GB2186722A - Detecting leakage of liquid from machines - Google Patents

Abstract

The present invention comprises circuitry in combination with a liquid sensor element (Figs. 2 to 5) positioned externally to a protected appliance, so as to receive liquid leaking therefrom, and thereby providing an alarm and/or a safety response. The circuitry comprises two liquid detection circuits, the first activating an alarm B1 in the event of a small leakage. The second circuit activates a visual warning LED 1 and a relay RL1 in the event of a large leakage, thereby electrically disconnecting the protected appliance. The sensor element comprises mutually spaced electrode members (10, 11, 12; 20, 21, 22) provided in contact with a porous material (7, 8; 17), for receiving the liquid to be detected, the said liquid providing an electrical connection between the said electrode members. Electrical connection between a pair of electrode members closes the first electrical circuit to activate the alarm. Electrical connection between one of these electrode members and a further electrode member activates the visual warning and the relay which causes electrical disconnection of the appliance. <IMAGE>

Description

SPECIFICATION Detecting leakage of liquids from machines The present invention relates to detecting leakage of liquids from machines.

Various domestic and commercial appliances/machines contain water when in normal operation, for example clothes washing machines and dish-washers, and leakage of the water from such machines can cause considerable damage to the machine and/or its surroundings if not remedied at an early stage.

According to one aspect of the present invention there is provided an electrically controlled apparatus in combination with a liquid sensor element which is positioned externally of the apparatus, so as to receive liquid leaking therefrom, and is connected with circuitry for detecting the presence of such liquid on the sensor element and thereupon providing an alarm and/or safety response.

According to a second aspect of the present invention there is provided a liquid sensor element, suitable for use as the sensor element of the last preceding paragraph, comprising mutually spaced electrode members provided in contact with a porous material, for receiving liquid to be detected, such that the porous material permeated by the said liquid can provide an electrical connection between the said electrode members.

Reference will now be made, by way of example, to the accompanying drawings, in which: Fig. 1 shows a circuit diagram of part of a combination embodying the said one aspect of the present invention; Fig. 2 shows a diagrammatic plan view of a first liquid sensor element embodying the said second aspect of the present invention; Fig. 3 shows a side elevational view of the liquid sensor element of Fig. 2; Fig. 4 shows a diagrammatic plan view of a second liquid sensor element embodying the said second aspect of the present invention; and Fig. 5 shows a side elevational view of the liquid sensor element of Fig. 4.

In the circuitry of Figure 1, a resistor R3 is connected between a detector terminal DET2 and the base of an npn control transistor TR1, the collector of which is connected to the base of a pnp drive transistor TR2. A resistor R5 is connected between the base of the transistor TR1 and a negative DC supply line 1, to which are connected also the emitter of the transistor TR1 and the collector of the transistor TR2.

A resistor R1 is connected between the collector of the transistor TR1 and the cathode of a diode D3, the anode of which is connected to a positive DC supply line 2. An alarm buzzer B1 is connected from the cathode of the diode D3 to the emitter of the transistor TR2, and a diode D1 having its anode connected to the emitter of the transistor TR2 is connected in parallel with the buzzer B1.

A detector terminal DET1 is connected to the positive supply line 2, and the components R1, R3, R5, TR1, TR2, D1, D3 and B1, connected as described above, form an alarm circuit for which the terminals DET1 and DET2 serve as sensor input terminals as described below.

A resistor R4 is connected between a third detector terminal DET3 and the base of an npn transistor TR3, the collector of which is connected to the base of a pnp transistor TR4 and also, through a resistor R2, to the positive supply line 2. A resistor R6 is connected between the base of the transistor TR3 and the negative supply line 1, which is also connected to the emitter of the transistor TR3 and the collector of the transistor TR4.

The emitter of the transistor TR4 is connected in series through the control winding of the latch relay RL2 and the control winding of the relay RL1 to the positive supply line 2.

