AU3130701A - Pool alarm - Google Patents

Description

P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Name of Applicant: Actual Inventor Xplosive Electro-Acoustics Pty Ltd Michael Fragomeni Address for service is: WRAY ASSOCIATES 239 Adelaide Terrace Perth, WA 6000 Attorney code: WR Invention Title: "Pool Alarm" Details of Associated Provisional Application No(s): PQ6490 filed on 24 March 2001 The following statement is a full description of this invention, including the best method of performing it known to me:- -2- "Pool Alarm" Field of the Invention This invention relates to pools such as swimming pools and spa pools, and in particular to a device for monitoring pools to warn of unauthorised access or of a person in difficulty and at risk of drowning.

Background Art Death through accidental drowning in pools, and in particular backyard swimming pools is a significant problem. Various strategies have been adopted to prevent such deaths, including requiring owners of swimming pools in some jurisdictions to fence their pools off from the remainder of their property, in order to prevent unsupervised access by children. Beyond the placement of physical barriers, other systems have been proposed, such as placement of perimeter beams around the pool, which when broken will trigger an alarm state. An example of the latter is a perimeter infrared beam system proposed in US patent 4,910,498.

15 Other solutions proposed to the problem have centered around direct monitoring of the body of water, either by monitoring water level changes brought about by displacement changes caused by a body entering the water, or by monitoring ::"wave action caused when either a body falls in the water or through the struggling of a person in difficulty in the pool. U S patents 4,203,097, 4,775,854, and 5,910,772 are all examples of the latter, incorporating various mechanisms to sense the wave action.

It should be understood that knowledge of the publication of the above patent specifications is not an acknowledgement that any form part of the common general knowledge in Australia.

It is an object of this invention to provide an alternative pool alarm system that can detect splashing or other noises indicative of a person falling into or otherwise struggling or in difficulty in a pool.

-3- Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Disclosure of the Invention In accordance with the invention there is provided a pool alarm system including a transducer for placement submerged in a body of water contained in a pool, said transducer being connected to audio amplifier means for amplifying signals from said transducer, said audio amplifier being connected to level detection 10 means adapted to trigger alarm means when the level detected from said audio *°o*oo oo.amplifier exceeds a predetermined threshold, said pool alarm system having a peak sensitivity to frequencies lying in a frequency range of 1.2kHz to 4kHz and having a frequency response over said frequency range which is flat within *+12dB, and being at least 12dB less sensitive to audio frequencies at 400Hz than the sensitivity at 1.2kHz.

ooooo: Preferably said frequency range is from 1.2kHz to Preferably said frequency range is from 1.2kHz to 3.15kHz.

Preferably said frequency response over said frequency range is flat within Preferably said frequency response over said frequency range is flat within +9dB.

Preferably said frequency response over said frequency range is flat within ±8dB.

Preferably the sensitivity at 400Hz is at least 18dB less sensitive to audio frequencies at 400Hz than the sensitivity at 1.2kHz.

Preferably the sensitivity at 400Hz is at least 20dB less sensitive to audio frequencies at 400Hz than the sensitivity at 1.2kHz.

-4- Preferably the sensitivity at 400Hz is at least 22dB less sensitive to audio frequencies at 400Hz than the sensitivity at 1.2kHz.

Preferably the sensitivity at 400Hz is at least 23dB less sensitive to audio frequencies at 400Hz than the sensitivity at 1.2kHz.

Preferably the sensitivity at 400Hz is at least 24dB less sensitive to audio frequencies at 400Hz than the sensitivity at 1.2kHz.

Preferably said peak sensitivity lies between 1.5kHz and 2.5kHz, with -3dB corners in the frequency response of said pool alarm system being located at greater than 1.0 kHz and less than 3.3kHz.

10-' Preferably said peak sensitivity lies between 1.5kHz and 2.0kHz, with -3dB corners in the frequency response of said pool alarm system being located at greater than 1.0 kHz and less than 3.3kHz.

Preferably the roll-off in the frequency response below 1.0kHz is 18dB per octave or greater.

15 Preferably the roll-off in the frequency response above 3.3kHz is 6dB per octave or greater.

Preferably said -3dB corners occur at 1.2kHz and 3.15kHz.

a.

Preferably the roll-off in the frequency response below 1.2kHz is 18dB per octave or greater.

Preferably the roll-off in the frequency response above 3.15kHz is 6dB per octave or greater.

Preferably the roll-off in the frequency response below 1.2kHz is 24dB per octave.

