KR940003234B1 - Sensor circuit of microwave oven - Google Patents

Abstract

Cooking takes more time in a microwave oven which employs an absolute humidity sensor since the sensor requires heating stand-by time. The circuit is provided to reduce this stand-by time. On the initial power-up time, it feeds the 1st current value (90-120 mA) to a bridge circuit (10) thru a switch (30). After some pre-defined time, turn-off the switch (30) and normal current value (30-40 mA) to the bridge circuit (10) via a resistor (R1). Thus, the self heating time of the sensor can be reduced to one-third by supplying high current - three times as high as normal current level - to the bridge circuit at the initial time.

Description

Microwave Sensor Circuit

1 is a schematic diagram of a typical microwave oven.

2 is an exemplary circuit diagram of a sensor circuit of a conventional indirect detection type microwave oven.

3 is an exemplary circuit diagram of a sensor circuit of an indirect detection type microwave oven according to the present invention.

4 is another embodiment of the sensor circuit of the microwave oven of the indirect detection method according to the present invention.

* Explanation of symbols for main parts of the drawings

1: microwave oven body 2: sensor

3: sensor circuit 4,50 control part

5: cooking chamber 6: display device

7: Command key part 8: Power key

10: bridge circuit 20: amplification circuit

30: switch 40: time setting means

60: pulse generating means RC, RC: absolute humidity sensor

R1, R6: resistor C1, C2: capacitor

Q1: transistor D1: diode

U1: Operational Amplifier

The present invention relates to a microwave oven, and more particularly to a sensor circuit of the microwave oven for improving the initial start time.

In recent years, microwave ovens have been automated, diversified and diversified according to the remarkable development of semiconductor devices. The microwave oven includes a memory device storing a cooking program, a temperature or humidity sensor, a microcomputer, a command key unit, and the like. Therefore, the microcomputer reads the command generated through the command key unit and detects the cooking state of the food through a temperature or humidity sensor according to the indicated cooking program, and controls the magnetron, the heater, and the motor to perform the indicated cooking.

Microwave ovens or sensor ovens used in the United States and Europe, where meat is mainly used, are used as a temperature sensor in the form of a metal rod type probe that is directly plugged into food.

However, in a variety of oriental foods, that is, Korea and Japan, a temperature rod in the form of a metal rod is inadequate due to its eating pattern. Therefore, the absolute humidity sensor is used to detect the cooking state of food indirectly. Absolute humidity sensor is for detecting the absolute humidity in the cooking chamber of the stove generates an electrical signal according to the amount of water vapor generated by heating the food.

Therefore, an indirect detection sensor oven with a cooking program for detecting the cooking state of food when using an absolute humidity sensor has been developed.

This indirect detection sensor oven range has led to the expansion of the automatic cooking menu, simplified operation, and improved taste.

Known absolute humidity sensors consist of two thermistors. One thermistor (Rc) is sealed by sealing the dry air (absolute humidity of about 0.0g / m3) and the other thermistor (Rc) has a good thermal conductivity with the sealing chamber in which the one thermistor (Rc) is installed It is installed in the combined open room to form the humidity part.

The sealing chamber and the open chamber are combined with each other with good thermal conductivity to achieve a heat balance with respect to the environmental temperature of both devices. The absolute humidity sensor is normally operated after initial heating to a constant current, for example, a current of about 30 to 40 mA at a self heating temperature, for example, a temperature of about 150 ° C to 180 ° C.

Therefore, in the conventional sensor-orange using the absolute humidity sensor, since the absolute humidity sensor is normally operated after self-heating after the cooking is selected, it takes much time to cook and has a great influence on the optimum cooking according to the food.

It is an object of the present invention to provide a sensor circuit of a microwave oven capable of shortening the self heating time of the absolute humidity sensor in order to solve the problems of the prior art as described above.

Another object of the present invention is to provide a sensor circuit of a microwave oven which can reduce the cooking time of the microwave oven.

In order to achieve the above object, the present invention provides a sensor circuit of an indirect detection type microwave oven configured as a bridge circuit by using an absolute humidity sensor. It is characterized in that it is provided with a current supply means for supplying a current to the first current value to reach, and then to supply a current to the normal second current value.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic diagram of a general microwave oven, in which reference numeral 1 is a microwave oven main body, 2 is a sensor, 3 is a sensor circuit, and 4 is a control unit (or a microcomputer). In the microwave oven body 1, a cooking chamber 5, a display device 6, a command key portion 7, a power key 8, and the like are shown, and a magnetron, a heater, various motors, and the like are provided. The sensor 2 is installed at a predetermined position in the cooking chamber 5. The control unit 4 is composed of a microcomputer and reads the absolute humidity in the cooking chamber 5 sensed by the sensor 2 through the sensor arc passage 3 and receives a command through the command key unit 7 and the power key 8. do.

