What kind of power does a 4-20mA use?

What kind of power does a 4-20mA use?

• A. DC
• B. AC
• C. Pulsating DC
• D. Three-phase DC

Answer: (A)

The signaling power used for a 4-20 mA loop is Direct Current (DC). In this setup, a DC source powers the transmitter, which modulates the current between 4 mA and 20 mA to represent the measured value. Because the signal is a current loop, the information travels as a steady current over the loop, and the receiver interprets the current level rather than the voltage. Using DC makes the loop insensitive to long cable runs and voltage drops, and it allows two-wire transmitters to be powered from the same wires that carry the signal. AC or pulsating DC isn’t used for this kind of signaling because they introduce ripple and timing issues that complicate accurate interpretation of the current as a measurement. Three-phase DC isn’t a standard concept for this purpose. So the power type for a 4-20 mA loop is DC.

The signaling power used for a 4-20 mA loop is Direct Current (DC). In this setup, a DC source powers the transmitter, which modulates the current between 4 mA and 20 mA to represent the measured value. Because the signal is a current loop, the information travels as a steady current over the loop, and the receiver interprets the current level rather than the voltage. Using DC makes the loop insensitive to long cable runs and voltage drops, and it allows two-wire transmitters to be powered from the same wires that carry the signal.

AC or pulsating DC isn’t used for this kind of signaling because they introduce ripple and timing issues that complicate accurate interpretation of the current as a measurement. Three-phase DC isn’t a standard concept for this purpose. So the power type for a 4-20 mA loop is DC.