GB2354098A - Overflow or leak detector arrangement for domestic appliance - Google Patents

Abstract

An overflow or leak detector for a domestic appliance, eg. a washing machine (WM) comprises an external sensor (M), which may be a resistance sensor, for detecting overflow form the appliance, wireless transmitter means (TX), which may be an acoustic, radio or infra-red transmitter, coupled to the sensor and wireless receiver means (RX) coupled to external switching means which, on detection of liquid by the sensor, cuts off power and/or water to the appliance, or pumps water out of the appliance. Also described is a sensor which is preferably in the form of a mat consisting of upper and lower wire mesh electrodes separated by an insulating spacer grid and is permeable to water collecting on the floor.

Description

2354098 Overflow/leak detector arrangement The present invention relates

to an arrangement for detecting overflow or leakage of water, particularly from a washing appliance eg a clothes washing machine or a washer/drier, or a dishwasher. If such overflow or leak occurs, eg as a result of a malfunction of the appliance, and is undetected, not only can the room in which the appliance is located suffer water damage, but also any rooms below, eg in a block of flats.

Such detection arrangements are known, eg from GB 2,272,553A, GB 2,266, 396A, GB 2,184749A and US 3,770,002. However these arrangements cannot easily be retro-fitted by the consumer because they require a hard-wired electrical connection to the internal circuitry of the appliance or to the mains wiring. In my co-pending patent application GB 2,329,501A an arrangement utilising a plug-in circuit breaker to disconnect power to the appliance is disclosed, thereby overcoming the above disadvantage.

Nevertheless there is a need for an improved arrangement in which the installation can be carried out by any consumer and preferably avoids the need for any tools or specialist skills. In particular it has been found that the restricted and often inaccessible space around the back of a washing machine can make installation difficult.

Accordingly, in one aspect the present invention provides an overflow/leakage detector arrangement for a domestic appliance, the arrangement comprising an external sensor for detecting overflow from the appliance, wireless transmitter means coupled to the sensor and wireless receiver means coupled to external switching means whereby in use, power and/or water to the appliance are cut off or water is pumped out of the appliance in response to detected overflowfleakage.

The transmitter and receiver means can for example be a radio transmitter and receiver, but other arrangements can also be employed, utilising eg infra- red or ultrasonic communication. The invention simplifies installation by eliminating the wiring in the vicinity of the appliance, and has a further advantage of a perceived improvement in safety, because the sensor of the overflow (typically a resistance sensor located on the floor so as to be wetted by overflowing water) need not be 2 connected to any mains circuitry.

Preferably the external switching means comprises a plug-in mains adaptor having a socket for a mains plug of the appliance and is arranged to cut off power to the appliance in response to detected overflow. This preferred feature simplifies installation by eliminating the requirement for hard wiring between the switching means and the appliance.

In one embodiment the mains adaptor is connected to the wireless receiver means by a lead which in use enables the position and/or orientation of the receiver means to be varied. This preferred feature enables the communication path between the transmitter and receiver to be optimised even if the mains socket to which the appliance is connected (and hence the sensor) is obscured from the appliance.

The invention also provides an appliance in combination with an overflow/leakage detector arrangement in accordance with the invention as defined above, the overflow/leakage detector arrangement being arranged to cut off water and/or power to the appliance or to pump out water from the appliance in response to detected overflow.

In another aspect the invention provides a detector of escaped water comprising an 2-5 assembly of two water-permeable electrodes each in sheet or strip form and insulating water-permeable spacer means arranged to separate the electrodes, the electrodes being coupled to resistance sensing means, the assembly being capable of resting at floor level and being wetted by water at floor level. The escaped water can be from any source, eg a leaking storage tank or a leaking or burst pipe.

Preferably at least one of the electrodes is in the form of a grid or mesh.

In a preferred embodiment the resistance sensing means is coupled to a wireless transmitter.

Preferably the resistance sensing means is arranged to conduct resistance measurements with current flow reversed. This avoids errors due to electrolytic action.

