초록 ▼

From the time of power on, an output of a variable frequency generating circuit is kept matching with the resonance frequency of a resonance circuit. When an object of detection comes into contact or to the vicinity of a detection electrode and the resonance frequency of resonance circuit changes, a

From the time of power on, an output of a variable frequency generating circuit is kept matching with the resonance frequency of a resonance circuit. When an object of detection comes into contact or to the vicinity of a detection electrode and the resonance frequency of resonance circuit changes, a phase deviation is generated from the output of the variable frequency generating circuit. The deviation is detected by a phase comparing circuit, and a control circuit changes a control voltage so that the oscillation frequency of variable frequency generating circuit is changed to attain phase matching. This change is detected by a detection circuit, and presence/absence of the object is detected.

대표청구항 ▼

[ What is claimed is:] [1.]1. A capacitance type detector detecting a level of an object of detection in accordance with a capacitance of the object in a container, comprising:an electrode body inserted to said container;a resonance circuit including a capacitance formed between said electrode body

[ What is claimed is:] [1.]1. A capacitance type detector detecting a level of an object of detection in accordance with a capacitance of the object in a container, comprising:an electrode body inserted to said container;a resonance circuit including a capacitance formed between said electrode body and said object of detection, and a resonance transformer to be tuned therewith;a phase comparing circuit comparing phases of an output signal of said resonance circuit and a reference signal, and outputting a phase difference signal in accordance with the phase difference;a control circuit outputting a control signal to eliminate said phase difference, in response to said phase difference signal from said phase comparing circuit;a variable frequency generating circuit generating a frequency signal of an oscillation frequency in accordance with the control signal from said control circuit, and applying the frequency signal to said phase comparing circuit as said reference signal and to said electrode body;a reference value setting circuit setting a reference value for determining detection of said object of detection;a detection circuit comparing the control signal output from said control circuit or the frequency signal output from said variable frequency generating circuit with the reference value set by said reference value setting circuit and outputting a detection signal;an output circuit outputting a signal representing presence/absence of said object of detection in accordance with the detection signal of said detection circuit; anda phase difference determining circuit responsive to the phase difference signal output from said phase comparing circuit, determining phase difference between the resonance frequency of said resonance circuit and the oscillation frequency of said variable frequency generating circuit, and in response to determination of presence of a phase difference, operating said phase comparing circuit such that the oscillation frequency of said variable frequency generating circuit follows the resonance frequency of said resonance circuit.