GB2235801A

GB2235801A - Leak detection and warning system

Info

Publication number: GB2235801A
Application number: GB8920258A
Authority: GB
Inventors: David Stanley Bottomley; John Epps
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-09-07
Filing date: 1989-09-07
Publication date: 1991-03-13
Also published as: GB8920258D0

Abstract

The system comprises a sensor 3 to detect presence of a liquid electrolyte, and a transmitter 6 connected thereto to transmit a signal at least intermittently unless the sensor indicates the presence of a liquid electrolyte, in which case said signal is inhibited. The sensor and transmitter are powered by battery power. A detector/receiver 8 detects said signal and, in response to an absence of signal within a predetermined time period, causes a relay 11 to open a switch in a mains electrical power supply eg for a washing machine or electric blanket. The mains power supply also powers said receiver/detector but is electrically isolated from the transmitter and other means powered by said battery. <IMAGE>

Description

LEAK DETECTION AND WARNING SYSTEM The present invention relates to a leak detection, warning and isolation system. More particularly, but not exclusively, it relates to such a system for use with electrically powered washing machines.

The term "washing machines" is intended herein to include not only clothes washing machines but dish washing machines and indeed any electrically powered machine which contains conductive fluid. Other faults could be detected by transducer changes and the benefits of fail-safe intrinsic safety offered by this system used in any number of applications.

It is a fact that, occasionally, washing machines may leak and allow the water which should be contained therein to flow onto the floor beneath them. This may not always be detected immediately and, in some instances, a great quantity of water may escape before detection occurs.

The ensuing flood may be inconvenient and possibly hazardous or destructive; also the water, which is an electrolyte, may penetrate electrical circuits in the building potentially causing further hazards and damage.

It would be possible to detect a flood by providing a conductive sensor beneath the machine and causing any such detection to break the power supply to the machine, which should prevent further water entering if the machine is equipped with electrically operated valves. However, this is not necessarily an advantage if it requires an electrical connection between the electric power mains and the water because this can be dangerous. Similarly, hazards can exist if the sensor device is not isolated, for all practical terms, from the electrical power mains.

It is an object of the present invention to provide a leak detection, warning and fault isolation system which enables separation of the electrical power supply to the machine and a leakage sensing device.

According to the present invention there is provided a leak detection and warning system comprising sensor means to detect presence of a fluid possessing the property of electric conduction, transmitter means connected to said sensor means to transmit a signal at least intermittently unless said sensor means indicates the presence of a conducting fluid, in which case said signal is inhibited, battery power means to power said sensor and transmitter means, detector/receiver means to detect said signal and, in response to an absence of signal within a predetermined time period, to cause a relay means to open a switch in a mains electrical power supply for a washing machine, said mains power supply also powering said receiver/detector means but being electrically isolated from said transmitter means and other means powered by said battery means.

The means to isolate said mains power supply may comprise a signal emitted by e.g. an IED signalled by the battery power transmitter means and e.g. a photoelectric cell receiving said emitted signal and signalling said mains powered detector/receiver.

The isolation means may alternatively comprise an acoustic signal between e.g. a loudspeaker and e.g. a microphone.

Preferably said detector/receiver means additionally initiates an alarm in the absence of signal within the predetermined time period.

The alarm may be powered by said mains power supply.

The alarm may be visual and/or acoustic.

A second alarm, powered by said battery means, may be provided to be actuated when said sensor means detects the presence of a fluid.

Said second alarm may be visual and/or acoustic.

There may also be provided detector means to indicate when the battery power means is unreliable, said detector means initiating said second alarm.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawing, the single figure of which shows schematically a circuit diagram of the system.

The system comprises essentially two units, a battery powered sensor unit 1 and a AC mains powered switching unit 2.

The sensor unit comprises a moulded plastics material box and has detection electrodes protruding through the case. The presence of water (in this application of the system) is detected when the resistance between the two electrodes falls below a preset value, and in this case, a signal is given to a switching device 4.

The switching device 4 includes a semi-conductor amplifier and, when stimulated by the falling resistance of the sensor 3, signals when the resistance reaches a switching threshold, which may be predetermined. 'The switching device incorporates a hysteresis feature which ensures clean switching, whilst preventing intermittent alarm conditions in borderline cases, e.g. as wetting of the sensor commences with say, a fluid of variable conductivity. The signal from the switching device passes in one case to an alarm 5, which in a preferred embodiment comprises a semi-conductor oscillator with a piezo electric acoustic transducer. The system includes a battery saving feature and the acoustic cavity is resonant at the transducer frequency.

A signal is also sent from a switching device 4 to a transmitter 6 which normally operates intermittently on a low duty cycle to preserve battery power, but on receipt of the signal will cease transmitting.