The cooking process is performed by controlling the magnetron, the heater, and various motors according to the stored cooking program according to the received command.

Referring to FIG. 2, the sensor circuit of the conventional indirect detection type microwave oven constitutes a bridge circuit 10 using absolute humidity sensors Rs and Rc and resistors R2 and R3 and outputs the bridge circuit 10. Amplified by the amplification circuit 20 for amplifying and supplied to the control unit 4.

The bridge circuit 10 is coupled to the supply power supply (Vcc) through the current limiting resistor (R1).

Therefore, the current supplied to the bridge circuit 10 is determined according to the value of the current limiting resistor R1. Known absolute humidity sensors Rs and Rc have a self-heating temperature of about 150 ° C. at a supply current of about 39-40 mA, which takes about 120 seconds after energizing.

And the output characteristic has the voltage characteristic of 5㎷ ± 1.0 에서 at 40 ℃, 35g / m3. The amplifying circuit 20 is composed of an operational amplifier U1, resistors R4, R5, and a capacitor C1 to amplify the number mv of the bridge circuit 10 by several v. The amplifier circuit 20 has an amplification factor of several hundred times depending on the ratio of the resistors R4 and R5. The controller 4 reads the absolute humidity information through the amplifying circuit 20 in the on state of the power key 8.

In the conventional sensor circuit 3, since the value of the current supplied to the absolute humidity sensors Rs and Rc is kept constant, it is necessary to take time to heat up to the self heating temperature. Since it can be read, it takes longer to cook.

Referring to FIG. 3, in the present invention, when the initial power is turned on, a first current value, for example, about 90 to 120 mA is directly supplied to the bridge circuit 10 through the switch 30, and after a predetermined time, the switch ( 30) is turned off and a current of 30 to 40 mA, which is a normal holding current, is supplied to the bridge circuit 10 through the resistor R1. The switch 30 is turned on / off by the time setting means 40. In FIG. 3, the same reference numerals are used as in the circuit of FIG. 2 except for the initial current supply means including the switch 30, the time setting means 40 and the pulse generating means 60. In FIG. In the embodiment of the present invention, the switch 30 is composed of a PNP type transistor Q1. The output terminal Q2 of the pulse generating means 60, which generates a constant pulse signal when the DC power supply Vcc is applied, is connected to the trigger terminal T of the time setting means 40, and the magnetic term R6 and the capacitor C2 are connected. The delayed signal outputted to the output terminal O1 by the time constant of is connected to supply to the base of the PNP type transistor Q1.

Therefore, the PNP transistor Q1 applies a trigger signal to the time setting means 40 when the pulse signal generated from the pulse generating means 60 at the initial power-on, so that the time setting means 40 is applied to the constant time transistor Q1. The transistor Q1 is turned on by outputting a low signal to the base, and after a predetermined time, the transistor Q1 is turned off again. That is, the supply time of the first current value, that is, the current of 90 to 120 mA can be set by the time constant of the resistor R6 and the capacitor C2.

4 is a circuit diagram of another embodiment of the sensor circuit of the microwave oven according to the present invention, which comprises the time setting means 40 of FIG. The control unit 50 turns on the PNP transistor Q1 of the switch 30 by generating a control signal in a "low" state for a predetermined time through the output port OP when the power key 8 is turned on.

When the predetermined time, that is, the time when the absolute humidity controllers Rs and Re have reached the self heating temperature, a control signal in a "high" state is generated at the output port OP to turn off the switch 30 and the resistance R1. Make sure that the normal holding current is supplied through

As described above, in the present invention, when the initial power is turned on, the current of about 90 to 120 mA, which is about three times higher than the lifetime maintenance current through the switch, is supplied to the bridge circuit to shorten the time to reach the self-heating temperature of the absolute humidity sensor by three times. Can be.

Therefore, it is possible to shorten the cooking time by bringing the response characteristics of the sensor in the microwave quickly and to improve the taste of the cooking because the optimum cooking time can be adjusted accordingly.

Claims (3)

In the microwave sensor circuit of the indirect detection method using an absolute humidity sensor, the absolute humidity sensor reaches a self heating temperature in electricity by setting the current value supplied to the absolute humidity sensor as a large current value at the beginning of cooking. The sensor circuit according to claim 1, further comprising an initial current supply means for supplying a normal holding current. 2. The sensor circuit according to claim 1, wherein the large current value supplied at the beginning of the cooking process is about three times the normal holding current. The method of claim 1, wherein the initial current supply means is connected to the parallel connection tube switch to the means for supplying the normal maintenance current, and turn on the switch during the time the absolute humidity sensor reaches the heating temperature from the beginning of the cooking start And a time setting means and a pulse generating means for keeping it in a turn-off state thereafter.