Flow Ctrl Tech Engineering

Analog Signal Scaling in PLCs: 4-20mA Current Loops, Raw Counts & Linear Interpolation

Step-by-step mathematical guide to scaling raw 12-bit/16-bit analog input values into real-world engineering units (bar, °C, m³/h, pH) in Siemens, Rockwell, and Schneider PLCs.

  • A 4mA live zero enables immediate detection of broken cables (reading drops below 3.6mA).
  • Siemens S7 analog cards scale 4-20mA to 0–27648 integer counts, whereas Rockwell cards vary by module configuration.
  • Linear scaling formula: EU = ((Raw - RawMin) / (RawMax - RawMin)) * (EUMax - EUMin) + EUMin.

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