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Combo
March 16th, 2005, 06:58 AM
Right,

I wanna scale a 4-20mA on a siemens plc

I have 0 to 27648 on the analogue input

so what I do is:

I Devide the input with 27648. So at 20 mA I have 1 as result.

I multiply is with a range of 16 (4 to 20mA).

After that I Add + 4 (Offset)

Then I have scales 0 to 27648 to 4-20mA

How do u guys do this?

JesperMP
March 16th, 2005, 07:02 AM
http://www.plctalk.net/qanda/showthread.php?t=6625

SimonGoldsworthy
March 16th, 2005, 07:05 AM
What you have described is the quickest way to do it. The alternative is to use FC105 (scale) block supplied by siemens and pass parameters to perform the scaling you require.

Combo
March 16th, 2005, 07:56 AM
thanks

Lancie1
March 16th, 2005, 12:36 PM
Combo,

For PLCs that do not have a SCALE function, and even sometimes if they do but I need intermediate results for use elsewhere, then I use these equations:

Slope = (Scaled Maximum - Scaled Minimum) / (Input Maximum - Input Minimum)
Offset = Scaled Minimum - (Input Minimum X Slope)
Scaled Value = (Input Value X Slope) + Offset