In a typical 4-20 mA loop, which current value represents 100% of the device range?

In a typical 4-20 mA loop, which current value represents 100% of the device range?

• A. 20 mA
• B. 4 mA
• C. 12 mA
• D. 0 mA

Answer: (A)

In a 4-20 mA loop, the transmitter translates the measured value into a current that ranges from 4 mA to 20 mA. The 4 mA level represents 0% of the range (the minimum), while the 20 mA level represents 100% of the range (the maximum). Values in between map linearly, so 12 mA would be about halfway through the span above the 4 mA offset (calculated as (12−4)/(20−4) = 0.5, roughly 50%). A current of 0 mA would indicate a fault or break in the loop. Therefore, the current that represents 100% of the device range is 20 mA.

In a 4-20 mA loop, the transmitter translates the measured value into a current that ranges from 4 mA to 20 mA. The 4 mA level represents 0% of the range (the minimum), while the 20 mA level represents 100% of the range (the maximum). Values in between map linearly, so 12 mA would be about halfway through the span above the 4 mA offset (calculated as (12−4)/(20−4) = 0.5, roughly 50%). A current of 0 mA would indicate a fault or break in the loop. Therefore, the current that represents 100% of the device range is 20 mA.