Preferably the roll-off in the frequency response above 3.15kHz is 12dB per octave.

The inventor has found that with the frequency response parameters outlined above, false triggering which might occur with a broader frequency response due to low frequency noises transmitted through the ground (from footsteps and vehicular traffic), or from high frequencies that might be transmitted from the air, can largely be avoided. The inventors measurements suggest that noise arising from splashing in pools of most sizes has a peak frequency of around 1.6 kHz.

Preferably said pool alarm system includes a circuit to discriminate between background noises generated by pool cleaning devices and water jets and o spouts and the like, and splashing sounds and other noises indicative of an alarm state.

Brief Description of the Drawings Two embodiments of the invention will now be described in the following description made with reference to the drawings, in which: Figure 1 is a cross-section view of a transducer in a swimming pool alarm utilised in either embodiment; Figure 2 is a block diagram of the swimming pool alarm according to the first embodiment; 20 Figure 3 is a circuit schematic of circuitry for the first embodiment; Figure 4 is a graph of the frequency response of the swimming pool alarm according to the first embodiment; Figure 5 is a circuit schematic of circuitry for the second embodiment; and Figure 6 is a graph of the frequency response of the swimming pool alarm according to the second embodiment.

Best Mode(s) for Carrying Out the Invention Referring to figure 2, the swimming pool alarm is shown as a block diagram. The swimming pool alarm has a transducer 11 which is intended for placement within -6a body of water in a swimming pool, spa pool, or other ornamental pool. The transducer 11 connects to the circuitry of the swimming pool alarm, the circuitry comprising a transducer preamp 13 featuring gain adjustment 15. The output 17 of the transducer preamp 13 connects to a high-pass filter 19 having a 24dB/octave roll off, and a lower -3dB point at 1.2kHz.

The output 21 of the high-pass filter 19 is fed to a level detect circuit 23 having threshold level adjustment 25. When the signal level at the output 21 of the high pass filter 19 reaches a predetermined threshold, a signal is provided at the output of the level detect circuit 23 and fed to a latch circuit 27, which when the swimming pool alarm is armed, latches on and provides a signal at its output 28 to cause an alarm sounder and warning light to operate.

Control over arming and disarming of the swimming pool alarm is effected by a .o remote control receiver and associated circuitry 29. The remote control receiver and associated circuitry 29 has a status output 31 which is at a logical high when the swimming pool alarm is disabled, and at a logical low when the swimming pool alarm is enabled. The remote control receiver and associated circuitry 29 .o also has a reset output 33 which supplies a logical high pulse to reset the latch circuit 27, on disarming the swimming pool alarm. This resets the swimming pool alarm after the alarm has been triggered. A remote control transmitter 35 is provided to actuate the remote control receiver and associated circuitry 29 and thus control operation of the swimming pool alarm. The remote control S•transmitter 35 has a push-to-make switch 37 for arming, and a push-to-make switch 39 for disarming the swimming pool alarm.

Turning to figure 1, the transducer 11 has a body 41 within which is encapsulated in epoxy resin 43, a moving coil microphone 45 connected to its output lead 46.

The microphone 45 is located behind a perforated wall 47 in the body. On the other side of the perforated wall 47 from the microphone 45 is mounted a piece of acoustic foam 49, on the front/sound input side of the transducer. This is sealed against ingress of moisture by a plastic diaphragm 51.

-7- In figure 3 the circuit schematic for the swimming pool alarm circuitry, excluding the remote control receiver and associated circuitry 29 and the remote control transmitter 35 is shown. A power supply circuit 53 derives a split rail power supply required by opamps in the circuitry, from a 13.8v DC single rail power supply. Two opamps 55, 57 provide the preamp 13 in the form of a two stage preamplifier for the transducer. Opamp 57 has a preset-type potentiometer 59 to provide some control over the gain (gain adjustment 15) of that stage of the preamplifier. Taking advantage of the high gain of the stage of the preamplifier centered around opamp 57, the opamp 57 and its immediate associated circuitry provide a low pass filter having, at maximum gain 53.9dB gain at 20Hz and 33.9dB gain at 20kHz, with a -3dB point at approximately 2.02kHz.

V 996.

The output of the preamplifier (from opamp 57) is fed to a high pass filter 19 i having 24dB per octave roll off and a -3dB point at approximately 1.2kHz. The high pass filter 19 is formed by two identical high pass filter stages in series, each stage having a roll off of 12 dB per octave, unity gain, and a lower -3dB point at 860Hz. The two stages are centered around opamps 61 and 63 oeeeo respectively.

ooe.

