US2783459A - Alarm system for swimming pools - Google Patents

Description

upu- C. C. LIENAU ETAL ALARM SYSTEM FOR SWIMMING POOLS Feb. 26, 1957 Filed Sept. 21, 1953 2 Sheets-Sheet l INVENTO Rs: ('4 RA 6'. A IE/VA u ga f/ 11 ci/frrriasowfe Feb. 26, 1957 c. c. LIENAU ETAL ALARM SYSTEM FOR SWIMMING POOLS 2 Sheets-Sheet 2 Filed Sept. 21, 1953 new ATTORNEYS:

AL SYSTEM FOR SWIMMING POOLS Carl (1. Lienau, East Orange, N. L, and Joseph C. Patterson, Jr., Falls Church, Va.

Application September 21, 1953, Serial No. 381,324

Claims. (Cl. 340-458) This invention relates to warning systems for swimming pools and more particularly to a system for giving a warning signal when a body remains submerged in a swimming pool for a predetermined period sufficient to raise a question whether a person is in distressed condition.

On a number of occasions persons have been found drowned in swimming pools even though many other swimmers were in the pool at the same time and well trained life-guards were on duty. In cases of distress, resulting in a swimmer sinking to near the bottom of a pool prompt detection is necessary in order to provide the greatest chance for removing the person from the water before drowning occurs. But in the normal use of a pool undistressed swimmers are passing through various zones comprising the pool and divers are passing through zones near the deep end of the pool and close to the bottom of the pool. Also some objects of lesser size than the body of a child, such for example as bathing caps, water toys, etc. will on occasion sink to the bottom of a pool and will have an effect on signals transmitted through the water although of lesser degree than the body of a small child. It is therefore necessary that the alarm system be able to distinguish between distressed persons and non-distressed swimmers or other objects and yet give alarm quickly enough to leave time for efiectively aiding a drowning person.

It is an object of the present invention to provide a system of the above mentioned kind.

Another object of the invention is to provide a system in which signal actuating means comprise means for measuring the degree of reduction in a signal transmitted through the water, and rejecting disturbances less than a critical minimum amount coacting with means for measuring the duration of the disturbance and rejecting disturbances of less than a predetermined minimum duration.

Another object of the invention is to provide method and means by which signals from. a unitary source may be passed a plurality of times through water in a pool, and through a plurality of zones within a pool thus providing a watch over a substantial pool area with a' minimum of equipment.

Other objects of the invention will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, arrangements of parts, and in the several steps and relation and order of, each of said steps to one or more of the others thereof, all as will be pointed out in the following description, and the scope of the application of which will be indicated in the following claims.

The invention will best be understood if the following description is read in connection with the drawings, in which,

Figure 1 is an end elevational view showing means, partly diagrammatically, for creating a closed signalling circuit comprising in part water within the pool;

States Patent Figure 2 is a view similar to Figure 1 but showing a modification of the signalling means and circuit of Figure 1;

Figure 3 is a view similar to Figures 1 and 2 but showing another modification of the signalling means and circuit;

Figure 4 is a view similar to Figure 1 but showing in detail the electrical portion of the closed signalling system illustrated in Figure 1; and

Figure 5 is a schematic view showing graphically fluctuations in the system disclosed in Figures 1 and 4 resulting in reductions in the warning signal insufficient in degree or duration to actuate alarm or responder means, and other reductions in the warning system which are sufficient in degree and duration of time to actuate such alarm means.

The numeral 10 indicates a swimming pool having therein water up to the level indicated by the line 12. On one side of the swimming pool at a predetermined level above its bottom a transducer T1 is positioned and on the opposite wall of the swimming pool at substantially the same level the transducer T2 is positioned. The transducers are interconnected in an enclosed energy circuit which includes filter means F, amplifying means A, an output level control means L and the oscillator means 0. Also interconnected with the output level control L is a demodulator D and a delay network d which in turn is connected through a relay, as best seen in Figure 4, to a responder R which may be any desired type of signalling device. Electrical energy transmitted to transducer T1 is transformed thereby into sound energy which is transmitted to the opposing transducer T2 substantially along the line indicated by the numeral 14 in Figure l constituting the main transmission path. Lines 16 and 18 indicate smaller portions of energy transmitted by transducer T1 in angular directions. It will be seen that the energy travelling along line 16 escapes from the surface of the pool and is dissipated while energy travelling along line 13 is reflected at the surface of the water 12 to the transducer T2. The line 20' indicates stray energy which may be from any of a variety of possible sources, including energy from transducer T1 reflected from a point above the surface of the water.

