JPS60189895A - High frequency heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] "Unexpected industrial application field" is a high frequency heating device 7 with a gas sensor; i'
The present invention relates to a detection circuit for a gas sensor that improves changes in sensor sensitivity due to the driving environment.

Conventional f! l ljM and its Problems In order to automatically terminate microwave heating, high-frequency heating apparatuses equipped with gas sensors that detect water vapor and various gases generated from objects to be heated are widely put into practical use. Examples of such gas sensors include the relative humidity sensor "Humiceram" manufactured by Matsushita Corporation, the absolute humidity sensor "Neo Humiceram" manufactured by Matsushita Corporation, and the gas sensor manufactured by Figaro Corporation.

FIG. 2 shows a typical example of a detection circuit for such a conventional gas sensor. Gas sensor Rs Reference resistance Ro in K0 column
is connected, which divides the input voltage Vin and inputs the output voltage Vout to the A/D converter. The characteristics of this detection circuit are shown in Figure 3, where Vout=(Ro/
Rs 1 Ro) - Expressed in Vin. When Rs=Ro, the slope is the largest, that is, the sensitivity is high, so
The reference resistance RO is often selected according to the sensor resistance at normal temperature and normal humidity, for example, 20° C. and 60% (relative humidity).

Now, the humidity-resistance characteristic of the gas sensor is a straight line on a logarithmic graph as shown in FIG. That is, the sensor resistance R
The relationship between s and absolute humidity H is Rs=H'' ((Z: constant)
It is expressed as However, if we redirect kneading to the real axis → 11''i, we can see that the amount of change in resistance differs depending on the environment, as shown in Figure 5.

Now, low humidity HL, mark 1 (H8, high humidity HH each 1
Heating starts at the border, and △H water (gu,
ke occurs i1. It can be seen that the change amount ΔRL of the sensing resistance at low AMH is the largest, and the deviation becomes smaller as the temperature increases. Change in high humidity HH 1rX
It is only less than half of △RHtri and △R.

- force, looking back at the detection characteristics in Figure 3, fj, 1
l14 ml (fj7. degree H8 sensor work (anti-R3
= The sensitivity of Ro is good, but it decreases by 1 degree (d) in both high humidity (R-large) and low humidity (R8 Kokushi).The resistance change at low humidity (H) is large, so It is rather preferable to have such characteristics. However, high humidity (Hh)
The rib resistance y-111△R is smaller than △RS, and the third
In the detection special circle shown in the figure, sensitivity is clearly insufficient, and detection is delayed and overheating occurs.

In this way, the detection circuit for i, r is known from the environmental performance song, and q, '1! ';il f! The problem of one tooth degree missing at the boundary between ll' and jpu'j was overlooked.

The present invention is intended to solve the above-mentioned conventional problems, and aims to provide a detection circuit for a gas sensor with sensitivity independent of the environment.

In order to achieve the above goal, the high-frequency heating device i' of the present invention has a gas sensor connected in series with a standard 7 times smaller than this. The resistor and the operational amplifier (1
10) It has a configuration that detects the current that presses the gas sensor, and can improve the change in sensor sensitivity caused by the current.

Example of Fuj1 Hiki 4 Below, we will explain the example of Kibori 4 based on the drawings.
do.

FIG. 1 is a perspective view of a high frequency heating equipment according to the present invention.

A door body 2 is pivotally supported at f) fj +in of the main body 1 so as to be openable and closable, and an operation panel 3 is provided. This operation panel 3" has an automatic heating function of 1° using a gas sensor.
J auto key 4 is arranged.

FIG. 6 shows the detection circuit b1'5 which is an embodiment of Honkankiri 1.

An input resistor R4 is connected in series with the gas sensor R8, and the input resistor R4 is sufficiently smaller than the sensor resistor R8. For example, Matsushita's absolute humidity sensor "Neo Humiceram"
Standard 7.11 Sensor 1j- at humidity (20°C 260%)
(The resistance is about 900 Ω, but as a manual resistance, select several Ω to several tens of Ω. In this way, R((R8/'1
0), a voltage approximately proportional to the current flowing through the sensor appears across R1. This is amplified by the operational amplifier 5 which is an amplification circuit, and the output V'o u t jr A
/ Input to D converter.

The amplification degree of the operational amplifier is (R3/R2) times, and it can be driven with both power supplies of 1B and -B.

FIG. 7 shows such detection characteristics. Here, from the sensor physical properties diagram in Figure 5, low humidity H, standard Hs, high z! Heating is started in each environment of 1 HH, and water A is removed by △H from the object to be heated.
Picking up the points where % occurred, RL, R3, RH in Figure 7
The points change from C5ΔRL, ΔR8, and ΔRH, respectively, so that F at this time is almost the same.

By amplifying the sensor voltage ', I7 pressure which is proportional to lAt in this way, it is possible to detect IJ4. Since the l1 resistance does not decrease and, on the contrary, the sensitivity increases, it is possible to avoid a decrease in the resistance change 111 of the sensor at high temperatures. Therefore, overheating due to detection failure at high temperatures can be prevented.

FIG. 8 shows the construction of the heating device. Operation panel 3
The command input from the auto key 4 above is the control)■-
It is decoded by 6. Then, the control unit 6 supplies power to the magneton, which is the high frequency generating means 8, via the driver 7.
Start IJ. Inside the heating chamber 9, the object to be heated 10 is placed i19
It is placed on a plate 11. The mounting tray 11 is rotated by the motor 12! ,! li1. It is possible to improve the problem of drying and uneven heating.

As the heating progresses, steam and gas begin to be generated from the heated object 10. This water vapor is removed by fan 1, which is a means of ventilation.
3, the air is discharged from the exhaust guide 14 to the outside of the aircraft. A gas sensor 15 is disposed on this exhaust guide 14, and a sixth
After the detection circuit h1゛116 shown in the figure, the A/
Connected to D converter. The control unit can be realized using a microcomputer with a built-in 6-digit A/D converter.

Effects of 11l111 As described above, according to the present invention, the following effects can be obtained.

(1) A sensor detection circuit with detection sensitivity independent of the environment can be realized.

(2) Since the input resistance is small, it is possible to suppress impedance to a low level when combined with a gas sensor, which improves noise resistance.

[Brief explanation of drawings]

Fig. 1 is a perspective view of the main body of a heating device showing an example of misfire 1, Fig. 2 is a detection circuit diagram of a conventional gas sensor, Fig. 3 is a detection characteristic diagram of the same, and Fig. 4 is a humidity sensor of a gas sensor. -] Mr. grain,
11 Sex (double logarithm) diagram, Figure 5 Q time! ! i1 degree - resistance characteristic 1 (1 (real axis) diagram, Figure 6 is a detection circuit diagram of a gas sensor showing an embodiment of the present invention, Figure 7 is a detection characteristic diagram of the same, Figure 8
The figure is a diagram showing the same measures. 5 ・Jl'l ll'irf timesj, :;,;,6...
1jiJ 11th part, 8 ・', +, ', j, 'frequency generating means, 9 heating chamber, 10... object to be heated, 15 gas sensor, R4... input resistance. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 3 8 Figure

Claims (1)

[Claims] A heating chamber in which the object to be heated is placed, a high frequency generating means coupled to this heating chamber, and an electric power supply to this high frequency generating means.
, J bJi! 1lrlJ controller, a gas sensor that detects water vapor or gas generated from the object to be heated, a human resistance connected in series with this gas sensor and sufficiently smaller than this, and a voltage divided by this input resistance. A high-frequency heating device consisting of an amplifier circuit that amplifies the