WO1984002401A1

WO1984002401A1 - Water level monitor and/or alarm system for bilges

Info

Publication number: WO1984002401A1
Application number: PCT/AU1983/000187
Authority: WO
Inventors: Kevyn Barry Moore
Original assignee: Kevyn Barry Moore
Priority date: 1982-12-17
Filing date: 1983-12-19
Publication date: 1984-06-21
Also published as: EP0160646A1

Abstract

A water level monitoring and alarm circuit for the bilges of boats has two sets of probes (14, 15), (15, 16) which are contacted when the water bilges reach critical levels (A, B). The current flow through the probes (14, 15) switches on a timer (IC1) to operate a bilge pump (12) for a preset period to lower the water level. A by-pass circuit (Q2) retriggers the timer to continue operation of the pump (12) if the water has not fallen below level A. If the water level rises to level B, current flow through probes (15, 16) trip a timer (IC2) to operate an audible piezo alarm (PA) and visual alarm (LED1).

Description

Title: "WATER LEVEL MONITOR AND/OR ALARM SYSTEM FOR

BILGES" BACKGROUND OF THE INVENTION ( 1 ) Field of the Invention This invention relates to a water level monitor and/or alarm for boat bilges and other water containers. (2) Description of the Prior Art

Trawlers and other fishing boats, particularly those with wooden hulls, are liable to take on large amounts of water which collects in the bilges. If this water is not pumped overboard, the trawler or boat is liable to sink. This problem of taking on water occurs with all types of watercraft, even when at their moorings, as it is not possible to provide a perfectly water-tight hull. One area where waterleaks often occur is where the propellor shaft enters the hull.

In an attempt to overcome this problem, many boat owners have fitted bilge pumps to their boats, and these pumps are controlled by a switch which has a float means to monitor the level of the water in the bilges. This has only provided a partial solution to the problem. Firstly friction and stiction in the bushes mounting the float arm often leads to an incorrect float height, giving a false indication of the actual water level in the bilges. Secondly, as the boat is rocked in the water by the waves, the fluid level in the bilge may rise and fall, causing the float-operated switch to switch the bilge pump off and on e.g. every 2 to 3 seconds, quickly leading to damage of the pump. Certain electronic switch circuits have been tried but these have required complex triggering circuits which are prone to failure and which are also liable to cycle the pump on and off. In addition, the water in the bilges may come in contact with the electrical circuitry of the boat and be raised (or lowered) to the maximum positive (or negative) potential of the circuitry and so prevent the switches from operating.

SUMMARY OF THE PRESENT INVENTION It is an object of the present invention to provide an electronic monitor and/or alarm system which can monitor the water level in the bilges with good accuracy.

It is a preferred object to provide a system which can operate a bilge pump when the water level reaches a first critical level and then operate an alarm when the water level reaches a second more critical level.

It is a further preferred object to provide such a system where the probe or probes which contact the water can be placed remote from the remainder of the monitoring system e.g. to enable the electronic circuitry of the system e.g. to enable that part of the system to be positioned in a protected position.

It is a still further preferred object to provide such a system where the bilge pump is operated for a preset period and where, if the water level is still above the first critical level, the pump will be further operated for one or more preset periods until the water level falls below that critical level.

Other preferred objects will become apparent from the following description. In one aspect the present invention resides in an automatic bilge pump switch including: a set of probes adapted to be contacted by water at a critical level in the bilge; a switch means connected to the set of probes and adapted to be connected to a bilge pump; a power supply means adapted to be connected to the set of probes and/or the switch means; so arranged that when the water reaches the critical level; a current flow through the set of probes operates the switch means which operates the bilge pump to lower the water level below the critical level. Preferably the switch means includes a timer means which when switched on, causes the bilge pump to be operated for a preset period. Preferably, if the water level is still in contact with the probes, the timer means will be reset to cause the bilge pump to be operated for a further preset period or periods until the water level falls below the critical level. The switch means may include a power transistor interposed between the bilge pump and the power supply, the power transistor being switched on to switch on the pump.

In a second aspect the present invention resides in a water level alarm for bilges including :- a set of probes adapted to be contacted by water at a critical level in the bilge; an audible and/or visual alarm means connectable to a power supply; and switch means connected to the set of probes and to the alarm means so arranged that when the water level reaches the critical level, the alarm means is switched to indicate that the critical level has been exceeded.