The level detect circuit 23 is centered around transistors 65 and 67, with threshold level adjustment 25 being provided by potentiometer 69. The status output 31 of the remote control receiver and associated circuitry 29 is fed to *status input 71. When the alarm is disabled, the voltage at the status input 71 is high, which turns on transistor 73, preventing signals from the transducer from actuating the swimming pool alarm into an alarm state. When the alarm is enabled, the voltage at the status input is low, and transistor 73 is turned off. This allows a signal picked up by the transducer, of sufficient strength and within the correct bandwidth, to cause the SCR 75 to turn on, switching on (via the output 28a strobe and a siren 77 connected thereto, to indicate an alarm state. SCR is by its nature a latching device, as will be understood by a person skilled in the art; thus, once triggered into an alarm condition, the strobe and siren 77 will continue to operate -8- Once in the alarm state, disabling of the alarm, in addition to switching the voltage level at the status input to a high level, supplies a short high level pulse to the disarm input 79, which briefly turns on transistor 81, diverting current from SCR 75, causing SCR 75 to turn off.

The remote control transmitter 35 and remote control receiver are standard code scrambling units which are commonly employed in automotive vehicle security applications. Associated circuitry referred to in relation to the remote control receiver and associated circuitry 29 comprises simple modifications that may need to be made in order to provide the required signals to the status input 71 and the disarm input 79. Also included in the associated circuitry, are status indicator lamps, to shown whether the swimming pool alarm is armed or disarmed. All details referred to in relation to the associated circuitry are considered to be well within the grasp of the skilled addressee, and are not described here.

In use, the transducer should be located in the pool, at least 15cm below the surface of the water. A depth of 65 cm for locating the transducer should prove oooo suitable, although tests at a depth of 120cm showed the swimming pool alarm to be quite sensitive. It is preferred to avoid placement of the transducer on the *-•..bottom of the pool, due to increasing the low frequency sensitivity. In practise, the transducer can be located in the side of the pool, at a depth of between and 120cm, with plastic diaphragm 51 facing toward the centre of the pool. A fibreglass pool could be prefabricated to receive a transducer, or could be supplied with the transducer already fitted.

The circuitry of the second embodiment is shown in figure 5. The second embodiment differs from the first embodiment, in two major respects. Firstly, the power supply, which is not shown, is a ±1 2V power supply, rather than a +6.9V power supply as utilised in the first embodiment. This allows higher amplification levels to be achieved in the second embodiment, with attendant advantages in signal to noise ratio.

-9- Secondly, the high pass filter (indicated at 19 in the first embodiment) is formed from three stages, each stage centered around opamps 83, 85, and 87. Each high pass filter has a 12dB per octave roll-off, with narrow Q alignment, resulting in some roll-off toward higher frequencies. This obviates the need for preamplifier centered around opamp 57 to function as a low pass filter, so in the second embodiment the preamplifier centered around opamp 57 has a substantially flat frequency response.

The -3dB points for the high pass filter centered around opamp 83 are 1.35kHz and 2.24kHz, the center frequency being 1.78kHz, and gain at the center frequency being 23.4dB. The -3dB points for the high pass filters centered around opamps 85, and 87 are both 1.95kHz and 3.32kHz, the center frequency oooo for both being 2.52kHz, and gain at the center frequency being 23.8dB. The ii:*l overall response gives -3dB points at 1.95kHz and 2.9 kHz, -12dB points at 1.39kHz and 3.16kHz, and a response of approximately -20dB at 1.2kHz.

The result of these difference is greater selectivity in the second embodiment, when compared with the first.

The other minor difference in the second embodiment is the opamp 55 which forms a buffer, has an RC network 89 preceding it which forms a gentle high pass filterwith slope of 6dB per octave and a -3dB point at 726Hz. This 20 arrangement provides mains hum rejection which might be induced due to mains Swiring for pool lighting or pool filter pumping or the like.

A pool fitted with an alarm according to the invention can be used to warn of unauthorised or unsupervised entry by a person to a pool. With the frequency response of the pool alarm of the invention, the alarm can be set off by a person in difficulty splashing around on the surface of the water, screaming or yelling under the water, or possibly even scratching on the bottom of the pool (although this is dependent on the construction materials used in the pool). With the relative insensitivity to frequencies below 1.2kHz, the swimming pool alarm is relatively insensitive to noise produced by pumps and pool accessories, while being quite sensitive to the frequencies of sound indicative of a person in difficulty in the pool.

