How do you calculate the voltage drop across a sensor loop given the supply voltage, loop current, and total loop resistance?

How do you calculate the voltage drop across a sensor loop given the supply voltage, loop current, and total loop resistance?

• A. Vdrop = V_supply × I.
• B. Vdrop = V_supply − I.
• C. Vdrop = I × R_total.
• D. Vdrop = I × R_total; ensure supply voltage minus Vdrop remains enough for device operation.

Answer: (D)

The main idea is to apply Ohm’s law to the sensor loop. The voltage drop across the loop is the current through the loop times the total loop resistance: Vdrop = I × R_total. This tells you how much of the supply voltage is consumed by the loop itself. After finding Vdrop, you must check that the remaining supply voltage (V_supply − Vdrop) is still enough for the sensor or device to operate properly. That practical check is essential in loop-powered applications. So the best option combines both steps: Vdrop = I × R_total, and then ensure the supply minus that drop leaves sufficient voltage for the device. This is why the other choices aren’t correct: multiplying V by I gives power, not voltage drop; subtracting I from V_supply has no units or relation to resistance; using only I × R_total omits the important operating-voltage check.

The main idea is to apply Ohm’s law to the sensor loop. The voltage drop across the loop is the current through the loop times the total loop resistance: Vdrop = I × R_total. This tells you how much of the supply voltage is consumed by the loop itself.

After finding Vdrop, you must check that the remaining supply voltage (V_supply − Vdrop) is still enough for the sensor or device to operate properly. That practical check is essential in loop-powered applications.

So the best option combines both steps: Vdrop = I × R_total, and then ensure the supply minus that drop leaves sufficient voltage for the device. This is why the other choices aren’t correct: multiplying V by I gives power, not voltage drop; subtracting I from V_supply has no units or relation to resistance; using only I × R_total omits the important operating-voltage check.