Siemens LOGO! Series Manual page 263

Examples with Timing Diagrams
The following examples show how the PWM instruction modulates a digital output signal
from the analog input value:
Example 1
Analog input value: 500 (range 0 ...1000)
Periodic time T: 4 seconds
The digital output of the PWM function is 2 seconds high, 2 seconds low, 2 seconds high, 2
seconds low and continues in that pattern as long as parameter "En" = high.
Example 2
Analog input value: 300 (range 0 ...1000)
Periodic time T: 10 seconds
The digital output of the PWM function is 3 seconds high, 7 seconds low, 3 seconds high, 7
seconds low and continues in that pattern as long as parameter "En" = high.
Calculation rule
Q = 1, for (Ax - Min)/ (Max - Min) of time period T, when Min < Ax < Max
Q = 0, for PT - [ (Ax - Min) / (Max - Min) ] of periodic time T.
Note: Ax in this calculation refers to the actual value Ax as calculated using the Gain and
Offset.
LOGO!
Manual, 04/2011, A5E03556174-01
LOGO! functions
4.4 Special functions list - SF
263