What is the standard output current for most process transmitters?

• A. 4-20 mA
• B. 0-10 mA
• C. 1-5 mA
• D. 0-20 mA

Answer: (A)

The standard output signal for most process transmitters is a 4–20 mA current loop. This setup sends a current rather than a voltage, which makes the signal robust over long cable runs and varying loads. The transmitter controls the current so the receiver measures the signal by the voltage drop across a known resistor.

Why this range matters: 4 mA is the minimum calibrated signal, and 20 mA is full-scale. Having a lower limit above zero provides a live-zero, meaning a valid measurement at the low end is distinguishable from a complete fault. If the loop could sit at 0 mA for zero or for a fault, you wouldn’t be able to tell a true zero from a broken loop. The 4–20 mA span also gives headroom for faults, voltage drop, and long distances, while keeping the signal compatible with standard input modules.