A capacitor C1 is connected in parallel with the control winding of latch relay RL2 having its negative connected to the emitter of the transistor TR4. A diode D2 having its anode connected to the positive of the capacitor C1 is shunted across the control winding of the relay RL1. The switch path of the relay RL2 is connected between the emitter of the transistor TR4 and the negative supply line 1. A light emitting diode LED1 having its cathode connected to the control winding of the relay RLl is connected through the resistor R7 to the positive supply line 2".

The DC supply lines 1 and 2 are connected to respective output points of a DC power supply circuit comprising a bridge rectifier BR connected across the secondary of a mains transformer 3, the primary of which is connected across the output terminals of a mains isolating switch SW1. The switch SW1 receives power from a mains supply IP when the circuit is in use. One of the output terminals of the switch SW1 is connected via a line 4 to the normally closed terminal of the relay RL1, and in the normal (non-activated) condition of this relay the line 4 is thereby connected through a fuse Fl to a 'live' power output line 5.A 'neutral' power output line 6 is connected directly to the other output terminal of the switch SW1. The power output lines 5 and 6 lead to a mains output OP for delivering operating power to an appliance/machine.

When the relay RL1 is activated, the connection between the lines 4 and 5 is thereby broken, the latch relay RL2 is simultaneously activated thereby closing the circuit to the light emitting diode LED 1.

Additionally, a light emitting diode LED2 is connected by its cathode to the negative sup ply line 2, its anode connected through the resistor R8 to the positive supply line 2 and two auxilliary power supply sockets V1 and V2 are connected to the power output lines 5 and 6.

The components R2, R4, R6, TR3, TR4, D2, C1, RL1, and RL2, make up a cut-out circuit operable in dependence upon a signal input applied between the terminals DET1 and DET3 as described below.

When the switch SW1 is turned on, power will be supplied to the bridge rectifier BR, and the light emitting diode LED2 will be lit. When no electrically-conductive connection is provided between the terminals DET1 and DET2, the transistor TOR 1 is biassed off by the resistor R5 so that the transistor TR2 will be biassed off by a high voltage applied through the resistor R 1. However, if a sensor input provides a conductive connection between the terminals DET1 and DET2, the high voltage thereby applied from the positive supply line 2 by way of the voltage-divider R3-R5 to the base of the transistor TR1 will turn the transistor TR2 on.This will produce a fall in voltage across the resistor R1 with the result that the transistor TR2 will be turned on and the alarm buzzer B1 will be activated.

The cut-out circuit operates in dependence upon a sensor input applied between the terminals DET1 and DET3. Whilst these terminals are open-circuited, the resistor R6 holds transistor TR3 off and the resistor R2 accordingly holds transistor TR4 off so that the relay RL1 is in its normal (non-activated) condition connecting the power supply line 4 to the power output line 5. If the sensor input provides a conductive connection between the terminals DET1 and DET3, the transistor TR3 will be turned on by the high voltage thereby applied through resistor R4, and in consequence the transistor TR4 will be turned on by virtue of a large potential drop produced across the resistor R2. Conduction through the transistor TR4 will activate the relay RL1 so that the power output line 5 is disconnected from the AC power supply line 4 and the flood warning Diode LED1 is lit.At the same time, the relay RL2 will be activated so as to close its nor mally open switching path between the collector of the transistor TR4 and the negative supply line 1. This will serve to maintain the activation of the relay RL1 thereafter, whatever may happen to the transistor TR4, until the AC power input is discontinued, for example by opening of the switch SW1.

Figures 2 and 3 show a liquid sensor element in the form a rectangular mat comprising two porous absorbent sheets 7 and 8, for example of highly permeable paper, having sandwiched between them an impermeable film 9, preferably of a plastics material, an upper side of which carries inter-digitated but mutually separated metallic-strip electrode members 10 and 11 (shown as seen on removal of the sheet 7) in contact with and covered by the upper absorbent sheet 7. The lower side of the impermeable film 9 carries a metallic strip-form electrode 12 extending peripherally around the film 9 in contact with the lower absorbent sheet 8. The sheet 7 is smaller than and positioned centrally on the film 9, which in turn is smaller than and positioned centrally on the sheet 8 as shown.

