US 3760396 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
1 11 111 3 3 9 3 I I 1 11a :meonaae v I o j Umted States Pat X 7 95 5, 13,760,396 Haselton v a/za 4 1 in. 18,1973
[ 1 BOAT AND SWIMMING POOL INTRUSION 2,935,582 5/1960 Northey 340/261 ux DETECTOR 3,530,267 9/1970 Whitmore 200/83 R 1,029,598 6/1912 Davies 73/301  Inventor: Frederick R. Haselton, 1205 Fallsmead Way, Rockville, Md. FOREIGN PATENTS OR APPLICATIONS 20854 344,167 10/1904 France 340/242  Filed: June 2, 1971 Primary Examiner-John W. Caldwell 1 PPJ- -1 1 I 1 AssistantExaminerDaniel Myer Related Us. Application Data Attorney-George Vande Sande  Continuation-impart of Ser. No. 106,145, Jan. 13, v
1971, abandoned.  ABSTRACT 7 An alarm system for use on boats or other water craft.  US. Cl. 340/240, 73/301, 200/83 N The base displacement of the boat is altered when an 1211 215.11' $51.73;:3;::JJJJJJJJiJjjj:5x5 llflf the when is shipped in the bilge. The increased displacement is monitored in a pressure-sensitive chamber, and if the displacement exceeds a predetermined level, a switch in the pressure-sensitive chamber is. activated, thereby 340/261; 114/122,125;73/181-183, 406, 407, 308, 301; 200/83 R, 83 N, 83 Q, 83 S o ['56] References Cited triggering an alarm. The alarm system is also applicable UNITED STATES PATENTS to swimming pools. The water'level in a pool will rise 842,856 2/1907 Calder. 114/125 if an intruder enters the P or if someone inadver- 2,l43,l03 1/1939 Cox 200/83 N X tently falls. The change in pool water level is monitored 9 3/1960 Sanders 73/406 X in a pressure-sensitive chamber, and if the change ex- 31475v746 10/1969 Ne|sn 340/261 ceedsa predetermined level, an alarm is energized. 484,642 10/1892 Patterson 73/308 v 2,723,388 11/1955- Jacobs 340/236 16 Claims, 6 Drawing Fignres Patented Sept. 18,1973 3,760,396
IIIIIIIQT I l. ALARM F IG 3 43 J 1 I/ ALARM \C -o o-1 l AMPLlFlER/ AND RELAY 1 r BATTERY 47 INVENTOR Frederick R. Hose/ton BOAT AND SWIMMING POOL IN'IRUSION DETECTOR SUMMARY OF THE INVENTION til electronic instruments, and are generally moored in a distant location without adequate lighting or patrols. They are generally unattended most of the time and are easily boarded from a small pram or skiff.
Likewise, unattended swimming pools require either an adequately safe enclosure or fence, or an intruder alarm for safety measures.
Many existing types of alarms leave much to be desired. If the alarm is incorporated into the wiring system of the equipment, it is possible for a thief to disconnect the battery or, in some cases, even to disconnect the alarm device. If the alarm is of the capacitance type which senses the presence of a mass near the boat, it can be activated by birds, large schools of fish, or innocent passersby in small boats.
It is therefore an object of the present invention to provide an alarm system for pleasure boats or swimming pools which will detect and activate an alarm when the boat or pool is boarded or entered byi'an intruder or unauthorized person. The present invention will sense an increase in the displacement of the boatcaused by the additional weight. In doing so, it will also sense any Le lgsg excessive water shipped aboard during a storm or hull failure. In acting as a flooding detector, the alarm system is activated before the water level within the boat rises to a level sufficient to cause damage to the engine and sophisticated electronic instruments therein. It also will detect an increase in pool water-level caused by an intruder.
It is also an object of the present invention to provide an alarm system which will be unaffected by the roll or pitch of a boat at anchor caused by passing vessels, or by prevailing windor chop. Similarly, the device will be unaffected by wind waves in a pool.
It is a further object of the present invention to provide an alarm device which senses an increase in displacement due to the addition of weight. A fairly large pleasure boat which v may have a waterline crosssectionalarea of 1,000 sq. feet will sink approximately two one-hundredths inch if a 100-pound man comes aboard; whereas, a small boat with an approximate waterline area of 100 sq. feet will sink two-tenths inch for the same additional weight. Inasmuch as water tends to seek a common level, this motion may be transferred to a fixed chamberlocated within the boat at or below the waterline of the vessel. This fixed container or chamber means is equipped with a diaphragm that will sense an increase in pressure caused by the rising water level within the sealed chamber. This increase in pres sure is translated intomotion of a diaphragm, said motion then activating a switch means which will trigger the alarm. The same principle is involved in sensing a rise in water level of a pool.
