Liquid level sensor
First Claim
1. A liquid level sensor comprising, piezoelectric sensing means, an oscillator capable of assuming an oscillation state and a non-oscilating state and including a feedback path in which the piezoelectric sensing means is connected, the piezoelectric sensing means comprising first and second piezoelectric elements mounted to provide a first and a second mechanical coupling path between said first and second piezoelectric elements, the first coupling path being arranged to provide one phase of feedback signal for the oscillator and the second mechanical coupling path being arranged to provide a second feedback signal of substantially opposite phase, the second feedback signal only being present when the piezoelectric sensing element is immersed in the liquid and in which the one phase of feedback signal causes the oscillator to assume one of its two states and the addition of the substantially opposite phase of signal causes the oscillator to assume the opposite state.
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Abstract
A liquid level sensor for determining the liquid level in a container includes an oscillator having a feedback path including first and second piezoelectric elements mounted in a turning fork arrangement to provide a first mechanical coupling path between said elements across one end of the turning fork. This first coupling path provides a first feedback signal of one given phase. A second mechanical coupling path between said elements is provided only via the liquid when the liquid is present to a level sufficient to immerse the piezoelectric elements. The second coupling path, when present, provides a second feedback signal of opposite phase to the first feedback signal. The presence or absence of the second feedback signal determines the oscillation or non-oscillation condition of the oscillator.
17 Citations
13 Claims
- 1. A liquid level sensor comprising, piezoelectric sensing means, an oscillator capable of assuming an oscillation state and a non-oscilating state and including a feedback path in which the piezoelectric sensing means is connected, the piezoelectric sensing means comprising first and second piezoelectric elements mounted to provide a first and a second mechanical coupling path between said first and second piezoelectric elements, the first coupling path being arranged to provide one phase of feedback signal for the oscillator and the second mechanical coupling path being arranged to provide a second feedback signal of substantially opposite phase, the second feedback signal only being present when the piezoelectric sensing element is immersed in the liquid and in which the one phase of feedback signal causes the oscillator to assume one of its two states and the addition of the substantially opposite phase of signal causes the oscillator to assume the opposite state.
- 11. A liquid level sensor for determining the level of a liquid in a container comprising, an oscillator capable of assuming an oscillating state and a non-oscillating state and including a feedback path comprising first and second piezoelectric elements mounted to provide a first fixed mechanical coupling path therebetween and a second mechanical coupling path therebetween via the liquid in the container and variable as a function of the container liquid level, said first coupling path being arranged to supply a first feedback signal of one phase whereby the oscillator assumes one of its two states, said second mechanical coupling path providing a second feedback signal of opposite phase to the first feedback signal only when the container liquid level is above a given level sufficient to immerse the piezoelectric elements thereby to oppose the first feedback signal and cause the oscillator to assume the second of its two states.
Specification