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PLC PWM help needed!!

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Tamasco

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plc pwm

Hi,
could someone help me on how to accomplish Pulse Width Modulation using siemens PLC and STEP 7 (or Omron's PLCs).

Your help will be very much appreciated. Thanks in advance.

Tamasco.
 

Siniša

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pwm plc

I am not very familiar with S7 or Omron, but in general PWM with standard output modules can be achieved only on low frequency. Limiting factor is output module and/or CPU speed. PID On-Off temperature control is using PWM to control output to heaters. There are specialized modules available either from PLC manufacturer or 3rd party module manufacturer that can perform much faster. Frequency of PWM has to be significantly faster from desired output frequency so it does not affect control process after filtration.
In temperature control for example, in 1s or 10s PWM period temeprature usually does not change significantly and thermal inertia of object whose temperature is controlled is acting as filter to PWM signal. If object thermal inertia is too low, designer has to choose faster responding system, like SCR phase control, or even using DC power for some specialized applications.
If motor control or something similar is desired, specialized modules will perform much faster without much additional loading to PLC CPU.
If you post more detail, someone might be able to suggest you most straightforward solution.
There are a lot of specialized forums on the net for PLC's, they can be even more of help.
 

    Tamasco

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Tamasco

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pwm z plc

thanks a lot!!
 

cubeusk

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plc pmw

You can make a PWM without any special module. You can do it with the timers of the automaton.Yo can use something like this:

A I 1.0
AN T 2
L S5T#10ms
SD T 1
A T 1
= Q 4.0
A T 1
L S5T#5ms
SD T 2

To change the values use the times defined with S5T#.
 

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