Which voltage range corresponds to the standard 4-20 mA current when using a 250 Ω resistor?

Which voltage range corresponds to the standard 4-20 mA current when using a 250 Ω resistor?

• A. 0-1 V
• B. 2-4 V
• C. 5-10 V
• D. 1-5 V

Answer: (D)

The key idea is converting current to a voltage with a resistor using Ohm’s law: V = I × R. With a 250 Ω resistor, the 4 mA lower end gives V = 0.004 A × 250 Ω = 1 V, and the 20 mA upper end gives V = 0.020 A × 250 Ω = 5 V. So as the current in a 4–20 mA loop changes, the voltage across the resistor ranges from 1 V to 5 V. This is why the 1–5 V range is the correct match for a 4–20 mA signal with a 250 Ω shunt. In practice, the loop supply must be higher than 5 V to provide some overhead.

The key idea is converting current to a voltage with a resistor using Ohm’s law: V = I × R. With a 250 Ω resistor, the 4 mA lower end gives V = 0.004 A × 250 Ω = 1 V, and the 20 mA upper end gives V = 0.020 A × 250 Ω = 5 V. So as the current in a 4–20 mA loop changes, the voltage across the resistor ranges from 1 V to 5 V. This is why the 1–5 V range is the correct match for a 4–20 mA signal with a 250 Ω shunt. In practice, the loop supply must be higher than 5 V to provide some overhead.