Capacitive liquid level sensor
First Claim
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1. 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, andcomparator 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.
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Abstract
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.
96 Citations
15 Claims
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1. In a capacitive liquid level sensor for determine the liquid level of a sample in a liquid pipetting system, having:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of sensing the liquid level of a liquid sample using a probe, having a capacitance, for withdrawing the liquid from the sample, comprising the steps of:
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applying a high frequency electrical signal to the probe from a signal source, the phase or amplitude of the frequency signal being affected by the capacitance of the probe. detecting changes in the phase or amplitude of the high frequency signal, determining when the detected changes exceed an amplitude or value corresponding to the probe reaching the liquid level of the sample, and varying the frequency of the high frequency signal from the signal source in a repetitive manner at a predetermined sweep frequency, whereby interference from external radio transmitters is reduced and radiation from the source at any given frequency is reduced. - View Dependent Claims (13, 14, 15)
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Specification