JPH03171584A - Electric heater - Google Patents

Abstract

PURPOSE: To prevent damages due to overcurrent by connecting a plurality of heating elements in parallel, and arranging a relay contact connected to one of the heating elements in series and a relay operating coil connected to a power source through a temperature-sensing resistor. CONSTITUTION: Heating resistors R1, R2 having positive temperature coefficient are connected to a cooking hot plate in parallel, and a pair of normal open contacts S1 of a relay device is connected to the resistor R2 in series. The resistors R1, R2 are connected to a switching device S2 in series between power source terminals. An operating coil C of the relay device is connected to a temperature-sensing resistor T is series between the power source terminals. When power is switched on for operation, a contact S3 is closed, and the contact S1 is opened against the force of a spring P with the coil C. The resistor R1 by receives power and raises the temperature. When the temperature of the resistor T is raised, current of the coil C is decreased, and the hot plate reaches a safe raised temperature, the contact S1 is closed, power is supplied to the resistor R2, and current flowing through the resistor T becomes negligible.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an electric heater suitable for use in a kitchen.

BACKGROUND OF THE INVENTION Conventionally, electric heaters, such as hot plates, as described above, have typically been equipped with a wound wire resistor having an extremely low temperature coefficient of resistance. As a result, the electrical resistance and the corresponding output were almost independent of the temperature of the hot plate itself under any control conditions.

The inventors have found it advantageous to manufacture the hot plate resistor from a material that has a positive temperature coefficient of resistance. According to this resistor, the output is highest when the resistor is at a low temperature in any setting state, and the output decreases as the temperature of the resistor increases. This allows for a faster temperature rise and reduces the risk of the hotplate catching fire or scorching if it is inadvertently left at maximum power without any cooking utensils on it.

When such a hot plate is switched on in a cold state, the resistance of the resistor is in a low state and the initial current is at a maximum. Thereafter, as the temperature of the hot plate increases, the current value decreases.

In some cases, the initial current may be such a high value that it causes an unacceptable change in the mains voltage in a particular area, or the fuse does not trip or the overload protection device trips. The present invention is to provide an electric heater, such as an electric hot plate 1, that does not cause such problems.

SUMMARY OF THE INVENTION The object of the invention is an electric heater suitable for use in a kitchen, comprising a heating element (resistive element), two or more of the heating elements having at least one mode of operation. are connected in parallel with each other, said heating elements have a positive temperature coefficient with respect to electrical resistance, and said electric heating element further includes a contactor of a relay connected in series with one of said heating elements; and a relay actuation coil connected to a power source via an attached temperature-sensitive resistor, and the contact of the relay is configured to close when the temperature of the electric heater rises. It is achieved by an electric heater.

Accordingly, one or more, but not all, of the resistors of the electric heater are connected in parallel with each other and in series with the contacts of the switch or relay, so that they are not normally energized. The switch or relay closes only when the temperature of the heater increases.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

The figure shows two different types of circuits for an electric heater, such as a hot plate, according to the invention.

As shown in FIG. 1, the cooking hot plate includes two heating resistors (R1) and (R2). Both of these resistors are formed of materials that have a substantially positive temperature coefficient of resistance. The two resistors are connected in parallel with each other, and the resistor (R2) is connected in series with a pair of normally open contacts (S1) of the relay device. A pair of parallel resistors (R1) and (R2) are connected in series with a switching device (S2) between the power source terminals. The switching device (S2) serves as a power regulator.

The actuating coil (C) of the relay device is connected in series with a temperature sensitive resistor (T) between the power source terminals.

The temperature-sensitive resistor (T) also has a high positive temperature coefficient of resistance. A switch (S3) is attached to the control shaft of the power regulator (S2).
) is arranged to close when the power regulator is switched on before power is supplied to the resistors (R1) and (R2).

When the power is switched on during operation, the contact (S3)
is closed, the circuit for this actuating coil (C) is closed, and the contact (S1) is held open by the actuating coil (C) against the force of the spring (P). As a result, no power is initially supplied to the resistor (R2), while the resistor (R1) receives power and the temperature of the hot plate begins to rise. When the resistor (R1) receives power supply, the temperature of the temperature-sensitive resistor (T) increases, which causes the actuation coil (
The current flowing through C) decreases. When the hot plate reaches a safe elevated temperature, the force of the actuating coil (C) overcomes the force of the spring (P), and the contact (S1) closes.
City power is supplied to the second resistor (R2). Thereafter, the temperature of the hot plate rapidly rises to the operating temperature, at which the current flowing through the temperature sensitive resistor (T) becomes negligible, and the contact (S1) remains closed.

