Powder sensor

Abstract

A powder sensor includes a piezoelectric element, an oscillator circuit, a first square wave signal generator, a second square wave signal generator, and a phase judgment circuit. The oscillator circuit applies to the piezoelectric element an output signal having a frequency equal to or near a resonance frequency of the piezoelectric element. The first square wave signal generator generates a first square wave signal by converting a terminal voltage of the piezoelectric element. The second square wave signal generator generates a second square wave signal that transits from an initial level to a detection level when the first square wave signal rises or falls in a detection period and that does not transit outside of the detection period. The detection period is a part of each cycle of the output signal of the oscillator circuit. The phase judgment circuit determines phase of the second square wave signal.

Dependencies are inferred from the claim text.