Function BlockFB_PWDutyOutput

Description

The PulseClosedWhen 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

UDFB PWDutyOutput

Figure 7-226: 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 PIDClosed"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

UDFB PWDutyOutput: LD example

 

Function Block Diagram

UDFB PWDutyOutput: FBD example

 

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