vibrating-reed frequency meter

vibrating-reed frequency meter

[′vī‚brād·iŋ ¦rēd ′frē·kwən·sē ‚mēd·ər]
(engineering)
A frequency meter consisting of steel reeds having different and known natural frequencies, all excited by an electromagnet carrying the alternating current whose frequency is to be measured. Also known as Frahm frequency meter; reed frequency meter; tuned-reed frequency meter.