analog scaling problems

[sparkotronic]

Hi

I'm trying to change a project in my workplace.
I need to replace an existing analog input card with an analog in/output card on a Siemens S300 PLC.

The problem is that the input signal is 4-20mA but the I/O card reads 0-20mA.

Does anyone have any idea of some code that will turn the 0-20 into 4-20 so that I can integrate it into the original program?

Thanks in advance, Colin

 

[Brian123]

Was the original card 0-20mA as well? If so, the code to scale your input should already be in place.

Brian

 

[Phill77]

Have you checked if there are any options in hardware config for the input signal?
I know that the ET200S range of current input cards that I use can be configured for +/-20 or 4-20 mA in the Parameters tab of the module properties.

Phill

 

[TConnolly]

If 4mA was 0% and 20mA was 100% then 0mA would be -20%.

 

[L D[AR2P#0.0]]

      L     PIW  100                    //input scaled 0-20ma
      ITD   
      DTR   
      L     2.764800e+004
      /R    
      L     2.000000e+001
      *R    
      L     4.000000e+000
      <=R   
      JC    zero                        //any value of 4mA or less gives zero
      -R                                //else subtract 4mA
      L     1.250000e+000               //and scale by (20/(20-4))=1.25
      *R    
      JU    op
zero: L     0.000000e+000
op:   L     2.000000e+001               //convert from 20mA
      /R    
      L     2.764800e+004               //back to input bits
      *R    
      RND   
      T     MW   100                    //value for an input scaled 4-20mA

 

[sparkotronic]

Thanks for that!
The code worked a treat.
Balance has now been restored to the panel

What would I do without the internet.....

 

[mosquitodai]

      L     PIW  100                    //input scaled 0-20ma
      ITD   
      DTR   
      L     2.764800e+004
      /R    
      L     2.000000e+001
      *R    
      L     4.000000e+000
      <=R   
      JC    zero                        //any value of 4mA or less gives zero
      -R                                //else subtract 4mA
      L     1.250000e+000               //and scale by (20/(20-4))=1.25
      *R    
      JU    op
zero: L     0.000000e+000
op:   L     2.000000e+001               //convert from 20mA
      /R    
      L     2.764800e+004               //back to input bits
      *R    
      RND   
      T     MW   100                    //value for an input scaled 4-20mA

good idea