In the embodiment of the invention illustrated in Figure 1 a warning signal is given only when energy being transmitted along the line 14 is reduced by any cause by more than a predetermined amount for more than a predetermined time interval. The critical amount of reduction in the energy transmitted along the line 14 is less than the reduction which would be caused by the presence of the body of any person including a very small child anywhere along the path between T1 and T2. The minimum time interval is determined to be more than the ineriTal of a casual visit to the bottom of the pool by an active and undistressed swimmer and less than a period determined by physiological considerations.

Figure 2 shows a smaller but somewhat modified embodiment of the invention in which the transducers T1 and T2 are both positioned on the same side of the pool and energy transmitted into the water from transducer T1 is successively reflected at the points 22, 24 and 26 before impinging on transducer T2. The remainder of the circuit may be as described in connection with Figure 1. It will be noted that transducers T1 and T2 are positioned at an angle, to direct and receive sound signals travelling along a zig-zag path, the angle being preferably great enough to insure reflection with a minimum of absorption in the reflecting surfaces.

In Figure 3 another embodiment of the invention is shown in which only one transducer T is employed which serves .both as the energy transmitting and receiving means. In this embodiment of the invention energy is transmitted across the pool and is reflected directly back to transducer T. In this embodiment of the invention the oscillator O is connected .to a circuit including filter means F, amplifier A and' output level control means L from a point 28 just beyond the output level control to a point 30 between transducer T and filter F.

The apparatus represented in the block diagrams in association with Figures 2 and 3 can be employed in association with a plurality of transmission-reception channels by the expedient of a scanning or periodic switching device, not shown. This extension to a system of multiple closed transmission-reception channels serves the end of the invention which ,is to maximize the volume of pool surveyed by a given complement of apparatus.

In Figure 4 the elements comprising the system are detailed. Any of a number of diiferent kinds of transducers may be employed including, magnetic, electrostatic diaphragm, crystal or electro-striction, and magneto-striction. Filter F may be of knownkind and is selected to pass electric wave energies of frequency spectrum characteristic of the transducer structure. A is a tuned amplifier with provision for rejecting signals of less than a predetermined amplitude. In the embodiment shown the predetermining element is resistance 32 which adjusts the grid bias voltage. Its function is to reject signal voltages which are less than the predetermined minimum required to actuate the succeeding elements of the system including particularly the demodulator and responder system. The inductance 34 and the capacitance 36 serve both as load impedance and for frequency selective purposes analogous to the filter F.

Connected across the output terminals 38 and 40 of amplifier A is an adjustable potentiometer 42 by which the desired fraction of the available output of the amplifier is passed on by leads 44 and 46 to slip ring means 48 of the demodulator D. For convenience in explanation a voltmeter V is shown connected between leads 44 and 46, readings of which, under circumstances described below, are represented by the curve V1. in Figure 5.

The contact ring means 48 is shown mounted on a rotating cam d actuated by constant speed motor M, and having the projection 52 which, once for each rotation of the cam, closes the switch 54 controlling the potential of grid 2 of the gas discharge tube 56 which, together with the condenser 58, is indicated generally as comprising the oscillator 0.

Tube 56 is of the kind containing an inert gas which is normally non-conductive but is rendered conductive when the grid 2 is given a positive potential with respect to the cathode k. Closure of the switch 54 places a high positive potential on grid 2. The tube 56 is thereby rendered conductive, effectively connecting condenser 53 from ground indicated at 60 to one terminal 62 of condenser 64, the other terminal of which is indicated by the numeral as. The circuit including transducer T1 and condensers 64 and 58 in parallel now oscillates at a frequency determined by the structure of the transducer and the condensers and thus providing signals which are transmitted to water within pool 1%.