The electrode members 10, 11 and 12 are provided with respective electrical connection terminals 13, 14 and 15 and when the sensor element is to be used with the circuitry of Figure 1 the sensor terminals 13, 14 and 15 are connected respectively to the detector terminals DET1, DET2 and DET3 of Figure 1.

The power input of a machine to be protected against leakage is connected to the output OP of Figure 1, and the mat-like sensor element is placed beneath the machine so as to receive any leakage therefrom.

A small amount of water leaking from the machine onto the upper absorbent sheet 7 of the sensor element will be dispersed by the absorbent sheet so as to set up an electrically-conductive connection between the electrode members 10 and 11, and thus between the terminals DET1 and DET2 of Figure 1. As described above, this will actuate the alarm circuit so as to cause the alarm buzzer B1 to sound. Meanwhile, the presence of the impermeable film 9 prevents the absorbed water from providing a conductive connection between the electrode members 11 and 12.

A larger leakage of water from the apparatus will cause the upper absorbent sheet 7 to become saturated so that excess water will run over the edge of the impermeable film 9 and become absorbed into the lower porous sheet 8 so as to be brought into contact with the electrode member 12. In this way an electrically-conductive connection is provided between the sensor terminals 14 and 15, in addition to the conductive connection already existing between the sensor terminals 13 and 14, so that a conductive connection is thereby provided between the cut-out circuit input terminals DET1 and DET3. As a result, the relay RL1 will be activated so as to disconnect the live power output line 5 from the switch SW1, this condition being held subsequently by the latching relay RL2, as described above.

Thus the machine will be switched off, and the flood warning diode LED1 will be illuminated.

The auxilliary output sockets V1 and V2 can be used for the electrical control of respective water inlet valves for the machine, and will also be deprived of power when the cut-out circuit operates.

Figures 4 and 5 show a liquid sensor element which differs from the sensor element of Figures 2 and 3 primarily in the arrangement of the electrode members. The sensor element of Figures 4 and 5 comprises a porous, absorbent sheet 17, for example of highly permeable paper, and an impermeable film 19, preferably of a plastics material, an upper surface of which carries mutually separated metallic-strip electrode members 20 and 21 (shown as seen on removal of the sheet 17) in contact with and covered by the absorbent sheet 17. The lower side of the impermeable film 19 is covered completely by a metallic sheet-form electrode 22, of the same peripheral form and dimensions as the film 19.

The electrode members 20, 21 and 22 are provided with respective electrical connection terminals 23, 24 and 25, and when the sensor element is to be used with the circuitry on Figure 1 the sensor terminals 23, 24 and 25 are connected respectively to the detector terminals DET1, DET2 and DET3 of Figure 1.

The sensor element of Figures 4 and 5 operates in a similar manner to the sensor element of Figures 2 and 3. A small amount of water leaking from the machine onto the absorbent sheet 17 of the sensor element will be dispersed by the absorbent sheet so as to set up an electrically-conductive connection between the electrode members 20 and 21, and thus between the terminals DET1 and DET2 of Figure 1, thereby actuating the alarm circuit as described above. Meanwhile, the presence of the impermeable film 19 prevents the absorbed water from providing a conductive connection between the electrode members 21 and 22.

A larger leakage of water from the apparatus will cause the absorbent sheet 17 to become saturated so that excess water will run over the edge of the impermeable film 19 so as to be brought into contact with the sheetform electrode 22. Thus, an electrically-conductive connection is provided between the sensor terminals 23 and 25, in addition to the conductive connection already existing between the sensor terminals 23 and 24, so that a conductive connection is thereby provided between the cut-out circuit input terminals DET1 and DET3 of Figure 1 and the cutout circuit is actuated, as described above.

