JPS5928814B2 - Heating time control device - Google Patents

Description

Detailed Description of the Invention The present invention uses a humidity sensor to detect changes in humidity values caused by heating, and processes them to control the heating time of a heated object. The present invention relates to a means for cleaning contamination.

In general, the method of using a humidity sensor to detect changes in the humidity value of the heated object and controlling the heating state is one of the effective methods for automating the control of heating time in ovens such as microwave ovens. It is.

However, the humidity sensors used in this method generally have a characteristic that their electrical resistance changes depending on the presence or absence of adhesion of water vapor particles on the sensor surface, and therefore, if the sensor surface becomes contaminated, the sensor It has the disadvantage of reduced sensitivity.

Particularly when used in a microwave oven, it is inevitable that components such as oil and soybean oil will evaporate and adhere to the sensor, so it is necessary to remove these contaminants from the sensor surface.

One of the most effective means of removing contaminants is burning them off.

The present invention provides, for example, a timing for cleaning a humidity sensor as a means for detecting a heating state of a microwave oven by removing contaminants using a burning means;
It is characterized by its control circuit and mechanism.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a heating time control section of a microwave oven according to the present invention. In the figure, 1 is a food to be heated, and 2 is a humidity sensor, which detects changes in humidity generated from the food to be heated 1, and detects the humidity. The change is amplified by amplifier 3.

4 is a signal comparison processing circuit, which compares the level of changes in humidity with a preset reference value H, and
A control signal sh is outputted to the power control circuit 6 of.

It also has a control terminal that enables input of the detection signal h1 using the signal E.

The power control circuit 6 has a function of supplying power to the magnetron 5 using a heating start signal 7 and stopping the power supply using a control signal sh.

Although the above configuration is the principle of the heating time control method using the humidity detection means, the present invention further includes means for decontaminating or cleaning the humidity sensor, such as a stick.

That is, a cleaning operation timing control circuit 8 and an applied power control circuit 1 for the heater 9 near the humidity sensor.
Cleaning is performed by newly adding 0 and cooling means 11 for the humidity sensor.

Here, the positional relationship between the humidity sensor 2 and the heater 9 is
4 and 5, a heater 9 is wrapped around the sensor 2, and the surface of the sensor 9 is heated by heat dissipation from the heater caused by applying power to the heater. , a method is used to burn off contaminants attached to the surface.

FIG. 2 is a timing chart showing the cleaning sequence of the sensor nailed by the timing control circuit 8.

hl is a detection signal obtained by amplifying the humidity change detected by the sensor 2, and P is a voltage applied to the heater 9, which is applied for a time T1.

C is a timing signal to turn on the fan as the cooling means 11, and turns on the fan for the time T2.
do.

E is a timing signal that controls whether or not to input the detection signal RI into the comparison processing circuit 4.TI+T2='l:'
After o hours, enable the input of hl to the comparison processing circuit 4,
The result is h2.

Note that after cleaning, that is, after heating the sensor 2, the fan serving as the cooling means 11 rapidly cools the sensor 2 to the ambient steady temperature value, and as a result, the relative humidity value detected by the sensor 2 is immediately changed to the steady value. It has the role of bringing it back to normal.

hl in FIG. 2 indicates the humidity change during and after cleaning.

That is, time t. At the same time, heater 9 starts heating.
When a suitable value of power is supplied for a time T1, the heat dissipation caused by the heating of the heater 9 raises the temperature of the sensor 2 to a value that burns off the contaminants on the surface, and as a result, the sensor 2 is cleaned.

With the passage of time T1, the relative humidity rapidly decreases due to heating, as shown in the second section.

Immediately after T1 time has elapsed, the fan 11 is operated for T2 time, and as the sensor 2 is cooled and returned to room temperature, hl increases and recovers to the steady relative humidity.

After the time T1+T2-To, the control signal E is activated and the normal humidity change due to heating the food is input to the comparison processing circuit 4.

Such timing is controlled by a timing control circuit 8.

Here, TI+T2 = T□ is determined by the thermal time constants of the heater 9 and the sensor 2, the cooling capacity of the fan 11, etc., and is a sufficiently short time compared to the time required to heat the food.

FIG. 3 shows an example of the configuration of a microwave oven for effectively performing a cleaning operation.

In FIG. 3, 12 is a heating chamber that accommodates the food to be heated 1, and 13 is a punched metal plate that allows a moisture stream such as water vapor generated by heating the food 1 to pass therethrough and blocks microwaves. , 14 are arranged at appropriate angles and intervals with respect to the sensor 2 and the heater 9 so that the cooling air from the fan 11 as a cooling means for the sensor 2 and the heater 9 effectively hits the sensor 2 and the heater 9. An air passage connecting the air outlet 15 and the fan 11, 16 a power supply terminal to the heater 9, 17 a terminal for the sensor 2, 1
8 is the exhaust port of the microwave oven.

The opening also shows the flow of cooling air coming out of the air outlet 15 and after cooling the sensor 2 and heater 9.

Furthermore, C is the cooling air from the magnetron 5 that is introduced into the refrigerator and discharged from the exhaust port 18. The heat of the air whose temperature has increased by cooling the magnetron 5 is applied to the food to be heated, thereby increasing the overall thermal efficiency of the microwave oven. The purpose is to improve

The cooling air from the magnetron passing through the exhaust port 18 hits the contaminants to be burned away during cleaning of the sensor 2, and has an important effect of promoting the burning of the contaminants and performing effective cleaning. demonstrate.

