Signalling and communicationQuestion 119 of 1506

What is the usual loop impedance of a 4-20 mA loop, as stated in the text?

  1. About 250 ohms
  2. About 2.5 ohms
  3. About 25 kilohms
  4. About 4 megohms
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Correct answer: About 250 ohms

Its low impedance helps load down small noise voltages.

Source: Lessons in Electric Circuits IV: Digital (Kuphaldt), 14.1: Introduction to Digital Communication

Practice signalling and communication

Questions last reviewed: 18 October 2026