Vibrating rod is a single element tunned mechanical element-type level sensing device.
Electronics of LSV-R excites the piezo-electric-crystals inside tuning rod, which makes the rod vibrate at it's natural resonance frequency in free air.
When material touches the rod, vibration stops as resonance gets disturbed.
Amplitudes of vibration are above threshold when rod is free to vibrate.
Amplitudes of vibration, as seen by the electronics fall below the threshold, Material presence is thus detected by observing the amplitude of vibration.