4 shows one specific embodiment of the power control circuit 10 for the heater 9, which is particularly effective when the required heater power is small.

In FIG. 4, 19 is a transistor that drives a relay 20, and the base current of the transistor 19 is limited by a series resistor 21.

A signal P1 is applied to this terminal 22 to control the time for applying electric power to the heater 9.

20a is a contact of the relay 20, and when the relay 20 is energized, the contact is closed.

23 is a transformer, and the turns ratio is determined according to the rated value of the heater 9.

24 is a power supply, which is usually a commercial power supply (50Hz/60H2
).

The secondary side of the transformer 23 is directly connected to the heater 9 of the sensor 2.

The amplitude of signal P sufficiently turns transistor 19 on for time T1.
If the pulse value is enough to change to N, relay 20 is used only for T1.
is energized, the contact 20a closes, and a predetermined power is applied to the heater 9.

When the current capacity of the heater 9 is small, it can be easily turned on and off using relay contacts, which has the advantage of simplifying the circuit configuration.

FIG. 5 shows another embodiment of the power control circuit 10 for the heater 9, which is effective when the power required for the heater 9 is large.

Reference numeral 25 is an AC power source, which is a 50 Hz or 60 Hz commercial power source.

26 is a transformer having an appropriate turns ratio for operating the phase control circuit 44; 27 is a half-wave rectifier diode; 28
is a resistor for limiting the current of the constant voltage diode 29,
43 is PUT (Program-mable Uniju
It is a well-known fact that an intermittent oscillation circuit is constructed by interconnected resistors 30, 31, 32, and 33, and a capacitor C.

35 is a logical product (AND) circuit which outputs the logical product of the control signal P and the intermittent oscillation output C, and drives the transistor 38 with the output signal.

37 is a pulse transformer, 39 is a thyrisk, and 44 is a resistor for controlling the gate current of the thyrisk.

The thyristor 39 is coupled in series with the heater 9 and connected to the commercial power source 25.

FIG. 6 shows signal waveforms of each part of the control circuit shown in FIG. 5.

The operation of the circuit will be explained with reference to FIGS. 6 and 5.

In Figures 5 and 6, ■ac is AC power supply 2
This is the voltage waveform of No. 5.

Due to the diode 27 and the constant voltage diode 28, the voltage waveform at point a becomes as shown in (2)a.

The voltage waveform at point b becomes like ■b1, and therefore the waveform at point C becomes like VC.

That is, a pulse synchronized with the power supply voltage waveform Vac is supplied to point C.

The time τ in FIG. 6 can be adjusted by varying the resistor 30.

Here, when a signal PP is added as one input signal of the AND circuit 35, the pulse Vc force ζ is selected and outputted by the AND circuit for a time T1, and triggers the thyristor 39 through the transistor 38 and the pulse transformer 37.

As a result, the waveforms of the current flowing through the sirisk and the heater become as shown in 1, and the heater 9 is heated by the current i for a time T11.

Control of the current i is possible by changing the time τ, ie the firing angle of the thyrisk.

This circuit is effective when the rated current of the heater 9 has a large effective capacity because it can be controlled without using a large capacity relay contact.

As a thyristor, it can be easily inferred that a bidirectional thyristor can be used.

As stated above, according to the present invention, the humidity sensor can be cleaned in an extremely short time, so each time food is heated, it can be cleaned in a short time at the beginning of heating, and the sensitivity of the sensor can be regenerated and maintained. It is.

As a result, the heating state of food can be detected while keeping the humidity sensor at its highest sensitivity at all times, so the practical effect on an automatic heating control device using humidity detection is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a heating time control device using humidity detection according to the present invention, FIG. 2 is an explanatory diagram showing the cleaning sequence of the humidity sensor, FIG. 3 is a diagram showing the arrangement of the cleaning means, and FIG. 4 5 is a circuit diagram showing one embodiment of the heater power control circuit, FIG. 5 is a circuit diagram showing another embodiment of the heater power control circuit, and FIG. 6 is an explanatory diagram of the operation of the embodiment shown in FIG. 5. . 1... Food to be heated, 2... Humidity sensor, 4... Processing circuit, 9... Heater,
10... Heater power control circuit, 11...
- Cooling means.

Claims (1)

[Scope of Claims] 1. A humidity sensor that detects a change in humidity arising from a food to be heated, a processing circuit that compares the humidity change with a preset reference value and determines the heating time of the food, and the humidity sensor. and a heater power control circuit that applies appropriate power to a heater near the humidity sensor, and heats the humidity sensor for an appropriate period of time in the initial stage of heating. A heating time control device that maintains ventilation. 2. The heating time control device according to claim 1, wherein the heater power control circuit is configured to control power by changing the phase and application time of voltage applied to the heater. 3. The heating time control device according to claim 1, wherein the heater power control circuit is configured to control power by changing the amplitude and application time of voltage applied to the heater. 4. Heating time control according to claim 1, wherein the cooling means comprises an air outlet provided at an appropriate angle with respect to the humidity sensor and the heater, and an air passage connecting the air outlet and the air blowing means. Device. 5. The heating time control device according to claim 1, wherein the cooling means is configured to operate for an appropriate time after the heater is energized.