S7lite ladder program

[valski gonzaga]

Hi guys, am a bit of a beginner, trying to learn plc programming ...in step 7 lite software, can you please give me an example of a ladder program...(analog input and analog output), thanks

 

[ivo.maenen]

Search the forum for "analog step7" or "FC105" and you can find something like:

http://www.plctalk.net/qanda/showthread.php?t=44643&highlight=fc+105

This should also work for the S7-lite software.

 

[valski gonzaga]

Hi Ivo,
Thanks for the help, but the FC105 my way of understanding is for the analog input scaling, how would I write the program to output the analog input proportionately to the say for example control valve?

 

[ivo.maenen]

The valve is your analog output. For this you can use FC106.

http://www.plctalk.net/qanda/showthread.php?t=46418&highlight=FC106


On this forum you can also find STL-code that has the same functionality as FC105/106. But that's more advanced programming.

 

[valski gonzaga]

Thank you Ivo.... Have already tested the program and it work well.(4-20mA input equals 4-20mA output), but I cannot monitor the out in FC106 (PQW256 output) in my laptop or in the HMI. I have assigned the PQW256 as an integer and it doesn't show anything unlike in the FC105 out (PIW256)-which can be monitored. Please help.
Thanks

 

[ivo.maenen]

Normally PQW 256 is not assigned to the PIQ (proces image outputs)so you can not monitor it straightforward inside a VAT.

Try this:

L PQW256
T MW 100

and look at MW100 inside a VAT.

 

[L D[AR2P#0.0]]

You cannot use the instruction L PQW256

If you want to monitor a PQW then transfer it to a MW first and then to the PQW address, you can then monitor the MW

e.g.

 

[L D[AR2P#0.0]]

I would write my own FC as a wrapper for FC106 and include an extra output for monitoring purposes:

FUNCTION FC 1106 : WORD
TITLE =
VERSION : 0.1


VAR_INPUT
  IN : REAL ;    
  HI_LIM : REAL ;    
  LO_LIM : REAL ;    
  BIPOLAR : BOOL ;    
END_VAR
VAR_OUTPUT
  OUT : INT ;    
  MONITORED_OUT : INT ;    
END_VAR
VAR_TEMP
  iData : INT ;    
END_VAR
BEGIN
NETWORK
TITLE =

      CALL fc106 (
           IN                       := #IN,
           HI_LIM                   := #HI_LIM,
           LO_LIM                   := #LO_LIM,
           BIPOLAR                  := #BIPOLAR,
           RET_VAL                  := #RET_VAL,
           OUT                      := #iData);
      L     #iData; 
      T     #OUT; 
      T     #MONITORED_OUT; 
      SET   ; 
      SAVE  ; 

END_FUNCTION

 

[ivo.maenen]

L D[AR2,P#0.0]:

Thanks, indeed you are correct for the same reasons as I wanted to point out. Only I forgot that even this is impossible to do. Show me that testing/controling is always a part of the solution.

Edit: and now it hits me: I intended to use the method in post #7.