GB2258772A

GB2258772A - Immersion detection circuit interruptor

Info

Publication number: GB2258772A
Application number: GB9117451A
Authority: GB
Inventors: Hin Ming Lam
Original assignee: Defond Manufacturing Ltd
Current assignee: Defond Manufacturing Ltd
Priority date: 1991-08-13
Filing date: 1991-08-13
Publication date: 1993-02-17
Also published as: GB9117451D0

Abstract

An immersion detection circuit interrupter, e.g. for a hair drier, has an immersion sensor 14 directly connected to a secondary relay 20 for operating a primary trip device 12. The secondary relay and primary trip device may be incorporated within an appliance plug body. <IMAGE>

Description

IMMERSION DETECTION CIRCUIT INTERRUPTER This invention relates to immersion detection circuit interrupters which can be used to isolate the power supply to an electrical appliance on detection of the product being immersed in water or other liquids.

Immersion detection circuit interrupters (IDCI's) are fairly well-known in which a signal from an immersion detector sensor is amplified or otherwise modified to provide a suitable output signal to operate a tripping device to isolate the power supply to the appliance. The circuit for modifying the sensor's signal is generally of a complex nature involving the use of electronic components and most preferably using integrated circuits. A typical prior circuit is depicted in Figure 1.

Use of such an electronic circuitry adds to the expense of the circuit interrupter as well as affecting the reliability by introducing more components which can fail.

Hence, the object of the present invention to provide an immersion detection circuit interrupter which is simple in construction and reliable in use.

Accordingly, the present invention provides an immersion detection circuit interrupter for isolating the power supply to an electrical appliance comprising: an immersion sensor which generates an electrical signal when a predetermined moisture level is detected; a trip device having contacts arranged to isolate the power supply and a trip solenoid for operating the trip device; and a secondary relay having a coil and a contact, wherein the coil is directly connected to the immersion sensor and arranged so that the relay is operable by the electrical signal from the immersion sensor and the contact is arranged to operate the trip solenoid to isolate the power supply on operation of the secondary relay.

Preferably, the trip device and the relay are located within the body of a plug for connecting the appliance to the power supply.

Preferred embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings in which: Figure 1 is a circuit diagram for a conventional IDCI; Figure 2 is a circuit diagram for an IDCI according to a preferred embodiment of the present invention; Figures 3 and 4 illustrate a typical immersion sensor arrangement which may be employed with the present invention as applied to a hair drier.

According to the conventional IDCI as shown in Figure 1, the IDCI has a trip device comprising contacts 10 actuable by a tripping mechanism 11 which is operated by a trip solenoid 12. The contacts 10 are located in the power supply for the electrical appliance for isolating the power supply when the trip device is actuated. Electronic circuitry, generally indicated by box 13, is used to amplify the signal received from the immersion sensor, not shown but generally connected at 14.

The electronic circuitry in this simple form, comprises an MOV for preventing power supply surges from damaging the electronic circuitry, a SCR which, when triggered, operates the solenoid 12 and a capacitor C1 connected across the output of the SCR. The trigger circuit for the SeR comprises resistors R1 and R2, diode D and capacitor C2 connected to the output of the sensor.

Turning now to Figure 2, you can see that the preferred embodiment of the present invention has a trip device comprising a tripping mechanism 11 actuable by a trip solenoid 12 and arranged to operate contacts 10 in the power supply for the appliance. However, in this embodiment a secondary relay 20 is provided which has a contact 21 which completes the electrical circuit for the tripping solenoid 12 across the power supply. Coil 22 for the secondary relay 20 is connected between the sensor and the power supply such that the electrical signal from the sensor is passed directly to the coil of the secondary relay operating the relay and closing the contact 21. This in turn actuates the trip device by operating the solenoid 12 which actuates the tripping mechanism 11 to open contacts 10, thus isolating the appliance from the power supply.

In this embodiment, the electronic devices have been eliminated from the operating circuitry of the IDCI.

A number of immersion sensors are available but the commonly used form comprises a phosphorous bronze wire which is located about the appliance in the areas where water, etc.

is likely to enter when the appliance is immersed. The construction of the sensor is not of particular importance to this invention.

Turning now to Figures 3 and 4 in which a hair drier 40 is depicted for reference only, to illustrate the arrangement of a preferred immersion sensor. As previously mentioned, the immersion sensor comprises a phosphorous bronze sense wire 15 which is laid around the various openings of the hair drier and around the heating element 41. When the appliance is immersed, leakage current from the supply connected to the motor, heating element and/or switch is picked up by the sense wire which represents a low resistance return path through the coil of the secondary relay. This current is sufficient to operate the secondary relay to initiate operation of the solenoid 12 of the tripping mechanism 11 to isolate the supply by opening contacts 10.

Phosphorous bronze is normally chosen as the sense wire for its physical strength and elastic properties. However, it should be realised that any particular form of sense wire may be used, and indeed any type of immersion sensor would most probably operate satisfactory with the present invention.

In the physical arrangement of the appliance, the IDCI would most likely be located within the plug of the appliance cord. The appliance cord would be a 3 core cord having 2 cores for the active and neutral lines (or Line Cores) and a 3rd core for the sensor signal. The sensor line would normally be a smaller core as it is not intended to carry substantial or sustained current.

For larger appliances, the IDCI may be located in the appliance itself but it is preferred for the contacts and hence the trip device to be located within the plug of the appliance cord to isolate the supply as close as possible to the source.

Claims

1. An immersion detector circuit interrupter, for isolating the supply to an electrical apparatus comprising; an immersion sensor which generates an electrical signal when a predetermined moisture level is detected; a trip device having contacts arranged to isolate the electrical supply and a trip solenoid for operating the trip device; and a secondary relay having a coil and a contact wherein the coil is directly connected to the immersion sensor and arranged so that the relay is operable by the electrical signal from the immersion sensor and the contact is arranged to operate the trip solenoid to isolate the power supply on operation of the secondary relay.

2. An immersion detector circuit interrupter as defined in claim 1 wherein the appliance is connectable to the electrical supply by means of an appliance cord and plug and wherein the immersion sensor is located in the appliance itself and the trip device and secondary relay are located within the plug of the appliance cord.

3. An immersion detector circuit interrupter substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.