3 Preferred features of the invention are defined in the dependent claims.

A preferred embodiment of the invention is described below by way of example only with reference to Figures 1 to 5 of the accompanying drawings, wherein:

Figure I is a somewhat schematic front elevation of a clothes washing machine provided with an overflow detector arrangement in accordance with the invention; Figure 1A is a schematic side elevation showing the front of the resistive sensor and 10 associated transmitter utilised in the arrangement of Figure 1; Figure 2 is an exploded view of the resistive sensor utilised in the arrangement of Figure 1; 15 Figure 3 is a circuit diagram of the transmitter module utilised in the arrangement of Figure 1; 20 Figure 4 is a timing diagram showing the states of the resistance sensor ports of the transmitter module of Figure 3; Figure 5 is a plot of resistance:time as sensed by the resistance sensor, showing the 25 generation of an alarm condition, and Figure 6 is a circuit diagram of the receiver module utilised in the arrangement of FIgure 1. 30 Referring to Figure 1, a clothes washing machine (which will subsequently be referred to simply as a washing machine) WM having a conventional mains lead LD and conventional three-pin mains plug P2 is shown. This would normally be plugged in to a wall socket. In this embodiment the washing machine is unmodified 35 but is protected against the consequences of overflow by a sensor mat M connected to a transmitter module TX and lying on the floor immediately beneath the washing machine, and by a receiver module RX including a mains socket into which plug P2 is plugged, the receiver module having a captive mains lead terminating in a 40 conventional three-pin mains plug PI which is plugged into a mains socket 4 The transmitter module TX (whose body portion is suitably located at and extends along one edge eg the front edge of mat M) is powered by a 9V battery and includes a miniature loop antenna A2 which transmits FM radio signals to a similar loop antenna A 1 in the receiver module RX. As will be described in more detail below, in the event of an overflow the sensor mat M is wetted, its detected resistance falls, and a signal is transmitted by the transmitter module which causes the receiver module to break the mains circuit connection in the socket receiving plug P2, thereby cutting off power to the washing machine and preventing flooding, since the inlet solenoids of the washing machine (which control water flow to the appliance) close automatically when mains power is cut. A green LED D5 indicates that the sensed resistance is within normal range (ie there is no overflow) and a red LED gives a low battery warning.

As shown in Figure JA, the body portion of the transmitter module TX has an rearwardly inclined face FC which faces and lies closely adjacent the lower front edge of the washing machine WM, so as to guide any water which leaks or overflows from the front of the washing machine onto the ma t M, even if the floor is sloping downwardly towards the front of the washing machine. Preferably the mat M extends rearwardly beyond the lower rear edge of the washing machine so as to catch any water which escapes from the rear.

Referring to Figure 2, the sensor mat M comprises an upper grid electrode El of wire mesh and a similar lower grid electrode E2 also of wire mesh, the electrodes being separated by a spacer grid SP of insulating material, eg polypropylene netting.

The resulting mat assembly is highly permeable to, and is therefore immediately wetted by, any water escaping from the washing maching WM and its resistance decreases substantially as a result, eg from many megohms to a few kilohms or even a few tens of ohms if the water has a high ionic content.

The sensor and transmitting circuitry associated with mat M is shown in Figure 3.

This circuitry is highly miniaturised and is entirely located within transmitter module TX shown in Figure 1. Referring to Figure 3, the circuitry basically comprises a hybrid 418MHz FM transmitter IC1 (RS, part No 740-297) having a miniature loop antenna A2 and controlled by ports PS and P6 of a BASIC STAMP 2 PIC controller IC2, the latter also acting as the voltage source and timer of a resistance sensor at ports 8 to 15. PIC controller IC2 is provided with EEPROM which has been previously programmed via pins I to 3 from a PC (not shown).

The hybrid FM transmitter ICI has its data pin connected to the collector of a switching transistor Q1 which is controlled by a data output port P5 of IC2 via a resistor R16. The 418MHz carrier is generated by an output port P6 of IC2 going HIGH to switch on a switching transistor Q2 via a base resistor R17, pulling down the collector of Q2 to zero volts (the level of the ground rail connected to the negative terminal of battery B, to pin 23 of IC2 and the emitters of Q I and Q2) and hence the vss pin of transmitter ICL The collector of Q1 is connected to the 9V supply rail by a collector resistor R9.