It is also an object of the present invention to provide an alarm system which will compensate for pitch or roll of the vessel by locating a plurality of secondary chamber means at the outer periphery of the boat and then connecting them in parallel to the sealed chamber means.
It is another object of this invention to accurately de- I termine a precalculated draft measurement of large vessels used to transport cargo. At present cargo vessels are marked with Plimsoll marks both forward and aft on the hull to indicate maximum legal loadings. My invention will provide a more precise measurement and will allow the owner to most effectively load his cargo for maximum revenue.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional and schematic view of the sealed chamber and alarm system utilized in the present invention.
FIG. 2 is anisometric drawing illustrating an alternate version of the present alarm system mounted within the water vessel.
FIG. 3 is a cross-sectional view of the chamber device and alarm system utilized in the embodiment illustrated I in- FIG. 2;
FIG. 4 is a schematic drawing of the electrical system for the alarm device illustrated in FIG. 1.
FIG. 5 is a cross-sectional drawing of apool illustrating the manner in which the alarm system ismounted.
FIG. 6 is a schematic drawing of the electrical system for automatically cycling the pool alarm system illustrated in FIG. 5.
DETAILED DESCRIPTION Referring to FIG. 1, a casing 11 is mounted securely within the boat or water vessel to be protected at or below the waterline of the boat. Diaphragm means 12 extends across the interior of the chamber dividing it into a first sealed chamber means 13 and a second chamber means 14. This diaphragm is firmly affixed.
and sealed to upstanding wall means 15 and 16 at points 17. and 18.
The cross-sectional view illustrated in FIG. 1 is that of a cylinder container, but it may be any polygon such as a square, rectangle, hexagon, or virtually any other shapewhich may be conveniently separated into a first and second chamber means by the diaphragm 12. Conduit means 19 communicates with and extends from the water below the waterline of the vessel to the first chamber means 13. Since casing 11 is mounted at or near the waterline of the vessel, the water entering via conduit means 19 will rise and cause diaphragm 12 to flex upwardly as illustrated in FIG. 1. A second conduit means 32 communicates and extends from the second chamber means 14 to a point well above the water level outside the boat or pool. Conduit 19 is equipped with a valve 22 which may regulate or stop the flow of fluid in the conduit.
An adjustable switch means 25 is mounted within the second chamber adjacent to said diaphragm means 12. This switch has an electrically conductive plate 24 mounted on diaphragm 12, and an electrically conductive probe 25 which is adjustably extended through the exterior wall of casing 11 to contact the plate 24. The contacts 24 and 25 of the adjustable switch means are connected to the alarm system via conductors 26 and 27. As the diaphragm fluctuates up and down, the electrical contact plate 24 is. moved in and out of contact with probe 25, thereby activating or deactivating the alarm system. The alarmsystem is illustratedin FIG. 4 and is comprised of a battery 28'which is connected toequilibrium with no forces other than gravity andbuoyancy present. To activate the alarm system, the seav cockor' globe-valve 22 is opened to allow the water to flow into conduit 19. As the water level rises within the conduit, a positive pressure is generated in chamber 13 causing the membrane to flex upward. The upper chamber 14 vents the displaced air to the atmosphere I by means of vent conduit 32. The high neck portion of conduit 32 prevents the entry of water into the boat in the event diaphragm l2 ruptures. The flexible diaphragm 12 also prevents the contamination and corrosion of the adjustable switch means, and its contact 24 and 25 by water or salt water vapor entering conduit 19. Flexible diaphragm 12 is sealed about the inner surface of chamber 11 as illustrated at 17 and 18. The contacts are further protected from arcing or heavy loads by means of the amplifiers 23 and relay 30. This permits a small current flow through the contacts, but will trigger a relatively heavy current flow through the alarm device 29.
In'setting thealarm system after installation, valve 22 is first throttled to a nearly closed position. The adjustment of valve 22 is important as it will permit discrimination between wave motion and unauthorized weight.
Wave motion itself will tend to cause pressure fluctuations within the first chamber means 13. The sudden matic remote adjustment features provided, the probe may be automatically spaced from plate 24 in a manner. of seconds.