The time of transit of the sound signal through the water is much greater than the transmission of the signal from transducer Tz to the demodulator point. The latter interval is negligible. During the interval beginning with the closure of switch 54 and ending with the arrival of the pulse signal at the output terminals of the demodulator the camturns through an angle proportionate to the time of transit of the pulse through the water in the pool from T1 to T2. The arriving pulse fires the glow discharge tube 68. Positioned in operative relation to tube 68 is the photoceil 79 which is energized by radiation from bulb 63 when thelatter is lighted. When cell '70 is energized by impinging light from bulb 68 current flows from a source of energy B+ through the resistance 72 and the photo cell 70 to ground indicated at 74. The potential drop developed across the resistor 72 charges the condenser 76. This resistor-condenser combination represents one kind of a delay network. The potential across the condenser 76 holds a relay 78 in normally open position. When glow discharge tube 68 is extinguished the Voltage across condenser 76 begins to decay and continues to decay as long as the tube remains extinguished at a time rate dependent upon the resistance and capacitance of the combination 7276. This time constant determines the period of delay in closing the relay 78. When the output voltage of the delay network falls to a predetermined critical value the normallyopen contact 80 closes thereby ctuating a responder R to give a Warning signal.

In Figure 5 curve VL represents the hypothetical readings of the voltmeter of the level indicator L. In the embodiment of the invention illustrated in Figure 4 it is desirable to use a voltmeter indicating root mean square value. In the system described in Figure 4 the pulses arrive with a repitition rateof considerable frequency in comparison with the period of the voltmeter needle and a voltmeter of the above mentioned kind is desirable to prevent vibration of the voltmeter needle. The diagram in Figure Sassumes that the system has been in operation beginning at time zero. It is assumed that the water path is clear of interruption for substantially 40 seconds represented by constant values for V1,. Under these conditions the glow discharge lamp 68 will flash at a position displaced by a constant angle from the zero point ofits rotation. This interval is described as all clear. The delay network output voltage is sufficient to hold relay contact 80 open, and accordingly the responder R is inactive.

Reductions in the intensity of the transmitted signal, as indicated by VI. in Figure 5 are of two kinds-those originated in the waterpath and those in the electrical system connecting transducers T1 and T2. A fluctuation resulting from a supply line voltage or battery voltage change is illustrated in Figure 5 beginning at 45 seconds and indicated generally by the numeral 82. If sufficient in magnitude such a variation or a circuit failure in the system will actuate the responder R. The variation indicated by numeral 82 is, however, less than the critical amount and is not suflicient to cause responder R to be actuated. The variation indicated by the numeral 84 is, however, great enough to actuate responder R if continued for a sufl'lcient interval of time. Variation 84 is not of suflicient duration to actuate R but when continued as is illustrated by the portion 36 of the curve it will result in actuation of R. Variation 84 represents the effect of a casual interruption of the sound path by the passage of an active or undistressed swimmer through the field of transmission from T1 to T2, of less duration than the minimum duration of interruption required for actuating responder R.

The curve of delay network output voltage corresponds with the hypothetical variations in the voltage of the voltage level control L, and thus only a small dip occurs at 88 corresponding with the fluctuation 82; a greater dip occurs at 90 corresponding with the substantial but momentary decrease in voltage indicated at 84; but it will be noted that thedip 92 corresponding with the prolonged decrease in voltage indicated by the numeral 86 extends down below the line indicating the critical voltage for operating the responder, this line being crossed after a-period marked Delay which represents the predetermined time interval ofiinterruption for actuating the responder. Once the alarm signal is actuated it will continue to actuate until the interfering body is removed from the field of energy transmission between T1 and T2, which in curve 86 is indicated by the return in the curve to its normal level at the point marked Recovery. Continued interruptionpf the signal transmission would result in continued actuation of the responder R as indicated by the hatched line on the right hand side of the portion of the curve marked 92.

