Definition
A precision electrical test instrument used to measure the capacitance of a capacitor by comparing the unknown capacitor against known capacitance values arranged in a balanced bridge circuit. The bridge is adjusted until no current flows through the detector, at which point the unknown capacitance can be read directly from the calibrated controls.
Plain English
A test device that measures how much electrical charge a capacitor can hold by balancing it against known reference values until the circuit reads zero, then reading the answer off the dial.
Context Anchor
Seen in aircraft electrical maintenance when checking capacitors, wiring, or capacitance-type fuel quantity sensing units.
Derivation
‘Capacitance’ comes from the Latin ‘capacitas’ meaning ‘ability to hold,’ which is exactly what a capacitor does — it holds electrical charge. ‘Bridge’ describes the circuit layout, where the unknown component is placed across one arm of a four-arm circuit and balanced against the others, like a bridge spanning two sides until level.
Why Pilots Care
Incorrect capacitance readings can lead to electrical troubleshooting errors or, in capacitance-type fuel quantity systems, inaccurate fuel quantity indications.
Analogy
Think of a balance scale. You place an unknown weight on one side and add known weights to the other until both sides level out. A capacitance bridge does the same thing electrically — adjusting known values until the circuit balances, then reading off the answer.
Intuition Check
Bridge does not mean a physical structure here. It means a comparison circuit used to measure an unknown electrical value.
Example Sentence 1
The avionics technician used a capacitance bridge to verify that the suspect capacitor in the radio power supply still met its rated value.
Example Sentence 2
During pre-installation checks, the mechanic verified the new filter capacitor using a capacitance bridge to ensure it met the required rating.