US 3810146 A
An alarm system for the safety of non-swimmers comprises a portable transmitter which is adapted to be attached to the body of the non-swimmer and to be activated on immersion in water, and a receiver adapted to operate an alarm on receiving the transmitted signal. The transmitted signal is a mechanical wave having a frequency which is ultrasonic.
Description (OCR text may contain errors)
United States Patent 1 1 3,810,146
Lieb May 7, 1974 ALARM SYSTEM FOR THE SAFETY OF NON-SWHMMERS  References Cited  Inventor: Solomon Nathan Lieb, UNI D STATES PATENTS Johannesburg, South Africa 3,273,138 9/1966 Kolm 340/261  Assignee: Manfred Dworcan, Johannesburg, I
South Africa; a part interest Primary Exammer-John W. Caldwell Assistant ExaminerGlen R. Swann, III Filedi 13, 1972 Attorney, Agent, or FirmEric H. Waters  App]. No.: 314,839
 ABSTRACT An alarm system for the safety of non-swimmers com- 30 F A l t P t D t 1 Drag pp "on y a a prises a portable transmitter which is adapted to be Mar. 22, 1972 South A rlca 72/1956 attached to the y of the nomswimmer and to be activated on immersion in water, and a receiver  Cl 340/ 24 243 adapted to operate an alarm on receiving the transmit- 51 I t Cl Gosh 21/00 2 ted signal. The transmitted signal is a mechanical wave l C having a frequency which is ultrasonic.  Field of Search 340/261, 279, 235, 283,
340/416, 42]; 9/313 13 Claims, 5 Drawing Figures WM MAM saw/3W FIELD OF THE INVENTION FIG. is the alarm circuit.
DETAILED DESCRIPTION FIG. 1 shows the alarm system comprising a transmit- This invention relates to an alarm system for the 5 ter 10, a sensor 12, a tuned amplifier 14, an alarm cirsafety of non swimmers exposed to open water.
BACKGROUND An open body of water such as a swimming pool represents a danger to small children who cannot swim, and is a source of constant anxiety to parents of such children.
Unprotected swimming pools have been the cause of many small children loosing their lives, and with the rapid increase in the number of privately owned pools it has become necessary for some local authorities to legislate for the compulsory provision of protective fencing around such pools.
SUMMARY OF THE INVENTION It is an object of this invention to provide an alarm system to indicate entry of a child entering into a body of water.
It is a further object of the invention to provide a method of detecting the entry of a non-swimmer into the water of a swimming pool.
An alarm system for the safety of non swimmers according to the invention comprises a portable transmitter adapted to be attached to the body of a nonswimmer, means on the transmitter to actuate the transmitter on immersion in a body of water, a sensor adapted to be immersed in the body of water and further adapted to sense the output of the transmitter when actuated and, means to amplify the sensed signal and operate an alarm located out of the body of water.
Preferably the actuating means on the transmitter comprises two exposed electrodes on the transmitter adapted to be electrically bridged by the electrical conductivity of the water. The output stage of the transmitter may suitably consist of an electromechanical trans ducer capable of producing ultrasonic mechanical waves. Similarly the sensor may be a transducer capable of converting the sensed signal from the transmitter into an electrical signal which is then fed to the amplifying means to drive the alarm. The transmitted signal is preferably of a specific frequency and the amplifying means is adapted to respond only to signals of that frequency. Further according to the invention the system is included in a swimming pool.
Further according to the invention there is provided a method of detecting the entry ofa non-swimmer into a swimming pool which consists in the steps of generating an underwater signal in the pool on immersion of the non-swimmer in the pool water, detecting the signal at a fixed underwater point in the pool, and adapting the signal to operate an alarm outside the pool.
BRIEF DESCRIPTION OF THE DRAWING The invention will now be described with reference to the drawings in which:
FIG. I is a diagramatic view illustrating the components of the system,
FIG. 2 is a perspective view of the transmitter housing,
FIG. 3 is a circuit diagram of the transmitter,
FIG. 4 is the amplifier circuit, and
cuit 16 and a loudspeaker 18.
The transmitter circuit which is seen in FIG. 3 includes a replaceable mercury battery 20, two spaced electrodes 22 and 24, a switching transistor 26, a modified tuned collector oscillator consisting of transistor 28 and a tuned circuit 30, and a barium-titanate electro-mechanical transducer 32.
The transmitter circuit is encapsulated in a small waterproof button shaped housing 34, see FIG. 2, made from epoxy resin. The electrode 22 is in the form of an exposed metal disc attached to one face of the housing and the electrode 24 is similarly exposed on the opposite side of the housing. The electrode 24 is in contact with the positive terminal of the battery 20 and forms the cover of the compartment in which the battery is housed.
The housing 34 of the transmitter includes a loop 35 to which a suitable chain orthe like is attached to enable the transmitter to be securely attached to the clothing or body of a non-swimmer.
When the transmitter is not immersed in water, the base of the transistor 26 is floating and the transistor is biased to cut-off, there is consequently no base bias on the transistor 28 and the transmitter 10 is inoperative. If the transmitter is immersed in water, the electrical conductivity of the water bridges the exposed electrodes 22 and 24 and a path is formed from the positive terminal of the battery to the base of transistor 26 thereby switching it to supply a base bias to transistor 28. The oscillator circuit 30 is slug tuned to oscillate at 65 Kc/s and to produce a signal of approximately 20 volts peak to peak across the transducer 32. The transducer which is encased in the epoxy resin of the housing 34 will vibrate at the oscillator frequency. The vibration will be transmitted through the housing and create mechanical waves in the water having a frequency corresponding to that of the oscillator.