In Figure 4 the switch s1, s2 is shown provided with a movable contact member 94 illustrating an alternative manner of triggering the pulse generator. When s1 is open and s2 is closed the grid 1 of tube 56 is connected to the output of the amplifier. The arrival of a pulse at grid 1 initiates a second pulse train of oscillations in transducer T1. A second pulse train of oscillations is initiated in the manner previously described and proceeds through the water, transducer T2, filter and amplifier to the glow tube 68. The second pulse upon arrival initiates a third pulse in the same manner through grid 1. During the interval the condenser 58 has been recharged from the energy source B+ through the resistor 59. Accordingly the train of pulses is self-maintaining. These pulses are represented by flashes of the glow discharge tube 68 which we may now assume is to be stationary. If the water path .be interrupted as previously described the train of pulses is diminished in intensity or ceases altogether as soon as absorption of energy by the obstruction in the water path is sufficient. The glow discharge tube is then extinguished. The glow discharge tube is itself a responder but is preferably supplemented by the delay network d and responder R previously described.

If tube 56 is a vacuum instead of a gas tube oscillations can be obtained which form a periodic pattern in time which may be described as continuous rather than pulse modulated. A pulse signal pattern is preferred because with it more discriminatory information as to the nature and cause of the reduction of the transmitted signal may be obtained.

By the means described above a delayed action response system is provided which rejects casual reduction of the transmitted signal and gives a positive alarm desired when a reduction energy of predetermined minimum intensity has continued for a predetermined minimum duration of time. By the means disclosed it is possible to make a continuous search of the pool bottom which due to splashing of the water at its surface, or the low visibility of the water, or to lack of observers, would not otherwise be made. By the means described in Figure 2 a single signalling circuit can be employed to search" or keep watch over a pool area of substantial length and width.

It will thus be seen that there has been provided by this invention a method and apparatus in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As various possible embodiments might be made of the mechanical features of the above invention and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

What we claim is:

1. A system for detecting the presence of a body in a pool and giving an alarm which comprises, means for transmitting energy through water in a pool at a predetermined distance above the bottom of the pool, means for receiving energy transmitted to said means through water in said pool, alarm means, and means for actuating said alarm means when transmission of energy from said transmitting means to said receiving means is diminished more than a predetermined minimum amount for more than a predetermined minimum of time including, a source of energy, means for measuring the intensity of the energy, and means for measuring the time interval during which the energy intensity of the transmitted signal is diminished.

2. The apparatus claimed in claim 1 including means for collimating the radiated energy and means for directing and reflecting it so as to pass through a plurality of regions of the water in the pool.

3. The system for detecting the presence of a body 111 a pool and giving an alarm which comprises, means for propagating pulses of energy in water in the pool, means for receiving the energy after it is passed through water in the pool, an alarm device, separate means to actuate it, means for utilizing said energy to inhibit said separate means, and means for causing the alarm inhibiting means to be actuated only after the transmission of energy through the water in the pool has been diminished for more than a predetermined interval.

4. The apparatus claimed in claim 3 in which means are provided causing the alarm inhibiting means to be actuated only after a critical reduction of energy transmitted to the alarm inhibiting means is continued for a critical period of time.

5. Apparatus for detecting the presence of a body in a pool and giving an alarm which comprises means for propagating energy in water in a pool in groups of ultrasonic pulses, means for receiving the energy after it has passed through water in the pool, means for converting the received energy into electric energy, an alarm device, separate means for actuating said alarm device comprising an electric circuit, means actuated by the energy normally transmitted through the said pool to hold said alarm circuit open, the energy required by said last mentioned means being critical in amount, said means being actuated only when the energy transmitted through the pool exceeds a critical amount, and means for closing said circuit when the said means acting to keep it open is not energized.

References Cited in the file of this patent UNITED STATES PATENTS 2,071,933 Miessner Feb. 23, l937 2,411,537 Goodale Nov. 26, 1946 2,655,645 Bagno Oct. 13, 1953 FOREIGN PATENTS 656,399 Great Britain Aug. 22, 1951

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