Level sensing
First Claim
1. A level sensor for sensing the level of a flowable material, the sensor comprising:
- a single circuit for measuring capacitance;
exactly two electrodes, comprising a return electrode and a measuring probe, wherein the measuring probe comprises;
at least two, electrically-common, level-detecting formations, each of the formations arranged substantially parallel to a free surface of the flowable material, whereby two step rises in the capacitance are measurable by the circuit as the flowable material rises past first one of the formations and then the other of the formations.
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Accused Products
Abstract
A capacitance measurement circuit 1 has a pair of level indicating LEDs 2,3. Via one input 4, the circuit is connected to the metallic wall W of a container C of water. This connection can be direct or, as indicated by broken lines, via earth. Via a second input 5, the circuit is connected to a probe 6. This has a stem 7 with a transversely arranged disc 8 at its lower end. Spaced above the lower end, a second, larger, transverse disc 9 is secured to the stem. The stem and the discs are of conductive metal, typically copper, and electrically connected and common. The entire probe is insulated, except for its point of contact with the input 5.
When the liquid is just below the level of the lower disc 8, the capacitance between it and earth, the liquid being conductive, will be determined by the area of the disc, its separation from the liquid and the dielectric constant of the intervening gap. The capacitance varies in proportion to the gap. Hence when the liquid is well below the disc the capacitance will be small. As soon as the liquid covers the disc, the capacitance will reach a maximum—for this disc. The maximum will be dictated by the thickness of the insulation material separating the disc as such from the liquid and the fact that the area is in effect doubled by the liquid covering both surfaces.
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Citations
15 Claims
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1. A level sensor for sensing the level of a flowable material, the sensor comprising:
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a single circuit for measuring capacitance;
exactly two electrodes, comprising a return electrode and a measuring probe, wherein the measuring probe comprises;
at least two, electrically-common, level-detecting formations, each of the formations arranged substantially parallel to a free surface of the flowable material, whereby two step rises in the capacitance are measurable by the circuit as the flowable material rises past first one of the formations and then the other of the formations. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
means for measuring the capacitance between the pair of electrodes; and
means for outputting a first signal if the capacitance is within a certain tolerance of a first threshold and for outputting a second signal if the capacitance is within a certain tolerance of a second threshold.
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14. The level sensor of claim 13 further comprising:
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two counters and means for controlling the counters so that if neither threshold is reached;
each counter is decremented;
if just the first threshold is reached, the first counter is is incremented and the second counter is decremented; and
if both thresholds are reached both counters are incremented.
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15. The level sensor of claim 13 wherein the circuit for measuring capacitance is configured as a microchip.
Specification