The circuitry is powered by a 9V PP9 battery B via a reset switch SW and is arranged to test the battery voltage while the FM transmitter IC1 is activated. To this end, port P3 is coupled to a 5V rail via a Zener diode (which provides a defined voltage drop) and a pre-set potentiometer VR, and is periodically set to input mode.

If its sensed voltage decays below about 1.4V(as a result of the battery voltage being too low for reliable operation) its state switches from HIGH to LOW and a red LED D6 (connected in series with a current-limiting resistor R5 to the 9V rail) is switched ON by pulling down (normally HIGH) port P1 to give a low battery warning.

Green LED D5 in series with current limiting resistor between the 5V rail and port PO is controlled by this port (in the LOW state) and lights up when the resistance of the mat M as sensed by the sensor is in the normal range, ie not indicative of wetting caused by overflow from the washing machine.

Ports P4 and P7 are spare and are connected to the OV (ground) rail by resistors R15 and R18 respectively.

The sensor portion of the circuitry includes plastic film timing capacitors C1 and C2 which are connected in series with the electrodes El and E2 (Figure 2) of the sensor mat M. The free end of capacitor Cl is connected to paralleled resistors R13 and R14 and thence to ports P8 and P9 of IC2 and the free end of capacitor C2 is similarly connected to paralleled resistors R 9 and R 10 and hence ports P15 and P14 respectively. The junction of capacitor C1 and its associated mat electrode is connected via paralleled resistors R12 and R3 to ports P10 and P1 I respectively and the junction of capacitor C2 and its associated other mat electrode is connected via 6 paralleled resistors R1 1 and R2 to ports P12 and P13 of IC2 respectively. Paralleled pairs of resistors are used in conjunction with pairs of ports in order to reduce the effect of internal resistances in IC2 and thereby increase the measurement range and/or accuracy.

The operation of the above sensor arrangement will now be described with reference to Figure 4. Initially, all of ports P8 to P15 are set HIGH for 300 ms (resulting in low impedance connections between them in IC2) to discharge CI and C2. At T1, ports 8 to I I go LOW, causing C2 to be charged via R9 and RIO and the sensor mat 10 M. Simultaneously, ports 12 and 13 are set to INPUT mode, sensing the voltage at the junction of C2 and its associated sensor mat electrode EI/E2. The time taken for this sensed voltage to fall sufficiently to switch ports 12 and 13 to the LOW state is measured and at this instant (T2) charging of C2 ceases. 15 From T2 to T3, all ports 8 to 15 are set HIGH again to discharge C2. At time T3, ports 12 to 15 go LOW, causing CI to be charged via R13 and R14 and 20 the sensor mat M. Simultaneously, ports 10 and I I are set to INPUT mode, sensing the voltage at the junction ofCI and its associated sensor mat electrode EVEL The time taken for this sensed voltage to fall sufficently to switch ports 10 and I I to the LOW state is measured and at this instant (T4) charging of CI ceases. 25 It will be noted that the current passes in opposite directions through the sensor mat M during the above phases of the measurement cycle (involving charging of capacitor C2 and capacitor CI respectively). The measured periods TI-T2 and T3T4, which increase with resistance of the mat M, are indicative of resistance in 30 opposite directions and are averaged in order to eliminate errors due to diode effects and possibly stray voltages due to electrolytic action. The above sensing cycle is repeated approximately every ten seconds under the 35 control of controller IC2. A plot of mat resistance:time is shown in Figure 5. The resistance measurements are obtained discontinuously and are shown as values THI to TH4. It should be bome in 40 mind that each resistance value shown is in fact the average of two resistance values obtained in the above-described phases of the measurement cycle by taking 7 measurements with current flow in opposite directions.

