초록 ▼

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 prob

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.

대표청구항 ▼

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 for

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.