FB_PWDutyOutput

Description

The PulseWhen the step gets activated, the action is activated for a single execution, and possibly once again when the step is deactivated Width Duty Cycle function block accepts an input value between the minimum and maximum input range and converts this to a duty cycle percentage. The output is then cycled on and off over the period of the duty cycle at the duty cycle percentage.

• If it is desired to have the output ON time range from 0 to the duty cycle period, the minimum should be set to zero and the maximum to the duty cycle period.
• If the calculated duty cycle based on the input and range values is less than the minimum ON time (MinTime), the output will not come on.
• If the calculated duty cycle is between or equal to the range values the output is cycled by the duty cycle.
• If the calculated duty cycle is greater than the maximum ON time (MaxTime) the output will remain on.

The following figure shows the function block I/O

Figure 8-225: Pulse Width Duty Cycle

Arguments

Input

uEN01	Description	Enable for the block
	Data type	BOOL
	Range	[0 , 1]
	Unit	N/A
	Default	—
uInputCommand	Description	Signal Input (sometimes the output of a PID"Proportional-Integral-Derivative" A PID controller is a generic control-loop feedback mechanism widely used in industrial control systems. An "error" occurs when an event or a disturbance triggers off a change in the process variable. A PID controller attempts to correct the error between a measured process variable and a desired setpoint by calculating and then outputting a corrective action that can adjust the process accordingly block).
	Data type	REAL
	Range	[0 to -- ]
	Unit	N/A
	Default	—
uPeriod	Description	Period of the duty cycle
	Data type	TIME
	Range	[0 , -- ]
	Unit	N/A
	Default	—
uMaxInput	Description	uInputCommand at or above this number that sets DutyOutput =1
	Data type	REAL
	Range	uMinInput to --
	Unit	N/A
	Default	—
uMinInput	Description	uInputCommand at or below this number set DutyOutput = 0
	Data type	REAL
	Range	0 to uMaxInput
	Unit	N/A
	Default	—
uMaxTime	Description	Maximum on time for the Output
	Data type	TIME
	Range	uMinTime to uPeriod
	Unit	N/A
	Default	—
uMinTime	Description	Minimum on-time for the PW Duty Output
	Data type	TIME
	Range	0 to uMaxTime
	Unit	N/A
	Default	—

Output

OK	Description	Fucnction block is OK.
	Data type	BOOL
	Range	[0 , 1]
TM1	Description	On-time of the Output
	Data type	TIME
	Range	0 to uPeriod
DutyOutput	Description	PW signal ( switching between 0 and 1). DutyOutput is set to 0 when the function block is not active (not eabled by the first input).
	Data type	BOOL
	Range	[0 , 1]

Usage

Flash a warning light for operators.

Related Functions

Timers

Example

Function Block Calculations

IF (uInputCommand - uMinInput) < 0 then     //If Command less than MinInput turn out put off
   DutyOutput := 0;
ELSIF (uInputCommand - uMaxInput) > 0 then     //If Command greater than MaxInput turn out put on
   DutyOutput := 1;
ELSE
   DutyCycle := (uInputCommand - uMinInput)/(uMaxInput - uMinInput);     //Calculate Duty Cycle
   ONTimeFromInput := DutyCycle * any_to_REAL(uPeriod) ;     //Calculate Ontime

   IF  any_to_TIME(ONTimeFromInput)  < uMinTime then
      DutyOutput := 0;
   ELSIF any_to_TIME(ONTimeFromInput) > uMaxTime then
      DutyOutput := 1;
   ELSE
      TM1 := any_to_TIME(ONTimeFromInput) ;
      TM0 :=  uPERIOD - TM1;     //Calculate offtime
      DutyOutput := Inst_blinkA( 1 , TM0 , TM1 );     //Use BlinkA function to set PW output
   END_IF ;
END_IF ;

Structured Text

Inst_FB_PWDutyOutput( PWDuty_3_Switch, PWDuty_In3, PWDuty_3_Period, PWDuty_3_MaxInput, PWDuty_3_MinInput, PWDuty_3_MaxTime, PWDuty_3_MinTime); PWDuty_3_OK:=Inst_FB_PWDutyOutput.OK; PWDuty_3_Time:=Inst_FB_PWDutyOutput.TM1; PWDuty_3_Output:=Inst_FB_PWDutyOutput.DutyOutput;

 

Ladder Diagram

 

Function Block Diagram

 

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