초록 ▼

A sensor detects when a probe contacts liquid in a container due to a change in frequency of a probe oscillator. The sensor can have its output compared to a reference level to determine the presence or absence of liquid wherein the reference level is changed to follow the output of the detector. In

A sensor detects when a probe contacts liquid in a container due to a change in frequency of a probe oscillator. The sensor can have its output compared to a reference level to determine the presence or absence of liquid wherein the reference level is changed to follow the output of the detector. In one embodiment, it can be determined that liquid has been contacted when a count has been reached several times in a row (the count being a function of the probe output and changeable). In another embodiment of the invention, it can be determined that liquid has been contacted when a count has been reached within a certain threshold several times in a row, while still having the reference count change to follow the probe output (regardless of the threshold). A digital counter can be provided to determine the frequency of the probe oscillator. A reference counter can also be provided to tune the count (frequency) from the probe oscillator counter to thereby compensate for drift. And, the adjustable detection threshold permits control of the sensitivity by changing the parameters of the circuit.

대표청구항 ▼

[ I claim:] [1.] A liquid sensor for sensing a surface of a liquid, comprising:a probe for touching the surface of the liquid;a probe oscillator coupled to the probe, outputting a frequency signal;a probe counter outputting a cycle count as a function of counted cycles of the frequency signal output

[ I claim:] [1.] A liquid sensor for sensing a surface of a liquid, comprising:a probe for touching the surface of the liquid;a probe oscillator coupled to the probe, outputting a frequency signal;a probe counter outputting a cycle count as a function of counted cycles of the frequency signal output by the probe oscillator;a reference counter storing and outputting a reference count which represents frequency;a comparator comparing the cycle count output by the probe counter to the reference count output by the reference counter;a liquid detection counter, maintaining a third count in response to a preliminary detection signal and outputting a detection signal indicating the contact of the probe to the surface of said liquid when said third count passes a first predetermined value; anda controller, outputting at regular intervals, such thatwhen the comparator indicates the reference count is less than the cycle count, the controller increases the reference count stored in the reference counter and resets the liquid detection counter,when the comparator indicates the reference count is greater than the cycle count, the controller decreases the reference count stored in the reference counter and outputs the preliminary detection signal to the liquid detection counter, andresetting the cycle count in the probe counter.