Definition
An instrument used to measure the frequency of an alternating current (AC) electrical supply by displaying which of a row of small metal reeds vibrates most strongly when exposed to the AC signal. Each reed is tuned to a specific frequency, so the one that resonates indicates the frequency of the supply being measured.
Plain English
A small device that shows the frequency of an AC electrical system by which tiny metal strip inside it shakes the most. Each strip is tuned to shake at a certain frequency, so whichever one is buzzing tells you the frequency of the power.
Context Anchor
Seen in aircraft electrical system checks, especially on older equipment where AC generator frequency is read directly from the meter.
Derivation
A 'reed' here borrows from musical instruments, where a thin strip of material vibrates at a specific pitch. The meter works the same way: each metal reed is tuned to vibrate at one frequency, and the one that 'sings' tells you what the supply frequency is.
Why Pilots Care
Aircraft AC systems must run at a precise frequency for instruments, radios, and motors to operate correctly and safely.
Analogy
Think of a row of guitar strings, each tuned to a different note. Strum near them with one specific tone, and only the matching string vibrates strongly. The reed meter does the same with electrical frequency instead of sound.
Intuition Check
Do not read “reed” as a plant here. In this term, a reed is a thin metal strip inside the meter that vibrates when the electrical frequency matches it.
Example Sentence 1
After bringing the AC generator online, the crew checked the vibrating-reed frequency meter and saw the 400 Hz reed vibrating strongly, confirming the supply was at the correct frequency.
Example Sentence 2
During system checks the mechanic watched the meter to see which reed vibrated and verify stable electrical frequency.