Similarly, the features also are desirable when the device is used as an automatic loading device for cargo ships or freighters. These large vessels must precisely determine the amount of cargo they are carrying since rocking or displacement of the boat by wind, waves,
chop, or the wake of a passing boat would cause the flexible diaphragm to rapidly rise and fall in an attempt to balance the external waterline and pressure head.
These diaphragm fluctuations are prevented by closing valve 22 an appropriate amount which mitigates against these transient pressure changes, while permitting a smaller flow caused by a steady pressure differential. Thus, the detection may take as long as a minute for a large boat but proportionately shorter times for smaller boats.
After throttling back valve 22, the adjustable contact 25 is brought into contact with plate 24 by a screw adjustment 33 as illustrated in FIG/1. This activates the alarm while the owner of the boat'is within. Ashe leaves the boat, the boat rises, and its exterior waterline drops, thereby drawing down the diaphragm covering the first chamber means 13. As the waterline drops, the static pressure in chamber 13 is lowered allowing diaphragm 12 to draw away from the adjustable contact 25'and breaking the alarm circuit. The alarm is thus set to detect any increase of total boat weight which may be caused by an unauthorized boarder or by additional water in the bilge.
FIGS. 1 and 4 also disclose an automatic remote adjustment to automatically adjust probe 25 to its proper spacing from diaphragm l2 and plate 24. This feature is especially desirable when leaving the boat since any change in loading, fuel, provisions or the like may have changed the gross loading of the boat which would require a manual adjustment of probe 25. With the autothe amount of cargo and their draught is regulated by law.'My invention is particularly suited to determine the gross loading of the vessel, and the automatic remote adjustment feature makes it possible for the captain or'harbor master to accurately determine loading of the vessel from a remote location.
' As illustrated in FIG. 1, a motor is provided to drive the probe upwardly and downwardly, in and out of contact with the switch contact mounted on diaphragm 12. This is accomplished by the circuitry disclosed in the dotted box of FIG. 4. h
A phase mode switch 62 is provided to provide three modes of operation. The first causes the motor to oscillate, driving the probe 25 in and out of contact with plate 24. This provides for the automatic remote adjustment of probe 25 in the event there are large changes in gross loading. This feature enables the probe to find contact plate 25 and home on it as it oscillates back andforth. This is accomplished by adding two additionalpoles to'relay 30 to provide field reversal for motor 20. Y
The second mode of operation will suspend the probe above contact plate 24 a certain predetermined amount. This is accomplished by letting motor 20 drive probe 25 into contact 24, and then reversing the field of the motor at that instant so that it is driven away from the contact and simultaneously breaks the current driving motor 20. The overshoot of the motor will carry probe 25 a certain predetermined distance away from plate 24. The amount of overshoot desired is regulated by a variable resistor placed in the motor winding.
Referring to FIG. 1, the adjustable switch means 25 is equipped with a small electric motor 20 mounted on guide rail 31 for reciprocal movement in a path parallel to the movement of probe 25. The output of motor 20 drives spur gear which, in turn, drives the large spur gear 81 mounted on probe 25. Thus, as motor 20 is energized, probe 25 will rotate causing the screw threads 82 to advance probe 25 throughthe threaded bosses 83 and 84. Alignment anns 85 and 86 are provided on the motor casing to ensure that the spur gears 80 and 81 are maintained in a meshing relationship. As the probe 1 25 is driven downwardly by motor 20, the collar means 87 mounted on probe 25 will force the motor down along guide rail 31. When the direction of the motor is reversed, and probe 25 is driven upwardly, the collar 88 will drive motor 20 upwardly along guide rail 31.
The electrical circuitry for driving motor 20 is disclosed in FIG. 4 within the dotted outline. Switch 62 is the phase load switch which determines the mode of operation for motor 20. As indicated in FIG. 4, relay 30 now becomes a triple pole, double throw relay, and switch 69 becomes a double pole, triple throw switch. In its first mode of operation, the alarm device 29 is disconnected, and contact is made between contacts 62 and 63. Relay 30 is a current reversal relay for motor 20 and provides for the automatic reversal of motor 20. The electrical current entering the motor circuitry at relay pole 30B passes to contact 92, and through variable resistors 67 to motor 20. The return circuit is completed through contact 63, switch 62, and contact 94 of relay pole 30C. In this first phase, motor 20 drives of relay 30. This field reversal enables motor 20 to drive probe 25 upwardly out of contact with plate 24.
