help for s7-300

tulip · Feb 9, 2010

I want to write a program block that İf I input a value on screen ( between 1%-100% )plc output must like this.That is;input value is 1% than plc output must be 1% on-99% off,İf input value is 7% than plc output must be 7% on-93% off etc.( This is seems PWM ,but I dont know.)I think need two parameters for this block.First; pulse width (be % ),second is period.Is there any experience for this? Thanks in advance.

L D[AR2P#0.0] · Feb 9, 2010

Source code for FB as follows:

Code:

FUNCTION_BLOCK FB 1
TITLE =
VERSION : 0.1

VAR_INPUT
  rPerCentageOnTime : REAL ; 
  tPeriod : TIME ; 
END_VAR
VAR_OUTPUT
  bPWMQ : BOOL ; 
END_VAR
VAR
  sfb4Timer : sfb4; 
  bQ : BOOL ; 
END_VAR
BEGIN
NETWORK
TITLE =Period generator
      AN    #bQ; 
      =     L      0.0; 
      BLD   103; 
      CALL #sfb4Timer (
           IN                       := L      0.0,
           PT                       := #tPeriod,
           Q                        := #bQ);
      NOP   0; 
NETWORK
TITLE =
      L     #tPeriod; 
      DTR   ; 
      L     #rPerCentageOnTime; 
      *R    ; 
      L     1.000000e+002; 
      /R    ; 
      L     #sfb4Timer.ET; 
      DTR   ; 
      TAK   ; 
      <=R   ; 
      =     #bPWMQ; 
END_FUNCTION_BLOCK

PeterW · Feb 9, 2010

or you could use FC106 (Unscale) with the High and Low limits set to 100 and 0. The input value would need to be Floating Point though.

Manglemender · Feb 9, 2010

I think that what you want is a standard Siemens block FB43 PulsGen. You can find it in the standard library under PID control Blocks.

The code that LD provided will doubtless work but the Siemens block is a bit more clever. If you have multiple instances of FB43 it can automatically synchronise the time periods with a PID controller to even out power demand from whatever is being controlled. I've used this on multiple heating controllers so that they don't all switch on at the same time causing a spike in current demand.

Nick

help for s7-300

tulip

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L D[AR2P#0.0]

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PeterW

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Manglemender

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