Why is the o/p range for the majority of analog devices 4 to 20 mA rather than 0 to 20 mA?

Field Instrumentation
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Why most of analog o/p devices having o/p range 4 to 20 mA and not 0 to 20 mA?

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The 4-20 mA range is preferred over 0-20 mA for most analog devices in industrial settings for several practical reasons:

  1. Fault detection: A 0 mA reading clearly indicates a problem like a broken wire or power loss.
  2. Powering transmitters: The 4 mA minimum provides power for two-wire transmitters, even at minimum readings.
  3. Noise resistance: Starting at 4 mA gives better protection against electrical interference, especially over long distances.
  4. Easier calibration: The 4 mA “live zero” makes it simpler to adjust the zero point without confusing it with a fault.
  5. Better accuracy: Using 4-20 mA increases measurement resolution since the same 16 mA span represents the full range.
  6. Wide compatibility: The 4-20 mA standard is widely used, making it easier to integrate devices from different manufacturers.

These advantages make 4-20 mA loops more reliable and practical for industrial applications, which is why they’re generally chosen over 0-20 mA systems. Refer the below link for the detailed explanation

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