The sensor 12 (FIG. 4) is a barium-titanate electromechanical transducer. This transducer is also encapsulated in epoxy resin for waterproofing. The sensor 12 is connected by means of a co-axial cable 36 to the tuned amplifier 14.
The tuned amplifier 14 includes three transistors 38, 40 and 42 which make up a conventional three stage amplifier, transistors 44 and 46 which are collector tuned to 65 Kc/s, a further amplifier transistor 50, two transistors 52 and 54 connected as a Darlington pair and a relay 56.
The amplifier stage comprising transistors 38, 40 and 42 is adapted to be over-driven to provide a limited signal at the collector of transistor 42 when only background noise is picked up by the sensor 12. When an input signal having a frequency of 65 Kc/s is picked up by the sensor 12, the signal at the collector of transistor 42 is accepted by the tuned circuits of transistors 44 and 46 and a signal is developed across a sensitivity control 48. This signal is further amplified by transistor 50 and fed to the transistors 52 and 54 to operate the relay 56 which energizes the alarm operating circuit 16.
The alarm operating circuit 16 (FIG. 5), though shown seperately in FIG. 1, is built into the same case as the amplifier circuit 14, and consists basically of a uni-junction transistor 58 which modulates an astable multi-vibrator oscillator consisting of transistors 60 and 62 directly coupled to an output stage consisting of transistors 64, 66 and 68 which drive the loudspeaker 18. As mentioned above. when the relay 56 of the amplifier circuit closes, the alarm circuit is energized. The oscillator circuit of the transistor 58 will now function and is adapted to oscillate at about four cycles per second and produce a saw-tooth wave form. Base currents for transistors 60 and 62 are likewise varied and consequently the frequency of oscillation of the multivibrator is also varied. This varied signal is then fed to the output stage of the circuit to drive the loudspeaker 18. The alarm produced by this circuit is distinctive and is unlikely to be confused with other alarms.
In use, referring again to FlG. l, the sensor 12 is partially embedded in the wall of a swimming pool 72 below the waterlevel. The co-axial cable 36 connects the sensor to a unit 74 which houses both the amplifier and alarm circuits 14 and 16 and is in turn connected to the loudspeaker 18. The unit 74 and the loudspeaker are situated away from the pool 72. The transmitter is attached to the body of a non-swimmer 76.
The unit 74 is continuously in the on condition and when the person 76 enters the water of the pool 72 the transmitter 10 will be actuated as described above and transmit mechanical waves having a frequency of 65 Kc/s throughout the area of the pool within the confines of the water. This signal will be picked up by the sensor 12 and operate the alarm as described above.
To ensure positive functioning of the system a test circuit could be included in the circuitry of the transmitter l0 and the unit 74.
The invention is not limited to the precise constructional details as herein described. The unit 74 could for example be water-proof and located in the water or wall of the pool, alternately the sensor 12 need not be embedded in the wall of the pool and could. for example, be suspended in the water from the side of the pool by the co-axial cable 36.
1. An alarm system for the safety of non-swimmers comprising a portable transmitter adapted to be attached to the body of a non-swimmer. means on the transmitter to actuate the transmitter on immersion in a body of water, a sensor adapted to be immersed in the body of water and further adapted to sense the output of the transmitter when actuated, and means to amplify the sensed signal and operate an alarm located out of the body of water.
2. An alarm system as claimed in claim 1 in which the actuating means on the transmitter comprises two electrodes which are adapted to be electrically bridged by the electrical conductivity of the water.
3. An alarm system as claimed in claim 2 in which the electrodes are exposed to the water.
4. An alarm system as claimed in claim 2 in which the transmitter has an output stage in the form of an electro-mechanical transducer.
5. An alarm system as claimed in claim 4 in which the output frequency of the transducer is ultrasonic.
6. An alarm system as claimed in claim 5 in which the frequency is in the range 50 7O Kc/s.
7. An alarm system as claimed in claim 1 in which the sensor comprises an electro-mechanical transducer.
8. An alarm system as claimed in claim 6 in which the amplifying means is frequency-selective.
9. An alarm system as claimed in claim 1 in which the alarm comprises a loudspeaker.
10. A swimming pool alarm system for the safety of non-swimmers comprising a portable transmitter adapted to be attached to the body of the nonswimmer, means on the transmitter to actuate the transmitter on immersion in the swimming pool water, a sensor situated below the surface of the swimming pool water and adapted to sense the output of the transmitter when actuated, means connected to the sensor and adapted to amplify the sensed signal and an alarm situated out of the swimming pool water connected to the amplifying means and adapted to be operated by the amplifying means in response to the sensed signal.
11. A swimming pool alarm system as claimed in claim 10 in which the transmitter actuating means comprises two electrodes on the transmitter which are adapted to be electrically connected by the conductivity of the swimming pool water.
12. A swimming pool alarm system as claimed in claim 10 in which the transmitter output stage comprises an electromechanical transducer adapted to vibrate at a predetermined ultrasonic frequency.
13. A swimming pool alarm system as claimed in claim 10 in which the amplifier is tuned to receive only the frequency of the signal transmitted by the transmitter.