What is the default current range for a healthy transmitter in a standard 4-20 mA loop?

What is the default current range for a healthy transmitter in a standard 4-20 mA loop?

• A. 4 to 20 mA range
• B. 0 to 20 mA range
• C. 2 to 10 mA range
• D. 1 to 9 mA range

Answer: (A)

In a standard 4-20 mA loop, the current itself carries the measurement signal. A healthy transmitter uses a live-zero arrangement, meaning it always draws at least 4 mA to stay powered and to provide headroom for signaling changes, with 20 mA representing full-scale. So the default current range is 4 to 20 mA. If the current drifts below 4 mA or above 20 mA, it typically signals a fault or abnormal condition in the loop. Other ranges don’t fit the standard because they either include 0 mA (which can be indistinguishable from a dead loop) or fail to map the full measurement span reliably.

In a standard 4-20 mA loop, the current itself carries the measurement signal. A healthy transmitter uses a live-zero arrangement, meaning it always draws at least 4 mA to stay powered and to provide headroom for signaling changes, with 20 mA representing full-scale. So the default current range is 4 to 20 mA. If the current drifts below 4 mA or above 20 mA, it typically signals a fault or abnormal condition in the loop. Other ranges don’t fit the standard because they either include 0 mA (which can be indistinguishable from a dead loop) or fail to map the full measurement span reliably.