAM

Library

LIB\CORE

Version

V1.0

Description

The block generates PWM (pulse width modulation) signal with variable duty time according to the input signal.

Inputs

Input	Type	Description	Default value
IN	REAL	Input value	0
ENABLE	BOOL	Generator enable (true = running)	True
T	TIME	Signal period	15m
MIN	REAL	Value for duty time = 0 %	0
MAX	REAL	Value for duty time = 100 %	100

Outputs

Output	Type	Description
OUT	BOOL	PWM output
OUTN	BOOL	PWM output negated
TRES	TIME	Remaining time to the end of the period

Function

he block generates PWM (pulse width modulation) signal. The analogue input In is converted to binary pulsing signal with period of t. The input signal value is proportionally converted (for min ⇐ In ⇐ max). If In ⇐ min then out = false, if In >= max then out=true permanently.

The output outn is a negated value of out. The block also provides remaining time to the end of the current period tres.

The input enable sets out=false and tres=0, if set to False.

Function in case of wrong setting

If in is hidden or min > max or min ⇐ 0 then out= false.

Application example

The block is used as a signal generator for thermic valve actuators or electric heating bodies controlled by solid state relays. It is preferred to use dedicated I/O modules (Domat M312, M313). Do not use mechanical relays to control the power circuits as the number of switching cycles may be too high for mechanical relays.

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