A device provides a 4-20 mA output corresponding to a measurement range of 0 to 63,535 units. If the loop current reads 6 mA, what is the measurement reading?

A device provides a 4-20 mA output corresponding to a measurement range of 0 to 63,535 units. If the loop current reads 6 mA, what is the measurement reading?

• A. 19060.5
• B. 15883.75
• C. 38121.0
• D. 6353.5

Answer: (A)

The signal uses a linear relationship between loop current and the measurement range. A 20 mA current corresponds to the full-scale reading, and the current increases proportionally from there. So to find the reading for any current, you take the fraction of the current relative to 20 mA and multiply by the full-scale value. For 6 mA, the fraction is 6/20 = 0.3. Multiply by the full-scale value: 0.3 × 63,535 = 19,060.5 units. This is why the given answer uses 6 mA as 30% of full scale. Note: some conventions subtract a 4 mA baseline (treating 4 mA as zero), which would give a different result: (6−4)/(16) × 63,535 ≈ 7,941.875. The difference comes from whether you treat 0 mA or 4 mA as the zero reference.

The signal uses a linear relationship between loop current and the measurement range. A 20 mA current corresponds to the full-scale reading, and the current increases proportionally from there. So to find the reading for any current, you take the fraction of the current relative to 20 mA and multiply by the full-scale value.

For 6 mA, the fraction is 6/20 = 0.3. Multiply by the full-scale value: 0.3 × 63,535 = 19,060.5 units. This is why the given answer uses 6 mA as 30% of full scale.

Note: some conventions subtract a 4 mA baseline (treating 4 mA as zero), which would give a different result: (6−4)/(16) × 63,535 ≈ 7,941.875. The difference comes from whether you treat 0 mA or 4 mA as the zero reference.