Finally in the sensor unit 1, there is provided a low battery detector 7. When the battery which powers the unit 1 is approaching exhaustion, the small variations of normal circuit current result in a crossing of the supply threshold for reliable operation. To avoid intermittent operation and hence user confusion regarding reliability, the battery unit is equipped with a sensing circuit which sounds the audible alarm 5. This alarm 5 can only be overcome by disconnection and replacement of the battery.

As an alternative to the acoustic alarm 5, a visual alarm may be provided or indeed, the two may be combined.

The mains powered switching unit 2 comprises a switching box having a standard 13 amp male plug assembly 10 and a 13 amp socket assembly 12. It may thus be connected in the normal manner into a 13 amp mains supply socket, and can accept a standard 13 amp plug wired to the washing machine. Power is fed from the plug to the socket through a power switch 11 which also powers a detector/receiver 8 and an alarm 13.

In normal use, the detector receives intermittent signals from the transmitter, detects them and passes them to the receiver and switch which act to hold on a relay maintaining the power switch 11 closed. If no signal is received from the transmitter after a predetermined period of time, the switch signals the alarm 13, which may be acoustic and/or visual, and also deactivates the relay causing the power switch to open and cut off the supply to the washing machine. A reset button may be provided in the power switch 11 to initiate power supply once the problem has been resolved.

It is an important feature of the present invention that there is no electrical connection between the electrical power supply mains and the battery powered sensor. This may be achieved in one of several ways. For example, the transmitter may emit an acoustic signal and the detector may comprise a microphone or other acoustic receiver, engineered to prevent false alarms from extraneous sources. In this case, the transmitter 6 and detector/receiver 8 may be physically separate one from the other.

Alternatively, the transmitter may emit energy within the electromagnetic spectrum, for example a light beam, an infra-red beam or a microwave beam, which radiation is detected by the detector/receiver 8 and acted upon. Again, the transmitter 6 and detector 8 need not be immediately adjacent, but could require substantially direct line of sight, depending on the specific application of the system.

One further preferred alternative is to connect the transmitter 6 with the detector 8 by means of a pair of wires activating an LED within or immediately adjacent to the detector 8 but powered by the battery. The detector 8 comprises an optically isolated silicon switch or the like which signals on the intermittent illumination of the LED.

In this case, the battery powered sensor unit 1 and the AC mains powered switching unit 2 are connected by electrical connectors, but these are only small capacity wires adapted to carry direct voltage battery power to the LED housed within the detector 8. For convenience, these wires may be connected at one or both ends by means of a jackplug and socket arrangement or the like.

Other means of providing an electrically isolating interface between the mains powered detector/receiver 8 and the transmitter 6 may be envisaged.

Other uses of the system can be foreseen. For example, the "washing machine" may be an electric blanket in a bed, which would be disconnected as soon as the bed became wet and there are any number of industrial applications, where the battery unit 1 offers the benefit of intrinsic safety.

Claims

CLAIMS:

1. A leak detection and warning system comprising sensor means to detect presence of a liquid electrolyte, transmitter means connected to said sensor means to transmit a signal at least intermittently unless said sensor means indicates the presence of a liquid electroyte, in which case said signal is inhibited, battery power means to power said sensor and transmitter means, detector/receiver means to detect said signal and, in response to an absence within a predetermined time period, to cause a relay means to open a switch in a mains electrical power supply for a washing machine, said mains power supply also powering said receiver/detector means but being electrically isolated from said transmitter means and other means powered by said battery means.

2. A system as claimed in claim 1, wherein the means to isolate said mains power supply comprises a visual signal emitted by a light source, e.g. an LED, signalled by the battery power transmitter means and a light receiver, e.g. a photoelectric cell, signalling said mains powered detector/receiver.

3, A system as claimed in claim 1, wherein the isolation means comprises an acoustic signal between an acoustic source, e.g. a loudspeaker, and an acoustic detector, e.g. a microphone.

4. A system as claimed in any one of the preceding claims, wherein said detector/receiver means additionally initiates an alarm in the absence of signal within the predetermined time period.

5. A system as claimed in claim 4, wherein the alarm is powered by said mains power supply.

6. A system as claimed in either claim 4 or claim 5, wherein the alarm is visual and/or acoustic.

7. A system as claimed in any one of the preceding claims, wherein a second alarm, powered by said battery means, is provided to be actuated when said sensor means detects the presence of a liquid electrolyte.

8. A system as claimed in claim 7, wherein said second alarm is visual and/or acoustic.

9. A system as claimed in claim 8, further comprising detector means to indicate when the battery power means is unreliable, said detector means initiating said second alarm.

10. A leak detection and warning system substantially as described herein with reference to the accompanying drawings.