What is the basic operating principle of a shunt-type ammeter used in aircraft electrical systems?

• A. It uses a Hall-effect sensor to compute current.
• B. It measures current by the voltage drop across a low-value resistor (shunt) and provides a proportional reading.
• C. It measures current proportional to engine RPM.
• D. It only indicates battery state.

Answer: (B)

Shunt-type ammeters work by using a small, known resistance in series with the circuit. The current flowing through the load also flows through this shunt, creating a tiny voltage drop across it. That voltage is measured and, because the shunt value is known, is proportional to the current. The instrument is calibrated to display current directly from this voltage. This method keeps the resistance very low to minimize power loss, while still giving a direct current reading. In contrast, a Hall-effect sensor uses magnetic fields to infer current, engine RPM isn’t related to electrical current in this setup, and battery state is a separate parameter not a live current measurement.