Liquiphant FTL31 and FTL33 liquid level switches are based on vibrating tuning fork technology. The sensors can be used in place of float switches or conductive, capacitance and optical sensors. A piezoelectric drive causes the sensor’s tuning fork to vibrate at its resonance frequency. When the tuning fork is immersed in a liquid, its frequency changes because of the change in the surrounding medium’s density. The electronics system in the switch monitors the resonance frequency and indicates whether the tuning fork is vibrating in air or is covered by liquid.