Various modifications can be made without departing from the invention. The swimming pool alarm could be interfaced to activate in-pool and pool side lighting, be interfaced to lock and unlock pool enclosure gates with the arming and disarming of the alarm. In addition, a detector could be incorporated to detect access through pool enclosure gates or doors, so the alarm could be triggered by such access, when armed. Furthermore, the swimming pool alarm may incorporate an interface with noise producing pumps and pool accessories, to change the sensitivity of the swimming pool alarm, so that the pool alarm can be more sensitive when these devices are not in operation.

sees The swimming pool alarm can be powered from mains, with rechargeable battery backup, electrical solar cell with rechargeable battery, or even by a small hydroelectric generator in-line with the pool pump, supplying electricity to a rechargeable battery.

It should be appreciated that the scope of the invention is not limited to the :9 .,particular embodiment described herein.

9

Claims (14)

1. A pool alarm system including a transducer for placement submerged in a body of water contained in a pool, said transducer being connected to audio amplifier means for amplifying signals from said transducer, said audio amplifier being connected to level detection means adapted to trigger alarm means when the level detected from said audio amplifier exceeds a predetermined threshold, said pool alarm system having a peak sensitivity to frequencies lying in a frequency range of 1.2kHz to 4kHz and having a frequency response over said frequency range which is flat within ±12dB, *°oo 10 and being at least 12dB less sensitive to audio frequencies at 400Hz than the sensitivity at 1.2kHz.

2. A pool alarm system as claimed in claim 1 wherein said frequency range is from 1.2kHz to ooooo S-3. A pool alarm system as claimed in claim 1 wherein said frequency range is from 1.2kHz to 3.15kHz.

4. A pool alarm system as claimed in any one of the preceding claims wherein said frequency response over said frequency range is flat within A pool alarm system as claimed in claim 4 wherein said frequency response over said frequency range is flat-within +9dB.

6. A pool alarm system as claimed in claim 4 wherein said frequency response over said frequency range is flat within +8dB.

7. A pool alarm system as claimed in any one of the preceding claims wherein the sensitivity at 400Hz is at least 18dB less sensitive to audio frequencies at 400Hz than the sensitivity at 1.2kHz. -12-

8. A pool alarm system as claimed in claim 7 wherein the sensitivity at 400Hz is at least 20dB less sensitive to audio frequencies at 400Hz than the sensitivity at 1.2kHz.

9. A pool alarm system as claimed in claim 7 wherein the sensitivity at 400Hz is at least 22dB less sensitive to audio frequencies at 400Hz than the sensitivity at 1.2kHz. A pool alarm system as claimed in claim 7 wherein the sensitivity at 400Hz is at least 23dB less sensitive to audio frequencies at 400Hz than the sensitivity at 1.2kHz. 10 11. A pool alarm system as claimed in claim 7 wherein the sensitivity at 400Hz is at least 24dB less sensitive to audio frequencies at 400Hz than the sensitivity at 1.2kHz.

12. A pool alarm system as claimed in any one of the preceding claims wherein said peak sensitivity lies between 1.5kHz and 2.5kHz, with -3dB corners in 15 the frequency response of said pool alarm system being located at greater than 1.0 kHz and less than 3.3kHz.

13. A pool alarm system as claimed in claim 12 wherein said peak sensitivity lies between 1.5kHz and 2.0kHz, with -3dB corners in the frequency response of said pool alarm system being located at greater than 1.0 kHz and less than 3.3kHz.

14. A pool alarm system as claimed in claim 13 wherein said -3dB corners occur at 1.2kHz and 3.15kHz. A pool alarm system as claimed in claim 14 wherein the roll-off in the frequency response below 1.2kHz is at least 24dB per octave.

16. A pool alarm system as claimed in claim 12 wherein said peak sensitivity lies between 2.0kHz and 2.5kHz, with -3dB corners in the frequency -13- response of said pool alarm system being located at greater than 1.5 kHz and less than

17. A pool alarm system as claimed in claim 14 wherein said -3dB corners occur at 1.95kHz and 2.9kHz.

18. A pool alarm system as claimed in claim 14 wherein the roll-off in the frequency response below 1.2kHz is at least 36dB per octave.

19. A pool alarm system substantially as herein described with reference to any one of the embodiments. 0 ~Dated this twenty sixth day of March 2001. Xplosive Electro-Acoustics Pty Ltd Applicant g Wray Associates Perth, Western Australia Patent Attorneys for the Applicant o