Pulse Width Modulator (PWM)

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Short description

The Pulse Width Modulator (PWM) instruction modulates the analog input value Ax to a pulsed digital output signal. The pulse width is proportional to the analog value Ax.

 

Connection

Description

Input Ax

Analog signal to be modulated to a pulsed digital output signal.

Parameter

A: Gain
Range of values: +- 10.00

B: Zero offset
Range of values: +- 10,000

PT: Periodic time over which the digital output is modulated

p: Number of decimals
Range of values: 0, 1, 2, 3

Output Q

Q is set or reset for the proporition of each time period according to the proportion of the standardized value Ax to the analog value range.

 

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0BA1- 0BA5: The PWM function block did not exist prior to 0BA6.

 

Parameter PT

The periodic time PT can be provided by the actual value of another already-programmed function:

Parameter p (number of decimals)

Parameter p applies only to the display of the Ax value in a message text.

Description of the function

The function reads the value of the signal at the analog input Ax.

This value is multiplied by the value of parameter A (gain). Parameter B (offset) is added to the product, as follows:

(Ax * Gain) + Offset = Actual value Ax

The function block calculates the proportion of the value Ax to the range. The block sets the digital output Q high for the same proportion of the PT (periodic time) parameter, and sets Q low for the remainder of the time period.

Examples with Timing Diagrams

The following examples show how the PWM instruction modulates a digital output signal from the analog input value:

  1. An analog value of 500 (range 0...1000) as the value for Ax must be modulated to a digital signal string. The user-defined PT (periodic time) parameter is 4 seconds. At the digital output of the PWM function the digital signal string is 2 seconds high, 2 seconds low, 2 seconds high, 2 seconds low and continues in that pattern as long as parameter "En" = high.
    image\diagramm_pwm_ex1_sn.gif

  2. An analog value of 300 (range 0...1000) as the value for Ax must be modulated to a digital signal string. The user-defined PT (periodic time) parameter is 10 seconds. At the digital output of the PWM function the digital signal string is 3 seconds high, 7 seconds low, 3 seconds high, 7 seconds low and continues in that pattern as long as parameter "En" = high.
    image\diagramm_pwm_ex2_sn.gif

Calculation rule

Q = 1, for (Ax Min) / (Max – Min) of time period PT
Q = 0,
for PT – [(Ax Min) / (Max – Min)] of time period PT.

Note: Ax in this calculation refers to the actual value Ax as calculated using the Gain and Offset. Min and Max refer to the minimum and maximum values specifed for the range.

Particular characteristics to be noted when configuring

Refer to the help on analog block parameters in the Analog value processing section.

Overview