In doing so, it will de-energize relay 30, and cause another subsequent reversal of the field in motor 20. Thus, motor 20 will continue to oscillate, driving the probe 25 in and out of contact with plate 24, but with the probe remaining in quite close proximity with plate 24 even when at its maximum distance from the plate.
presence. Also, if the boat were moored and a steady In the second mode of operation, switch 62 makes I of contact with 24, relay 30 will be de-energized and motor will then become inactive.
The adjustable resistor 67 shown in the motor control circuitry in FIG. 4 allows a torque adjustment for the motor, which will regulate the amount of motor overshoot and thus the amount the contacts 24 and 25 open and close on each reversal. It also provides a method for automatically predetermining the distance that probe 25 is suspended above 24 when the circuit is in its second mode of operation.
During the first and second modes of operation,
' switch 69 has been disconnected, and alarm means 29 has been silent. Light 68 however will flash on and off as the probe makes contact with plate 24. As motor 20 oscillates back and forth, light 68 will provide a'flashing indication that the circuit is functioning properly. When switch 62 is placed in its second mode of operation, light 68 will flash once and then go out as the automatic remote adjustment provides for the proper adjustment between probe 25 and plate 24.
' After the proper distance has been established, switch 62 is placed in its third mode of operation which completely disconnects the motor control circuitry and energizes alarm 29.
ln operation,.as the owner of the vessel prepares to leave, he places the load selector switch 62 in its first position. The flashing light 68 will indicate that the circuit is functioning properly, and that the remote adjustable probe 25 is in its approximate location. After he leaves the boat, he places the mode selector switch 62 in its second position and waits until light 68 has flashed once. After it is extinguished, he places the mode switch in its third mode of operation, deactivating the motor circuitry 20, and activating alarm circuitry 29.
An alternate version of the invention is disclosed in FIG. 2. As pointed out previously, the ideal placement of the sealed chamber is in a line orthogonal to and below the geometric center of the waterline place of the boat when it is in equilibrium with no forces other than gravity or buoyancy present. If it were located on the port side, and a boarder came aboard and remained on the starboard side, the sensor would not detect his wind came up, the resulting heel would cause the sensor to either be disabled, or to activate the alarm. Unfortunately, the ideal location may prove inconvenient, particularly in small boats. The improved embodiment of my invention alleviates these problems.
As disclosed in FIG. 2, the improved embodiment comprises a third pair of waterline chambers and 41 mounted on the port and starboard sides of the boat. In
addition, it would also be feasible to mount additional waterline chambers in the bow and stem of the boat to prevent the disabling or activation of the alarm during pitch as well as roll. These waterline chambers are connected in a parallel flow pattern from the water inlet 42 to the sealed chamber device generally illustrated at 43 by means of parallel conduits and 46. Sea cock 44 is open to allow the water within the system to fill the waterline chambers to the level indicated by the waterline on the exterior of the boat. After the interior water levels are static, the sea cock 44 is throttled back to prevent sudden fluctuations in the pressure system due to sudden movements of the boat. Although the sealed chamber 43 is mounted in the ceiling of the boat cabin, it may be mounted anywhere within the boat.
The ratio of air volume to waterline area is important. The total area of the air-water interface in the waterline chambers must be sufficiently large, in relation to the total volume of air in conduits 45 and 46, that the vertical'displacement of the water by two-tenths to two one-hundredths of an inch will cause a significant increase in the air pressure in conduits 45 and 46. By choosing an appropriate ratio, one can increase or decrease the sensitivity of the system. The sensitivity could be doubled by making the square area of the airwater interface twice the area of the diaphragm 49.
Once the static equilibrium has been achieved in the system, a roll to starboard will raise the water level in the starboard secondary chamber, and lower the water level in the port secondary chamber. Thus, the air pressure maintained in conduits 45 and 46 is essentially static. Conversely, if the sensors weremounted fore and aft and the stern was suddenly raised by the wake of a passing vessel, the waterline within the stern sensor would drop while the waterline in the bow sensor would rise.
The waterline chambers should be symmetrically spaced from the center line of the boat. Their vertical dimensions when installed should be great enough that the air-water interface remains within the chamber at all probable heel and pitch angles the boat will encounter while moored.