The audible alarm means may include a piezo alarm, hooter or other suitable means. The visual alarm may include a LED (which may be a flashing LED), a neon tube or other suitable lamp. When a flashing LED is used, it may be connected across the audible alarm to modulate the latter. The set of probes may be mounted on the boxes containing the bilge pump switch and/or alarm or may be remote therefrom.

In a third aspect the present invention may reside in a combination of the bilge pump switch and alarm.

BRIEF DESCRIPTION OF THE DRAWINGS To enable the invention to be fully understood, a preferred embodiment will now be described with reference to the accompanying drawings, in which :- FIG. 1 is a schematic view of the system; and FIG. 2 is a schematic circuit diagram of the system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The system is provided in four main component groups - the set of probes 10, the pump switching and timing unit 11, the bilge pump 12 and the alarm unit 13. The system is powered by the boat's battery (not shown) which is connected to a positive rail V+ and earth.

The set of probes 10 has two outer probes 14, 15 with carbon tips at a first critical level A, when the pump 12 is to be switched on, and a central probe 16 with its carbon tip at a second critical level B, when the alarm 14 is operated.

When the water level rises and touches the tips of probes 14 and 15 at level A, current flows from earth, through current limiting resistor R19, to the probe 15, which is the negative supply probe. From probe 15, the current flows through the water to probe 14. The current then flows through resistor R1 to the base of PNP transistor Q1 where it overcomes the reverse bias on the transistor from the positive rail V+ via resistor R2 to switch the transistor Q1 on.

The transistor Q1 is switched on, current from the positive rail V+ flows through the emitter to the collectorof Q1 and then through resistor R3 connected to trigger pin 1 of an LM3905 monostable timer to start the timer cycle. The current also flows through diode D4 and resistor R6 to the base of NPN transistor Q2, overcoming the reverse bias supplied from earth to the base through resistor R7, turning transistor Q2 on. (The transistor Q2 and resistors R6, R7 act as a bypass circuit for the timer).

Simultaneously, current through diode D4 flows through resistor R20 to charge capacitor C10 to voltage V+ while the probes 14, 15 are in the water. Referring now to the timing circuit, timer IV1 , the timing circuit will be triggered when the voltage at pin 1 exceeds a preset threshold voltage of e.g. +1.6V and the timer will not retrigger if pin 1 is held high during the timing circuit but the timer will complete its timing cycle. Pin 2 is the voltage reference and is connected to an internal voltage regulator set at e.g. +3.15V while pin 3 has the timing resistors R4, R5 connected to pin 2 and the timing capacitors C1, C2 connected to earth. Pin 3 is connected to an internal comparator which, when the voltage across the timing capacitor reaches +2V, will change state to switch off the timing cycle. Pin 4 is connected to earth, as are the emitter pin 7 and logic pin 8 while pin 5 is connected to the positive rail V+ via protection diode D1 , transient currents being filtered out by capacitor C3. The collector/ output pin 6 is connected to the collector of transistor Q2 and to the collector of an internal NPN output transistor and the emitter pin 7 is connected to the emitter of the NPN output transistor and the base of transistor Q2 via resistor R7.

The logic pin 8 is connected to earth, switching on the output transistor during the timing period.

When the timber IC1 is triggered by the current flow to pin 1, capacitors. C1 and C2 start charging through resistors R4 and R5. When the votlage across capacitors C1 and C2 reaches 2 volts, the timing cycle will end, and if the water level has fallen below probes 14 and 15, causing transistor Q1 to turn off and allowing negative current to flow through R7 and R6 to pin 1 (thereby lowering the trigger voltage threshold) capacitors C1 and C2 will discharge.

