What is the typical supply voltage for 4-20 mA process transmitters?

What is the typical supply voltage for 4-20 mA process transmitters?

• A. 5 V DC
• B. 24 V DC
• C. 120 V AC
• D. 240 V DC

Answer: (B)

4-20 mA transmitters are designed to be powered by a modest DC supply in the 20–30 V range, with 24 V DC as the common standard. In a current loop, the transmitter powers itself from the supply and then controls the current through the loop to represent the process variable. That means the supply must be high enough to cover the transmitter’s internal voltage drop plus the voltage drop across the external load (often a resistor used to read the current). With 24 V, there’s typically enough headroom for these drops and for long cable runs, while staying safe and economical. If the supply were only 5 V, there wouldn’t be enough voltage to drive the transmitter’s electronics and the load at 20 mA, so the loop couldn’t accurately regulate the current. On the other end, 120 V AC or 240 V DC are not needed for standard signal loops and add unnecessary safety and equipment requirements.

4-20 mA transmitters are designed to be powered by a modest DC supply in the 20–30 V range, with 24 V DC as the common standard. In a current loop, the transmitter powers itself from the supply and then controls the current through the loop to represent the process variable. That means the supply must be high enough to cover the transmitter’s internal voltage drop plus the voltage drop across the external load (often a resistor used to read the current). With 24 V, there’s typically enough headroom for these drops and for long cable runs, while staying safe and economical.

If the supply were only 5 V, there wouldn’t be enough voltage to drive the transmitter’s electronics and the load at 20 mA, so the loop couldn’t accurately regulate the current. On the other end, 120 V AC or 240 V DC are not needed for standard signal loops and add unnecessary safety and equipment requirements.