The device 43 is illustrated in cross section in FIG. 3. Conduits 45 and 46 are connected with a common T- fitting 47 to the sealed chamber means 48. Diaphragm means 49 extends across the interior of the sealed chamber 48 and provides a first chamber means 50 and a second chamber means 51. A secondary conduit means 52 connects the first and second chamber means and allows adjustment of water level in chambers 40 and 41 by means of valve 53. An air vent 54 is placed in the upper chamber to allow fiecture of the diaphragm 49. Adjustable switch means 55 has a first contact 56 mounted on diaphragm 49, and a secondcontact 57 mounted on the adjustable probe means 58. These switch contacts are then connected to the amplifier 23 and relay 30 illustrated at 59 which will trigger alarm 60 when the contacts 56 and 57 are clos'ed. Relay 30 again acts as the buffer between the switch 55 and the alarm 60 to prevent the high load currents present in the activated alarm from arcing or otherwise impairing the electrical contacts 56 and 57. The second chamber means 51 is likewise sealed against the entry of dust, sea water, or other contaminants except for the small vent tube 54 to ensure that the electrical contacts 56 and 57 are clean and functioning.
The operation is essentially similar to that disclosed I for FIG. 1. The sea cock 44 and valve 53 are opened,
and the water is allowed to rise to its static level as indisea cock 44 is then throttled back to prevent any sudden fluctuations in pressure due to wave motion or chop. After the pressure has reached a static equilibrium, the adjustable probe 58 is screwed down to acti- I ment for the boat and a rise of the external waterline.
As the external waterline rises, the internal air-water interface in the waterline chambers will rise causing an increase. in the air pressure in conduits 45, 46 and chamber 50. This will flex the diaphragm upwardly,
closing contacts 56 and 57 and triggering the alarm circuit. The alarm, as before, is powered by a'battery source means 61.
While the electrical system illustrated in FIG. 3 has been shown in conjunction with the waterline chambers of FIG. 2, it would be entirely feasible to use the alarm device indicated in FIG. 1 with the displacement. chambers indicated in FIG. 2. This would provide the automatic and remote adjustment of contact probe 'cated in FIG. 2. At that time valve 53 is closed and the when the owner is leaving his vessel. The present alarm V system may also be adapted to large freighters or other cargo vessels where loading limits are regulated by law. The current practice is to paint Plimsoll marks on the bow and stem of each such vessel carrying a cargo.
These are at best a crude indication and indicate only I the maximum draft marks for salt and fresh water. A
manually operatedversion of the alarm shown in FIG. 1 could be calibrated to allow for any density of water, and a pluralityof units could be mounted with two units forward and two units aft on the starboard and port sides of the vessel to indicate to the ship master or harbor master precisely when the legal tonnage has been placed on board. This would also enable the captain of the ship to determine the optimum distribution of the cargo or loading. a
While the system as described thus far has been entirely electrical in nature, it would be an obvious modification to one skilled in the art to substitute a mechanical switch means, and a'mecha nical alarm such as a Freon air gun or siren.
The alarms 29, 60 and 87 have been generally indicated as accoustic alarms. However, the alarm could also be connected to flashing lights, or the running lights of the boat, or even to a wireless or radio telephone signalling device. These other alarm devices could be used as needed depending on the mooring of the boat, and the alarm necessary to attract attention to the mooring.
FIG. 5 is an illustration of the alarm device adapted for installation in a swimming pool. The alarm device 11 is fixed to the side of the pool below the normal water level with vent 32 protruding above the water level. In this application, the device illustrated in FIG. 1 would be used with the control shaft and probe 25 being wholly self-contained within casing 11 thereby preventing any undesired leakage through threads 82 and 83. Conduit 19 would be open to the water surrounding chamber 11 and valve 22 would again be" throttled tominimize the effect of wind and chop on the surface of the swimming pool. Because the pool water level will vary with evaporation and rain fall, frequent adaptation is required to maintain the desired sensitivity of the device to detect a person or other object entering the pool. This is accomplished by provid ing an automatic cycling switch and timer.
