초록 ▼

A liquid level sensing system comprising a probe and a reactive element carried by the probe. The reactive element forms a portion of a tuned circuit in a voltage-controlled oscillator. The output of the voltage-controlled oscillator is compared to a fixed frequency reference signal and a frequency/

A liquid level sensing system comprising a probe and a reactive element carried by the probe. The reactive element forms a portion of a tuned circuit in a voltage-controlled oscillator. The output of the voltage-controlled oscillator is compared to a fixed frequency reference signal and a frequency/phase detector generates a signal indicative of any difference. The frequency/phase detector output is applied to the voltage-controlled oscillator to maintain the output frequency of the oscillator at the frequency of the reference signal. The output of the frequency/phase detector is also differentiated to develop a pulse when the frequency/phase detector output signal varies rapidly, indicating initial contact between the probe and the surface of a liquid held within a container.

대표청구항 ▼

A liquid level sensing apparatus comprising: a conductive sensing member; a reactive element disposed on the member; oscillator means having an output and a tuned circuit including at least a portion of the member and the reactive element, the tuned circuit controlling the frequency of the oscillato

A liquid level sensing apparatus comprising: a conductive sensing member; a reactive element disposed on the member; oscillator means having an output and a tuned circuit including at least a portion of the member and the reactive element, the tuned circuit controlling the frequency of the oscillator means output; and detecting means responsive to the output of the oscillator means for detecting the oscillator means output frequency and generating a predetermined output when the detecting means detects a shift in the oscillator means output frequency indicating contact between the member and a liquid.