Definition
An electrical measuring circuit, typically a Wheatstone bridge, arranged as four resistive arms with a sensitive galvanometer or null detector connecting the two midpoints. The bridge is said to be balanced when the ratio of resistances in one pair of arms equals the ratio in the other pair, producing zero voltage difference across the detector and zero current through it. Balanced bridge circuits are widely used in aircraft instruments and test equipment to measure resistance, temperature, strain, and position by sensing small changes that unbalance the circuit.
Plain English
A four-resistor circuit set up so that, when the resistances are in the right proportion, no current flows through the meter in the middle. Once balanced, any small change in one of the resistors shows up clearly on the meter, which is how the circuit measures things like temperature or pressure.
Context Anchor
Seen in aircraft electrical and instrument system discussions, especially where a sensor circuit compares one electrical value against another.
Derivation
From 'balance,' meaning two sides in equilibrium, and 'bridge,' the electrical term for a circuit that links two parallel branches with a detector across the middle — like a footbridge spanning a gap. When the two sides carry matching ratios of resistance, the bridge is in balance and the detector reads zero.
Why Pilots Care
A balanced bridge ensures the cockpit gauges accurately reflect fuel levels or temperatures, which is critical for safe flight planning and engine monitoring.
Analogy
Think of a seesaw with weights on both sides. When the weights are matched in the right proportion, the seesaw sits level and a marble in the middle stays still. Add or remove weight on one side and the marble rolls — that movement is what the instrument measures.
Intuition Check
Do not read balanced bridge as a physical bridge that is level or stable. Here, balanced means the two electrical comparison points are equal, and bridge means a specific circuit layout.
Example Sentence 1
The cylinder head temperature gauge uses a balanced bridge circuit, so when the sensor's resistance changes with engine heat, the bridge becomes unbalanced and the needle moves.
Example Sentence 2
Technicians adjust the circuit until the bridge balances at the calibration point during instrument checkout.