As illustrated in FIG. 6, switch 62 and 690i FIG. 4 are coupled or ganged together in a double pole triple throw rotary switch by means of shaft 100. Shaft is rotated by motor 101 which is in turn actuated by timing means 102. The timing means, which is well known in the art may be set to begin its cycle every 15 minutes. Upon completion of the 15 minute cycle, motor 101 is energized and drives switches 62 and 69 through each of the respective three positions. As shown in FIG. 6, switch 62 is thrown to contact 63, and switch 69 is disengaged so as to not activate the alarm. During the first stage of the timing cycle the probe will oscillate up and down as herein before described with respect to FIG. 4. When the second stage of the timing cycle motor 101 will drive switch pole 62 and 69 to the second position wherein switch pole 62 will make contact with contact 64. During this phase of the timing cycle the probe 25 will automatically readjust itself to a short disance above contact 24 as previously described in the operation of FIG. 4. During the third phase of the timing cycle motor 102 will drive pole 62 and 69 into the third position wherein pole 62 will come into contact with contact 65 and thereby disengaging the motor circuitry and engaging switch 69 with its alarm circuitry. The first two phases of the timing cycle may be completed in 5 to 10 seconds, and the third phase of the timing cycle will be the remainder of the 15 minute period. Thus every 15 minutes the alarm device will reestablish the probe position for its correct placement taking into account any slight gradua changes from rain fall or evaporation. Y
1. An alarm device for water vessels comprising a. a casing which defines a chamber, said casing being mounted within said vessel and including a diaphragm mounted therein to divide said chamber into first and second portions;
b. conduit means communicating with and extending from a water inlet means below the water lineof said vessel to said first chamber portion, said conduit means including means for restricting the rate of the water flow through said conduit means to said first portion of said casing to render said diaphragm non-responsive to transient pressure variations caused by rolling, pitching and heaving of the vessel, but responsive to steady pressure variations caused by an increase in the vessel's mean displacement;
c. said casing blockingthe flow of water from below the vessels water line into said second chamber portion;
d. switch means mounted within said second chamber and responsive to flexure of said diaphragm to actuate said switch means as the displacement of the water vessel is increased beyond a predetermined value,
e. means for adjusting the position of at least part of said switch means relative to said diaphragm to control thereby the particular position of said diaphragm causing actuation of said switch means,
f. and signal means connected to said switch means for providing a distinctive signal when said switch means is actuated.
2. An alarm device as claimed in claim 1 wherein said conduit means further comprises:
a. at least two conduit means communicating with and extending from the water inlet means to said first chamber means, said conduits being connected in a parallel flow pattern between said inlet and said first chamber means;
b. each of said conduits further defining an enlarged waterline chamber mounted within said vessel at or below the waterline of said vessel.
3. An alarm device as claimed in claim 1 wherein a second conduit means connects said first and second chambers, said second conduit having an adjustable valve means mounted therein between said chambers.
4. An alarm device as claimed in claim 1 wherein said switch means and said alarm means are electrical.
5. An alarm device as claimed in claim 4 wherein a first electrical contact to said switch means is mounted .on said diaphragm, and a second electrical contact is adjustably mounted within said second chamber.
6. An alarm device as claimed in claim 5 wherein said second adjustable contact may be adjustedexternally of said chamber.
7. An alarm device as claimed in claim 5 wherein a relay means is energized by switch means, said relay energizing said alarm means.
8. An alarm device for water vessels as claimed in claim 1 wherein each of said first and second chamber portions is contained within said casing.
9. An alarm device as claimed in claim 1 wherein said means for restricting said conduit comprises valve means mounted in said conduit to adjustably restrict the flow of water therethrough.
10. An alarm device which comprises:
a. a casing, said casing defining a chamber and including a diaphragm mounted therein to divide said chamber into first and second chamber portions; b. conduit means communicating with and extending from a fluid inlet means below the level of a body of fluid to said first chamber portion, said conduit means including means for restricting the rate of fluid flow through said conduit means to said first chamber portion to render said diaphragm nonresponsive to transient pressure variations caused by wave motion, but responsive to steady pressure variations caused by increased mean fluid pressure at said fluid inlet means;
c. said casing blocking the entry of water from said body of water into said second chamber portion; d. switch means mounted within said second chamber portion;
e. means responsive to flexure of said diaphragm to actuate said switch means as the fluid pressure increases beyond a predetermined value;
f. means for at times automatically adjusting the position of at least part of said switch means relative to said diaphragm to compensate thereby for varying levels of fluid in said body of fluid;
g. and alarm means connected to said switch means to be energized when said switch means is actuatedv i 11. An'alarm device as claimed claim 10 wherein said switch means includes a first contact means suspended above said diaphragm, said contact means mounted on said diaphragm, and motor means for automatically establishing the distance between said switch contact means. 1
12. An alarm device as claimed in claim 11 wherein said motor means may be controlled by a second switch means in a remote location.
13. An alarm device as claimed in claim 11 which further comprises motor control means having circuit means for automatically establishing the distance between said first and second contacts and means for disconnecting said motor control circuitry. v
14. An alarm device asvclaimed in claim 13 which further comprises timingmeans automatically connecting and-disconnecting said motor control means at predetermined time intervals.
contact means at predetermined intervals.
' 10! k 1' i I.