The timing cycle cannot be retriggered unless the water has first fallen below the probes. For this reason, the previously mentioned bypass circuit is activated for as long as the water remains in contact with the probes. In the event of the water level not falling, the by-pass circuit will keep the rest of the circuit operating. During the timing cycle, pin 6 supplies negative current through resistor R9 to the base transistor of Q3, overcoming the positive reverse bias supplied by the positive rail through resistor R8, thereby turning transistor Q3 on. Negative current is also supplied to the base of transistor Q3 by the by-pass circuit, current flowing from earth to the emitter and then the collector of transistor Q2 to the base of transistor Q3. Capacitors C5 and C4 expedite the switching on and off of Q3, which is a PNP transistor. When Q3 switches on, positive current flows from the positive rail V+, to the emitter and the collector of Q3, then through resistor R10 to the base of transistor Q4, overcoming the reverse bias supplied from earth, through resistor R11. Capacitors C6 and C7 expedite the switching on and off of transistors Q4, which is an NPN power transistor. When transistor Q4 turns on, current flows from earth, to the emitter and then the collector of transistor Q4, to the bilge pump 12, and returns to the positive rail V+, thereby turning on the bilge pump. After the timing period, and if the water level has fallen, all forward bias to Q1 , Q2, Q3 and Q4 is switched off and reverse bias is applied to these transistors turning them off. Diode D2 is to protect Q4 from back E.M.F. generated by the windings of the bilge pump when transistor Q4 turns off, while diode D1 is to protect the printed circuit board circuitry from reverse polarity and capacitor C3 is a decoupling capacitor to prevent false triggering of the timing circuit by voltage spikes in the power supply. If the water level rises to contact probe P2 (the second critical level B), current will flow from earth, through limiting resistor R19 to the negative supply probe 14. From there, the current flows through the water, through probe 16 and resistor R12 to the base of transistor Q5, overcoming the reverse bias supplied from the positive rail V+ through resistor R13, thereby switching transistor Q5 on, where Q5 is a PNP transistor. When transistor Q5 is switched on, current flows from the positive rail V+ to the emitter and then the collector of transistor Q5, then through resistor R14 to the base of transistor Q6, overcoming the reverse bias supplied from earth, through transistor R15, thereby switching Q6 on, where Q6 is an NPN transistor.

When transistor Q6 switches on, negative current flows from earth to the emitter and then the collector of transistor Q6 and to the common connection of the 7812 12 volt voltage regulator. Transistor Q6 also provides a negative current path for the pulsing circuit, consisting of IC2 and associated circuitry, and to the piezo alarm P.A. and visual alarm LED1. Positive current at 24 volts flows to the In terminal of the 7812 and current at 12 volts out of the OUT terminal of the &812.

The pulsing circuit, LED1 and the piezo alarm operate on 12 volts. The pulsing circuit IC2 as shown in FIG. 2 is a 555 timer wired for a stable operation with the following pin functions -

1. Earth

2. Trigger

3. Output 4. Reset

5. V+

6. Discharge

7. Threshold

8. Control Voltage. Upon startup, the voltage across C8 is low, which causes the timer to be triggered via pin 2. This forces the output high turning off the discharge transistor and provides a current path for charging capacitor C8 via resistors R16 and R17. Capacitor C8 then charges towards V+ until the voltage reaches 2/3V+, which is the upper threshold. The output then goes low and capacitor C8 begins to discharge towards earth via resistor R17 until its voltage reaches 1/3V+, which is the lower trigger point. This will trigger the timer again and begin a new cycle. The timer will then continue to oscillate between 2/3V+ and 1/3V+ threshold levels.

Whilst the output of IC2 is high, positive current will flow from pin 3 through LED 1 and the piezo alarm to ground through transistor Q6. This will cause LED 1 and the piezo alarm to operate until the output of IC2 goes low, LED 1 and piezo alarm will be turned off. Output timing:

T1 (output high) = 0693 (R16+R17) C8 T2 (output low) + 0693 R17 C8 If the water level drops below probe 16 negative current will cease to flow to the base of transistor Q5 which will then switch off. This will then cause transistor Q6 to switch off thereby preventing negative current flow from the rest of the alarm circuit. The alarm circuit then ceases to operate.

If the whole unit is designed for a 12 volt electrical system, the 7812 voltage regulator is not necessary. The 555 timer IC has a maximum voltage rating of 18V and the pulsing circuit may be deleted if desired. In the event of failure of the timer, or if the water level has not dropped below the probes, the back-up circuit, incorporating transistor Q2, will keep the bilge pump operating as the LM3905 timer will not retrigger until the water level drops below the probes to allow Q1 to turn off. However, when the water level falls below the probes, capacitor C10 which has been charged to voltage V+ discharges through resistors R20, R6, overcoming the reverse bias of resistor R7, to maintain the transistor Q2 switched on for a period determined by the values of resistors R20, R6 and capacitor C10 which should not be less than the minimum safe pumping time of the bilge pump.

