Reed vibration frequency meter
Reed vibration frequency meter has on its scale a set of plates in the form of elastic steel tongues, each tongue having its own resonant frequency of mechanical vibrations. The resonance oscillations of the tongues are excited by the action of the alternating magnetic field of the electromagnet.
With the passage of the analyzed current through the circuit of the electromagnet, the tongue with the closest resonant frequency to the frequency of the current begins to oscillate with the greatest amplitude.The frequency of resonant oscillations of each tongue is reflected on the scale of the instrument. So the visual indication is very clear.