Signals and sensors

4–20 mA loop voltage and headroom calculator

Add up the transmitter minimum voltage, receiver and cable drops and any other series drops at a design current, and compare the total with the supply.

Calculate

Supply and transmitter
V DC
V
mA
Use the maximum normal or fault current relevant to the design.
Series burden
Ω
Ω
Ω
V

Worked example

Loop voltage headroom

8.1 V

Supply required at the design current
15.9 V
Drop across the entered series resistance
5.4 V
Total entered series resistance
270 Ω
Maximum total resistance before zero headroom
675 Ω

The entered DC budget has headroom; verify every device drop, maximum component voltage and the required design margin.

Method and assumptions

Formula

headroom = supply − transmitter minimum − I × total series resistance − fixed drops

Use the complete outbound-and-return cable resistance and the transmitter minimum terminal voltage from its current datasheet.

Limits of this result

  • Use the transmitter-specific minimum terminal voltage over its operating range and fault behavior.
  • Barriers, isolators, indicators, surge protection and input resistors must all be included in the entered loop.
  • This DC budget does not assess intrinsic-safety entity parameters, grounding, EMC or hazardous-area compliance.

Technical sources

  1. 4–20 mA current-loop fundamentals, system design and setupNI · accessed 2026-09-14

Put the value to work

Read the related engineering guidance, or carry this task into System Builder to identify the signal path and EpiSensor products.

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