Pw - Pulse Width Modulation - Eaton easyE4 series Manual

6.1.3.6 PW - Pulse width modulation

General
easyE4 base devices provide two function blocks for pulse
width modulation PW01...PW02.
These function blocks generate a pulse train with a constant
period. The main application for PW function blocks is when
working with devices that feature transistor outputs.
However, PW function blocks can also be used with devices
featuring relay outputs. Due to the relay's ON and OFF times, a
long period duration and a long minimum ON duration are both
possible with these devices.
Function block PW is used, among other things, to set up PID
controllers with a pulse output for proportional actuators.
When doing this, the PW function block is used together with
the DC (PID controller) function block.
Operating principle
The PW function block modulates the pulse duty factor of a square wave signal, and
thus changes the mark to space ratio and pulse duration.
The period duration of the signal stays constant.
You define the period duration at the PD input. The on time or pulse duration is pro-
portional to the manipulated variable at the SV input. You can also define the minimum
on duration at the ME input.
A hardware output is assigned to each function block:
PW01 -> Q01, PW02 -> Q02
The function block causes the direct output of the calculated value at the hardware out-
put.
If you use a PW function block with its permanently assigned
Q1 or Q2 output, you cannot make any additional associations
of these outputs in the program.
A status change at Q1 or Q2 that is caused by the circuit dia-
gram is suppressed in favor of the higher priority status
change caused by the function block.
DANGER
UNFORESEEABLE SWITCHING STATES AT OUTPUT
When using the PW function block, strictly observe the separate
assignment of the outputs if other hardware-dependent function blocks
are used, such as the PO function block.
easyE4 11/18 MN050009 EN www.eaton.com
6. Function blocks
6.1 Manufacturer function blocks
267