Measuring and testing – Liquid level or depth gauge
Patent
1994-05-10
1997-12-16
Cuchlinski, Jr., William A.
Measuring and testing
Liquid level or depth gauge
G01F 2328
Patent
active
056972482
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention is relates to a device for sensing the level of liquid within a container and, particularly, to a device in the form of a solid state arrangement having no moving parts and readily adaptable to deal with containers of non-uniform shape.
SUMMARY OF THE INVENTION
There are applications where it is desirable to determine liquid level as a discrete, rather than continuous, function. An example of such a case is where the final display of level is desired to be a digital readout. Certain forms of the present invention provide a device which fulfils this function by providing a plurality of independent ultrasonic transducers disposed in such a way that the presence or absence of liquid between a given transmitter element and a given receiver element can readily be detected.
The invention and preferred features thereof are defined in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic cross-sectional view of a liquid level sensor forming a first embodiment of the invention;
FIG. 2a is a cross-sectional side view of a second embodiment of sensor;
FIG. 2b is a sectional plan view of the sensor of FIG. 2a;
FIG. 3 is a graph illustrating the operation of one aspect of the sensor of FIG.2;
FIG. 4a shows a pcb track layout used in a third embodiment;
FIG. 4b is an enlarged view of part of FIG. 4a;
FIG. 4c is a cross-sectional side view of an embodiment using the pcb of FIG. 4a;
FIG. 5 illustrates a two-segment receiver of a second embodiment, the receiver having equal but opposite receiver segments;
FIG. 6 shows the ratiometric output of the receiver of FIG. 5;
FIGS. 7a and 7b illustrate a two-segment receiver similar to that of FIG. 5 but having segments defined by a non-uniform curve;
FIG. 8 shows signal strengths from the segments of the receiver of FIG. 7a;
FIG. 9 shows the ratiometric output of the receiver of FIG. 7a and
FIG. 10 illustrates one form of electronics suitable for use with the receiver of FIG. 7a.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, a sensor comprises a pair of ultrasonic transducers 10, 12 mounted at a fixed separation S on either side of a container holding liquid 14, or directly immersed in liquid. One transducer 10 forms a transmitter and comprises a plurality of independent conductive (i.e., transmitter) segments 16 each of which may be individually addressed by associated drive electronics (not shown). The other transducer 12 forms a receiver and comprises a single conductive element 18 having a sufficient geometric extent to receive ultrasonic acoustic signals generated by activation of any of the transmitter segments 16.
The device of this embodiment is used in the following manner. An electrical stimulus is applied to each transmitter segment 16 in turn. The time delay between application of the stimulus and reception of the resulting acoustic signal may be calculated or measured for the specific liquid involved, and is governed by the speed of sound in the medium and by the physical separations of the transmitter 10 and receiver 12. If a signal has not been detected by the receiver 12 within the appropriate time window, then it can be concluded that the liquid has not reached the height of the given transmitter segment.
The above description, involving a plurality of independent segments 16 for the transmitter, would be difficult and costly to realize using physically separate piezoelectric elements.
It is a preferred feature of the invention, therefore, that the most successful reduction to practice will employ a continuous piezoelectric matrix 20 with one common electrical ground connection 22, together with a plurality of segments 16. (It is not necessary for the ground electrodes for each segment 16 to be separate.)
This can be accomplished if the mechanical coupling of acoustic energy is poor between closely-spaced electrodes: i.e. if the internal damping of t
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Derwent Publications Ltd., Section EI, Week 9132 25 Sep. 1991.
K. Owada et al, A Two-Wire Ultrasonic Level Meter with Piezoelectric Polymer-Film Sensor, 1988.
Cuchlinski Jr. William A.
The Whitaker Corporation
Worth Willie Morris
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