In another embodiment, similar to the example shown in FIG. 1, the switching device (S2) is not a power regulator but a series-parallel multi-position switch. Thereby, a plurality of resistors, usually three to four, can be connected in various states of series and parallel connections. For high output settings, two or more resistors are connected in parallel, and the relay contact (S1) is connected in series with at least one, but not all, of the resistors.

In this case, the switch (S3) is provided so as to close before the multi-position switch is set to a high output state and the resistors are connected in parallel.

FIG. 2 shows another embodiment of the invention. In this example, one of the heating resistors (R1) and (R2) acts as a temperature-sensitive resistor, and the actuating coil (C) of the relay device
control the current flowing through the

The relay device is of the quick-acting type and the contacts are normally closed. When a sufficiently large current flows through the actuation coil (C) and the coil is actuated, the contact (S1) is connected to the spring (P
) opens rapidly against the force of

In operation, when the switching current is first turned on, the current temporarily flows through both resistors (R1) and (R2).

However, the large current flowing through the resistor (R1) and the actuating coil (C) opens the contact (S1), so that the current flowing only through the resistor (R1) is reduced to [1]. The temperature of the hot plate rises, the current flowing through the resistor (R1) and the working coil (C) decreases, and the working coil (
When the force due to C) cannot overcome the force of the spring (P), the contact (S1) closes. Even in such a structure, the aforementioned multi-position control switch or power regulator can be used.

The invention is particularly suitable for hot plates of the type in which the enameled metal plate is provided with a film (e.g. a thick film) of resistive material formed over an enameled insulating layer to form the heating element. If the hot plate has the structure shown in Fig. 1, the hot plate is equipped with a temperature-sensitive resistor (T).
has. Such a hot plate construction is particularly advantageous.

This is because such hot plates have a small heat capacity.
Therefore, the temperature rises relatively quickly, and there are many suitable resistor materials that cannot be drawn into the wire form of conventional resistor types, but can be formed into thick films. be. Such resistor materials are described in European Patent Publication No. 0286215, 0
No. 286216, No. 0286217 and No. 0300685
It is stated in the No. The materials described in these publications have an electrical resistor track (tr) having the following structure.
ack). That is, the metal part and the glass part have suitable resistance values and coefficients of thermal expansion, and are compatible with the electrically insulating material in which the tracks are formed, so that the tracks can adhere to the electrically insulating material.

[Brief explanation of the drawing]

1 and 2 are schematic diagrams showing main parts of mutually different embodiments of the electric heater according to the present invention. (C)... Operating coil (P)... Spring (R1), (R2)... Resistor (S1), (S2), (S3)... Contact (and above) Fjgj. Fig. 2.

Claims (1)

[Scope of Claims] [1] An electric heater suitable for use in a kitchen, comprising a heating element (resistance element), two or more of the heating elements being configured to operate in at least one mode of operation. connected in parallel with each other, the heating elements have a positive temperature coefficient with respect to electrical resistance;
The electric heater further includes a relay contact connected in series with one of the heating elements, and a relay actuation coil connected to a power source via a temperature-sensitive resistor attached to the electric heater. . An electric heater, wherein the contact of the relay is configured to close when the temperature of the electric heater increases. [2] controlled by a power regulator or series-parallel switch and connected in series with a temperature sensitive resistor to ensure that the relay contact opens when power is first applied to the heating element; The electric heater according to claim 1, further comprising a switch. [3] The electric heater according to claim 1, wherein one of the heating elements constitutes a temperature-sensitive resistor that controls the current flowing through the relay actuation coil. [4] Claim [1] characterized in that the relay is controlled by a series-parallel switch and operates only in a high output setting state in which two or more heating elements are connected in parallel.
] to [3]. The electric heater according to any one of [3]. [5] The electric heating device according to any one of claims [1] to [4], comprising a metal plate covered with enamel, and the heating element is formed as a resistance film on the enamel surface. vessel.