The arrangement of the electrode members 20, 21 and 22, as shown in Figure 4, is such that if the liquid sensor element is too wide to be easily placed beneath a machine which is to be protected, it may be cut in stages to a smaller size without causing the sensor element to become inoperative. The sensor element may be reduced in width by first cutting the sensor element along line 26-26, thereby incapacitating only a small portion 27 of the electrode member 21. Further reduction in width may be obtained by cutting the sensor element along line 28-28. If reduction in depth is required, the sensor element may be cut along line 29-29.Since the electrode member 22 is in the form of a sheet extending over the complete area of the impermeable sheet 19, cutting the sensor element as described above does not cause any problems with regard to the electrode member 22.

The electrode member 22 and impermeable sheet 19 are conveniently provided by a metal foil backed plastics sheet of a type similar to that used to back domestic radiators to reflect heat.

The circuitry of Figure 1 may be incorporated in a self-contained unit which can be plugged directly into a mains socket, the machine which is to be protected being then plugged directly into an output socket of the unit. Such a unit will preferably have separate sockets for the connection of the sensor element and any electrically controlled water inlet valves such as are mentioned above. Alternatively, the circuitry of Figure 1 could be built into the machine concerned during its manufacture, the circuitry being then preferably encapsulated in resin or other plastics material and fixed within the cabinet of the machine. In this case, the circuitry of Figure 1 can be wired directly into an electrical supply circuit of the machine, and the indicator diodes LED1 and LED2 mounted on the control console of the machine.

It is possible that a minor water leak, which should not incapacitate the machine, could fall onto the edge of the sensor element and provide a conductive connection between the cutout circuit input terminals DET1 and DET3, thereby switching off the machine. To avoid this possibility, a by-pass switch could be incorporated into the unit in order to by-pass the cut-out circuit but leave the alarm circuit active, thereby permitting the continued use of the machine, in the event of such a leak, whiist actuating the alarm to call attention to the water leak.

Claims (8)

1. An electrically controlled apparatus in combination with a liquid sensor element which is positioned externally of the apparatus, so as to receive liquid leaking therefrom, and is connected with circuitry for detecting the presence of such liquid dn the sensor element and thereupon providing an alarm and/or safety response.

2. A liquid sensor element, suitable for use as the sensor element of claim 1, comprising mutually spaced electrode members provided in contact with a porous material, for receiving a liquid to be detected, such that the porous material permeated by the said liquid can provide an electrical connection between the said electrode members.

3. A combination as claimed in claim 1, wherein the said liquid sensor element is an element as claimed in claim 2.

4. A combination as claimed in claim 3, wherein the sensor element has a further electrode member which is separated from the electrode members of claim 2 so that such liquid received from the said apparatus will tend to establish an electrical connection, between the said further electrode member and another electrode member of the element, only after such electrical connection has been provided between the electrode members of claim 2, and wherein the said circuitry has three input terminals connected respectively to the three electrode members and is arranged to respond to the provision of an electrical connection between the electrode members of claim 2 by activating an audible or visible alarm, the provision of an electrical connection between the said further electrode member and the said other electrode member of the element causing the circuitry to interrupt the supply of power to the apparatus.

5. A combination as claimed in claim 4, wherein the electrode members of claim 2 are sandwiched between an upper surface of an impermeable sheet and an upper sheet of such porous material, and the said further electrode, member is sandwiched between the lower surface of the impermeable sheet and a lower sheet of such porous material.

6. A combination as claimed in claim 4, wherein the electrode members of claim 2 are sandwiched between an upper surface of an impermeable sheet and an upper sheet of such porous material, and the said further electrode covers the lower surface of the impermeable sheet.

7. A combination as claimed in claim 1, substantially as hereinbefore described with reference to Figures 1 to 5 of the accompanying drawings.

8. A liquid sensor element as claimed in claim 2, substantially as hereinbefore described with reference to Figures 2 to 5 of the accompanying drawings.