An adaptive sensing regime is followed by utilising these resistance values TH1 to TH4 as successive threshold values and calculating the difference in resistance between successive threshold values, as shown by the vertical arrows in Figure 5. If the drop in resitance exceeds a certain predetermined value (as it does between THI and TH2) an alarm condition is generated and the transmitter module IC1 is instructed to transmit an alarm signal to the receiver module RX.

The gradual rise in resistance around TH3 and TH4 is caused by the mat M drying out. The gradual fall in resistance before TH1 could be caused by an increase in humidity for example. The circuitry is immune to such conditions because they manifest themselves as a very gradual fall in resistance which does not lead to substantial drops in resistance between successive measurements.

The receiver module RX (Figure 1) will now be described in detail with reference to Figure 6. The circuitry consists essentially of a 418MHz hybrid FM receiver IC3 (RS part No 740-304) coupled to port PO of a hybrid PIC microcontroller IC4, which has been previously programmed via pins I to 3 thereof. This controls a normally open mains relay RYvia paralleled ports P8 to P15 which are connected by a resistor R19 to the base of a switching transistor Q3 (suitably a TIP31C switching transistor) whose emitter and collector are in series with the relay winding, thereby controlling the mains connection between plug P1 and the socket into which plug P2 is fitted (Figure 1).

The receiver module operates on the relay RYon a toggling basis, ie unless and until a preset signal is received by the hybrid FM receiver IC3, the relay RY remains in the condition in which it was last set by the controller IC4.

The arrangement is powered by a step-down transformer TR whose primary is permanently connected across the live and neutral wires from plug PI and whose secondary is connected to a bridge rectifier BR. The output of rectifier BR is smoothed by capacitors CIO and C20 and feeds the series combination of the relay coil and the emitter and collector of Q3.

A buzzer BZ is connected between port P7 and the +5V rail Vss.

The transmitter TX is energised by any one of the following conditions:

1. A transmission is made soon after power-on to communicate start-up conditions to the receiver. These include a starting level of conduction of the sensor mat M which is recorded by the receiver RX for comparison purposes. Provided the conduction of the mat is within measuring range, such a transmission causes the receiver to stop sounding the alarm and it causes it to connect power to the washing machine WM.

2. A transmission is made whenever the sensing times fall by more than 10% relative to the start-up times. Such a transmission includes the new sensor time measurement which will be compared with the start-up level by the receiver RX. In most instances, the receiver will, as a result of this comparison, sound the wet alarm BZ and isolate the washing machine.

3. A transmission is commanded by a watchdog timer if no other transmission has been made for a period of approximately 30 minutes. This proves the integrity of the radio link and resets a corresponding alarm watchdog timer in the receiver RX.

Such a transmission includes the new sensor time measurement which will be compared with the start-up level by the receiver but, in most cases, this will be at a level that does not qualify for an alarm.

4. A transmission is made in the event that the sensed resistance falls below a predermined minimum. This feature ensures that a very slow leak which would otherwise not be detected (as a result of failing to cause the 10% fall in sensing time referred to in item 2 above) triggers an alarm. 30 5. A special "low voltage" transmission is made if, during a transmission, the battery voltage falls below the pre-set threshold. The "low voltage" transmission includes a special code that causes the receiver to sound the alarm periodically but it will not 35 isolate the washing machine.

The transmissions consist of a sequence that is repeated three times and consists of a unique numeric signature code and a data string.

The signature code must be agreed between the transmitter TX and receiver RX. This may be done by arranging dip switches on either the receiver or transmitter to 9 conform to the transmitter's or receiver's signature. Alternatively, both may be manufactured with the same signature codes and sold only in pairs.

The component values in the described embodiment are as follows:

Cl. 1.1 microfarads Rio 110 ohms C2 1.1 n-ficrofarads R11 110 ohms VR1 100 kilohms R12 110 ohms R2 110 ohms R13 110 ohms R3 110 ohms R14 110 ohms R4 500 ohms R15 10 kilohms R5 500 ohms R16 68 kilohms R8 10 kilohms R17 68 kilohms R9 110 ohms R18 10 kilohms, R19 1 kilohm In other embodiments the receiver could be arranged, in response to an alarm condition, to energise a pump which would pump out water and/or to actuate a solenoid valve which would cut off the water supply to the washing machine (as in my co-pending patent application GB 2,329,501A).

