초록

A capacitance liquid level sensor uses an oscillator and sweeps the oscillator frequency at an ultrasonic rate thereby spreading the frequency spectrum and reducing interference from external radio transmitters and interference to local radio receivers.

대표청구항 ▼

In a capacitive liquid level sensor for determine the liquid level of a sample in a liquid pipetting system, having: a pipette probe for withdrawing liquid from a sample, an oscillator coupled to the probe for applying a high frequency signal to the probe, the amplitude and/or phase of the signal be

In a capacitive liquid level sensor for determine the liquid level of a sample in a liquid pipetting system, having: a pipette probe for withdrawing liquid from a sample, an oscillator coupled to the probe for applying a high frequency signal to the probe, the amplitude and/or phase of the signal being affected by the capacitance of the probe, and comparator means for generating a level sensor signal according to the amplitude or phase of the high frequency signal for signaling the probe\s reaching the liquid level of the sample, the improvement comprising: sweep means for varying the frequency of the oscillator in a repetitive manner, at a predetermined sweep frequency whereby interference from external radio transmitter and interference to local radio receivers is reduced.