It is used to measure the applied frequency. Vibrating Reed Frequency meters indicate the supply frequency by means of individual reeds, when rated voltage ± 20% is applied across the terminals of the meter, the particular reed, whose natural frequency of vibration coincides with the supply frequency, vibrates with full amplitude. In case the supply frequency falls midway between two reeds both the reeds vibrate, at reduced amplitude. The amplitude of vibration at the tip of reeds is high enough for a distinct indication.
The instrument can be operated at 110V, 220V, or 440V. Terminal screws with washers are provided for the selected operating voltage & remaining two terminals are covered with insulated caps.
In case of RFD96 and RFD144 instruments, two sets of reeds with the same scale range can be offered, giving two independent meters in one casing. This facilitates in comparing the frequency of two voltage supplies for paralleling operation