In embodiments in accordance with the second aspect of the invention the sensor mat M can be used to detect escaped water from a source other than a washing machine or other appliance - for example from a storage tank.

Claims (1)

1. Claims

   1. An overflow/leakage detector arrangement for a domestic appliance, the arrangement comprising an external sensor for detecting overflow from the appliance, wireless transmitter means coupled to the sensor and wireless receiver means coupled to extemal switching means whereby in use, power and/or water to the appliance are cut off or water is pumped out of the appliance in response to detected overflow/leakage.

   2. An overflow/leakage detector arrangement according to claim I wherein the external switching means comprises a plug-in mains adaptor having a socket for a mains plug of the appliance and is arranged to cut off power to the appliance in response to detected overflow/leakage.

   3. An overflow/leakage detector arrangement according to claim 2 wherein the mains adaptor is connected to the wireless receiver means by a lead which in use enables the position and/or orientation of the receiver means to be varied.

   4. An overflow/leakage detector arrangement according to any preceding claim wherein the external sensor is a resistance sensor provided with electrode means which in use are exposed to water which has escaped from the appliance.

   5. An overflow/leakage detector arrangement according to claim 4 wherein the external sensor is arTanged to perform repeated resistance measurements and to generate a control signal on the basis of a comparison between successive resistance measurements.

   6. An overflow/leakage detector arrangement according to claim 5 wherein the external sensor is arranged to update the threshold value and to perform the comparison with the updated threshold value, thereby allowing for drift in the threshold value due to changing ambient conditions.

   7. An overflow/leakage detector arrangement according to any of claims 4 to 6 wherein the resistance sensor is arranged to reverse the current flow associated with resistance measurements.

   11 8. An overflow/leakage detector arrangement according to any of claims 4 to 7 wherein the electrode means are water-permeable and are spaced apart by an insulating spacer which retains moisture in the space between them.

   9. An overflow/leakage detector arrangement according to any of claims 4 to 8 wherein the electrode means are in the form of a mesh or grid. 10. An overflow/leakage detector arrangement according to any preceding claim 10 wherein the wireless transmitter means and wireless receiver means are, respectively, a radio transmitter and receiver. 11. An overflow/leakage detector arrangement according to any of claims I to 9 15 wherein the wireless transmitter means and wireless receiver means are, respectively, an ultrasonic transmitter and receiver. 12. An overflow/leakage detector arrangment according to any of claims 1 to 9 20 wherein the wireless transmitter means and wireless receiver means are, respectively, an infrared transmitter and receiver. 13. An appliance in combination with an overflow/leakage detector arrangement as 25 claimed in any preceding claim, the overflow detector arrangement being arranged to cut off water and/or power to the appliance or to pump out water from the appliance in response to detected overflow. 14. An appliance and overflow/leakage detector combination as claimed in claim 13 30 wherein the appliance is a clothes washing machine. 15. A detector of escaped water comprising an assembly of two water-permeable electrodes each in sheet or strip form and insulating water-permeable spacer means 35 arranged to separate the electrodes, the electrodes being coupled to resistance sensing means, the assembly being capable of resting at floor level and being wetted by water at floor level. 40 16. A detector as claimed in claim 15 wherein the at least one of the electrodes is in the form of a conductive grid or mesh.

   12 17. A detector as claimed in claim 15 or claim 16 wherein the resistance sensing means is coupled to a wireless transmitter.

   18. A detector as claimed in any of claims 15 to 17 wherein the resistance sensing means is arranged to conduct resistance measurements with current flow reversed.

   19. A detector of escaped water substantially as described hereinabove with reference to Figure 2 optionally in conjunction with Figures 3, 4 and 5 of the accompanying drawings.

   20. An overflow detector arrangement substantially as described hereinabove with reference to Figures I to 6 of the accompanying drawings.

   21. An appliance and overflow detector combination substantially as described hereibabove with reference to Figures Ito 6 of the accompanying drawings.