4–20 mA Loop Scaling

I = 4 + 16 × (val − min) / (max − min)

Calculator

Result
—

Formula

I = 4 + 16 × (value − min) / (max − min) mA

Description

The 4-20 mA current loop is the dominant analog signaling standard in industrial process control. The process variable is linearly mapped so that 4 mA represents the minimum value and 20 mA represents the maximum. The 4 mA live zero provides several critical advantages: it powers the transmitter (two-wire loop powered), it distinguishes a valid zero reading from a broken wire (which reads 0 mA), and it provides consistent power to the transmitter regardless of signal level. The 16 mA span (4 to 20) represents 100% of the measurement range.

Variables

  • I — Loop current (mA)
  • val — Current process variable value
  • min — Process variable at 4 mA (range minimum)
  • max — Process variable at 20 mA (range maximum)

Practical Notes

NAMUR NE43 recommends that currents below 3.6 mA or above 21.0 mA indicate a fault condition. Current signals are immune to voltage drops in long cable runs (up to several km) and electrical noise, making them far more reliable than voltage signals in industrial environments. HART protocol overlays digital communication on the 4-20 mA signal without disturbing the analog reading.

Related Formulas

4–20 mA Burden Voltage Thermocouple Cold Junction Compensation Control Valve Flow (Cv) PLC Scan Time

Need more features?

Save calculations, import telemetry data, simulate battery discharge, and collaborate with your team.

Try the App