6. Function blocks6.1 Manufacturer function blocks6.1.3.6 PW - Pulse width modulationGeneraleasyE4 base devices provide two function blocks for pulsewidth modulation PW01…PW02.These function blocks generate a pulse train with a constantperiod. The main application for PW function blocks is whenworking with devices that feature transistor outputs.However, PW function blocks can also be used with devicesfeaturing relay outputs. Due to the relay's ON and OFF times, along period duration and a long minimum ON duration are bothpossible with these devices.Function block PW is used, among other things, to set up PIDcontrollers with a pulse output for proportional actuators.When doing this, the PW function block is used together withthe DC (PID controller) function block.Operating principleThe PW function block modulates the pulse duty factor of a square wave signal, andthus 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 minimumon duration at the ME input.A hardware output is assigned to each function block:PW01 -> Q01, PW02 -> Q02The 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 assignedQ1 or Q2 output, you cannot make any additional associationsof 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 statuschange caused by the function block.DANGERUNFORESEEABLE SWITCHING STATES AT OUTPUTWhen using the PW function block, strictly observe the separateassignment of the outputs if other hardware-dependent function blocksare used, such as the PO function block.easyE4 11/18 MN050009 EN www.eaton.com 267
