Capacitive proximity sensors rely on a change of capacitance to alter the resonant frequency of the oscialltor circuit. However I'm unsure as to what type is generally used in industrial type sensors.

The types of oscialltor im most familiar with are LC type such as Colpitts and RC type such as Wein Bridge.

As far as im aware an RC based oscillator will alter the output signal amplitude, wheres as the LC type will alter the frequency of the output signal.

Which of these (if at all) are used more commonly in industrial type capacitive proximity sensors?