The timer will not retrigger IC1 until the input at pin 1 is lowered below the threshold voltage and the diode D4 prevents negative current flow to the pin. Therefore resistor R21 connected to earth provides a suitable path to enable pin 1 to fall to earth. Diode D4 prevents capacitor C10 from discharging through resistors R3, R21 and resistor R20 is a current limiting resistor. In a modified circuit (not shown) timer LM3905 may be replaced by a 555 timer which will retrigger automatically while current is supplied to the trigger pin by transistor Q1 , the back up circuit incorporating transistor Q2 again being used. It is not essential that the tips of the probes

14-16 be of carbon as little electrolysis damage is likely to occur. However, it is preferred that the tips come to a point to better penetrate any oil layer on top of the bilge water. The probes 14-16 may comprise lengths of brass rod sheathed in plastic or rubber, with only their tops exposed. The sheathing prevents moisture on the housing 18 for the switching and timing unit 11 tripping the probes which are high sensitive. The housing 18 may incorporate one or more heat sinks 19 to dissipate the heat generated in power transistor Q6.

The switching and timing unit 11 may be mounted in the bilges and the alarm unit 13 in the cockpit. However, in certain applications, it may be preferred to employ remote probes 10 with both units 11,13 in the cockpit.

It will be readily apparent to the skilled addressee that the choice of the particular components will be determined by, inter alia, the voltage and polarity of the power supply and the current drawn by the bilge pump . It will also be apparent that the power transistor Q6 may be replaced by a relay which controls the current to the bilge pump 12.

In certain applications, only the bilge pump switching unit or the alarm unit will be required.

Various changes and modifications may be made to the embodiment described without departing from the scope of the present invention. For example, the invention may be used to monitor the level of water or other conducting liquids in other containers e.g. such as overflow tanks for engine cooling system.

Claims

CLAIMS:

1. An automatic bilge pump switch including: a set of probes adapted to be contacted by water at a critical level in the bilge; a switch means connected to the set of probes and adapted to be connected to a bilge pump; a power supply means adapted to be connected to the set of probes and/or the switch means; so arranged that when the water reaches the critical level, a current flow through the set of probes operates the switch means which operates the bilge pump to lower the water level below the critical level.

2. A switch as claimed in Claim 1 wherein the switch means includes : a timer means which, when switched on, cause the bilge pump to be operated for a preset period and which will be retriggered if the water is still in contact with the probes to cause the bilge pump to be operated for a further preset period or periods until the water level falls below the probes.

3. A switch as claimed in Claim 2 wherein: the switch means further includes a power transistor interposed between the bilge pump and the power supply, the power transistor being switched on to switch on the pump .

4. A switch as claimed in Claim 2 or Claim 3 and further including: a by-pass circuit to switch on the bilge pump when the water is in contact with the probes but the timer is not switched on, the by-pass circuit being arranged to operate the pump for a preset minimum time after the water level has fallen below the probes.

5. A switch as claimed in Claim 4 wherein: the by-pass circuit includes a capacitor which is charged when the water is in contact with the probes and which is discharged to maintain the by-pass circuit switched on for the preset period.

6. A water level monitoring and control system for bilges including: a bilge pump connected to an electrical power supply in a vessel; and a pump switch as claimed in any one of Claims 1 to 5, so arranged that the bilge pump is switched on when the water level in the bilges contacts the probes.

7. A system as claimed in Claim 6 and further including: a second set of probes to be contacted by the water at a second critical level; an audible and/or visual alarm connectable to the electrical power supply; and alarm switching means operable to operate the alarm when the water level contacts the second set of probes.

8. A system as claimed in Claim 7 wherein: the switch means includes a timing circuit to operate the alarm for a preset period after the water contact the second set of probes and the timing means being retriggered until the water level falls below the second set of probes.

9. An automatic bilge switch substantially as hereinbefore described with reference to the accompanying drawings.

10. A water level monitoring and control system for bilges substantially as hereinbefore described with reference to the accompanying drawings.