EP0062082A1

EP0062082A1 - Heat-sensitive safety resistor

Info

Publication number: EP0062082A1
Application number: EP81102544A
Authority: EP
Inventors: Pai I. Kuo
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-04-03
Filing date: 1981-04-03
Publication date: 1982-10-13

Abstract

The present invention relates to a thermally-sensitive safety resistor comprising a heat-sensitive switch (7) formed by an insulating piece (1) provided with two bimetallic strips (3), a ceramic bushing (4) into which the heat-sensitive switch is inserted, and a resistance coil (5) wrapping around the bushing. The on-and-off of the switch (7) can be actuated by the heat produced by the resistance coil (5) when a current passes therethrough, thereby affecting on the switch to make or break the circuit.

Description

The present invention is concerned with a heat sensitive safety resistor which is formed by providing each of the two sides of a silicon insulating piece with a heat-sensitive bimetallic strip which can only contact with each other by the silver contact at the free end thereof, and inserting the resulting assembly into a ceramic bushing which contains composition of good heat conductor such as aluminum, magnesium or zirconium and which is externally provided with two inserters interconnected with each other through a resistance coil wrapping around the bushing. The ceramic bushing and resistance coil are externally enamelled, or overlaid with non-combustible material. In so doing, when the current in the circuit reaches a predetermined value, the heat thereby produced would render the connection or the disconnection of the bimetallic strips. Thus it can be used to determine the value of current, or to indicate if the circuit is overloaded.
Conventional ammeters suffer several disadvantages. They are relatively complicated in structure, thus rendering the liability of trouble, making its maintenance difficult, and entailing high cost of production. Moreover, the parts thereof tend to be damaged by undue use in operation-, such as erroneous wiring and so forth. Also, its relatively large size results in its inconvenience in use. For these reasons, they are not adapted to domestic use, in determining a specific value of electricity for a certain circuit. Thus the user cannot be alarmed when the circuit is electrically overloaded.
Accordingly it is the object of this invention to provide a heat-sensitive safety resistor having simple layout and small size to be adapted to domestic use.
It's another object of this invention to provide a safety resistor which can give out an alarming signal when the circuit is overloaded.
These objects of this invention will be accompanied by embodiments as referred to in relation with the annexed drawing of this invention as following.

Fig. 1. is a fragmentary view of this invention;
Fig. 2 is a side view of the insulating piece with bimetallic strips;
Fig. 3 is a wiring diagram of an embodiment according to this invention;
Fig. 4 is & circuit diagram of a parallel circuit of a multi-sectional alarming device according to this invention;
Fig. 5 is a circuit diagram of a series circuit of a multi-sectional alarming device according to this invention;
Fig. 6 is a graphical representation of the multiple- contact heat-sensitive switch according to this invention.

With reference now to the drawing, particularly Fig. 2 thereof, this invention comprises a silicon insulating piece (1) on which there are mounted two bimetallic strip (3) respectively positioned on the two opposite flat sides thereof, which two bimetallic strips can only contact with each other by a silver contact (2) disposed thereon, which constructs the heat-sensitive switch (7), thereby controlling the making-up or breaking of the circuit through the adjustment of adjusting screw (3¹) and the thermal expansion of the bimetallic strip to-result in the on or off of the switch when the temperature rises to a critical degree.
The circuit can be electrically connected to an alarming signal device, say a bulb, the lightness of which may vary with the power consumption so that the bulb gives out a stronger light when the power consumption is high.
Referring to Fig. 1, this-invention is formed by inserting the heat-sensitive switch (7) described hereinbefore into a ceramic bushing (4) containing composition of good heat conductors such as aluminum, magnesium, or zirconium. Also, each of the two ends of resistance coil (5) is respectively connected to an inserter (6). The ceramic bushing is externally glazed with a layer of enamel or non-combustible material. When an excess electricity passes through resistance coil (5), the resulting heat can be transferred through the ceramic bushing to affect on the heat-sensitive switch, to open or close the circuit. Referring now to Fig. 3, there is'shown a wiring diagram of the general switch of a domestic power supply system. When switch (8) is switched on, if the full load of the circuit is approached so that the melting of the fuse is impending, the heat produced by the resistance coil (5) is just enough to switch on the heat-sensitive switch in series connection therewith to sound buzzer (9). Meanwhile bulb (10) gives out an alarming signal to remind the user of the safety of using electricity. The measurement of the approximate current passing through a certain circuit can be carried out by varying the resistance coil or heat-sensitive switches (7). Besides, this invention can also be applied to electrical mosquito smudge or electric hair curler to avoid the risk of overheating by way of short circuit.
A plurality of resistors according to this invention can be connected in series or in parallel, to achieve multiple- sectional alarming effect. As shown in Fig. 4, a 0.2 ohm resistor which actuates the switch at 100^oC, a 0.3 ohm resistor which actuates the switch at 75°C, and a 0.5 ohm resistor, at 50°C, are connected in parallel, to the resistance coil. The heat-sensitive switches are respectively connected to loop circuits having bulbs of different color. With the increasing of the electric current, different bulbs of different hues are stepwise lit, thereby achieving the effect of multiple sectional alarming. Alternatively, the example suggested in Fig. 5, in which the resistors are connected in series, can accomplish similar effect as well.
Further, the heat-sensitive switch can be designed as shown in Fig. 6, wherein the diverse silver contacts are spaced apart by gaps of different width, to render the different electrical path to be built up at different temperature, so as to achieve multiple sectional alarming effect.

Claims

A heat-sensitive safety resistor, comprising a ceramic bushing (4);
an insulating piece (1), provided with two bimetallic strips (3) to form a heat-sensitive switch to be inserted into said bushing; said two bimetallic strips being mounted on said insulating piece in a manner so that they can be brought into electrical connection or electrical disconnection with each other thermally; a resistance coil (5)wrapping around said bushing; said ceramic bushing, heat-sensitive switch (7), and resistance coil being disposed so that the heat generated by the electric current passing through said resistance coil can affect on said heat-sensitive switch (7), and thus make or break the circuit of said heat-sensitive switch when the electrical load of said resistor reaches a predetermined value.