Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1992-12-03
1996-01-09
Chilcot, Jr., Richard E.
Communications: electrical
Condition responsive indicating system
Specific condition
367908, 340618, 73290V, G08B 2100
Patent
active
054832268
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an ultrasonic detector for liquid media comprising a plate-shaped- ultrasonic transmitter and a corresponding ultrasonic receiver mounted facing each other on a common support serving to attach them at a principal face thereof and to define a space providing a linear acoustic path extending from the transmitter through the liquid to be detected to the receiver, an exciting circuit comprising a frequency generator connected to the transmitter via an amplifier and a detecting circuit comprising a rectifier with a low-pass filter, which is connected to the receiver via an amplifier and to at least one comparator with an adjustable threshold.
BACKGROUND OF THE INVENTION
The state of the art relating to ultrasonic detectors operating by acoustic transmission through the liquid to be detected may be illustrated for example by the following patent documents:
The ultrasonic detectors described in DE 31 49 909 A1, U.S. Pat. Nos. 4,787,240 and 4,063,457 notably comprise elastic elements which are inserted between the transducers and their support and thus constitute an acoustic insulation.
Another type of liquid detector may moreover be mentioned which operates by ultrasonic propagation within a solid detecting body arranged in contact with the liquid to be detected. Detectors of this type are described for example in the patent applications FR 2 617 965 A1; FR 2 628 527 A1 and EP 0 372 700 A1.
Known ultrasonic detectors such as those cited above nevertheless require a more or less complicated structure, generally do not ensure control of their operation and have important limitations with regard to their respective fields of application.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a relatively simple liquid-detector which offers complete operational security and is suitable for an extensive field of applications, notably for the control of pumps, valves and/or alarms constituting a part of control or safety systems.
To this end, the invention provides an ultrasonic detector that contains an ultrasonic transmitter and an ultrasonic receiver that are both mounted upon a common support (i.e., a support that is common to both the transmitter and receiver) and that face each other at a space therebetween, thereby providing a linear acoustic path through a liquid that is to be detected. A transmitter circuit is provided that includes a frequency generator and amplifier that is connected to the transmitter; and a receiver circuit a provided that includes a rectifier with low-pass filter, an amplifier, and a comparator having an adjustable threshold. The invention ensures automatic control of the operating state of the detector in absence as well as in presence of the liquid to be detected.
The ultrasonic transmitter of the liquid detector according to the invention is subjected to two different excitation modes in order to ensure on one hand the detection in presence of liquid and on the other hand automatic control of the operating state of the detector, while the detecting circuit periodically delivers the control signal as well as the liquid-detection signal.
The frequency generator is arranged so that it generates on one hand the axial-resonance frequency permitting to produce ultrasonic waves transmitted through the liquid to be detected, and on the other hand the radial-resonance frequency permitting to produce ultrasonic waves transmitted through the common support.
The two excitation frequencies are preferably the fundamental axial and radial resonance frequencies of the transmitter used.
Periodic control of the operating state of the detector is ensured via the common support on which the ultrasonic transmitter and the receiver are mounted so as to ensure good mechanical and acoustic connection in order to constitute a waveguide able to ensure permanent control of operation of the whole detector.
Axial excitation of the transmitter moreover produces crosstalk in the common support but does not enable adequate control of
REFERENCES:
patent: 3100885 (1963-08-01), Welkowitz et al.
patent: 3656134 (1972-04-01), Brown
patent: 4540981 (1985-09-01), Lapetina et al.
patent: 4929114 (1981-11-01), Silvermetz et al.
patent: 5192933 (1993-03-01), Rodriguez
Artis Jewel V.
Chilcot Jr. Richard E.
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