If a device has a measurement range of 0-1000 units and the loop current reads 9 mA in a 4-20 mA loop, what is the measurement reading?

If a device has a measurement range of 0-1000 units and the loop current reads 9 mA in a 4-20 mA loop, what is the measurement reading?

• A. 450
• B. 225
• C. 900
• D. 100

Answer: (A)

In this setup the reading is found by scaling the loop current to the measurement range. If we treat the full-scale current as 20 mA mapping to the full-scale reading of 1000 units, then the reading is proportional to current: (9 mA / 20 mA) × 1000 = 450 units. Note: in a strict 4-20 mA interpretation, 4 mA would map to 0 and 20 mA to 1000, giving a different result for 9 mA (about 312.5 units). The given answer uses the simpler direct ratio to full-scale.

In this setup the reading is found by scaling the loop current to the measurement range. If we treat the full-scale current as 20 mA mapping to the full-scale reading of 1000 units, then the reading is proportional to current: (9 mA / 20 mA) × 1000 = 450 units.

Note: in a strict 4-20 mA interpretation, 4 mA would map to 0 and 20 mA to 1000, giving a different result for 9 mA (about 312.5 units). The given answer uses the simpler direct ratio to full-scale.