JPH01250052A - Piezoelectric element applied sensor - 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 Field of the Invention The present invention relates to a piezoelectric element, and particularly to a humidity sensor related to a microwave oven.

2. Description of the Related Art A conventional humidity sensor of this type is comprised of a sensor chip 25, a heater 26, a resin paste 27, a mesh cover 28, and a terminal 29, as shown in FIG. Since the resistance value of the sensor chip 25 changes depending on humidity, the controller detects the cooking state of the microwave oven using a voltage divided by the reference voltage and the resistance. Heater 26
The mesh cover 28 is for refreshing the sensor chip because it gets dirty with food gas, oil, etc. when used in a microwave oven, and the mesh cover 28 is for windproofing and is used to protect the heater
It is used to save power.

(National Technical Report Vo1.29 Nα3
TAN1983) Also, a case will be described in which an ultrasonic microphone is used as a temperature sensor as shown in FIG.

The microphone includes a piezoelectric element 1, a spacer 30, a terminal 31, a vibrating section 32, a case 33, a lead wire 34, an inner ring 35, a terminal plate 36, and silicone rubber 37. Regarding the detection of the cooking state of food, Japanese Patent Application Laid-Open No. 62-11292
This is shown in Publication No. 9.

Problems to be Solved by the Invention However, when using a humidity sensor as described above, gas and oil in the food adhere to the humidity sensor during cooking, reducing the detection sensitivity, so it must be refreshed every - time. The deposits on the humidity sensor must be evaporated using a heater for heat treatment, which generates extra power and cost.In addition, the voltage across the resistor is used as a control signal, so when producing a large number of The resistance of the humidity sensor, which is a component,
Variations in resistance and power supply voltage lead to variations in control voltage signals (this made management difficult).

Furthermore, when using an ultrasonic microphone, the shape of the case requires consideration of resonance frequency, vibration, etc., and due to the complicated temperature characteristics of the main piezoelectric element, if food is repeatedly heated in a microwave oven, the piezoelectric element 1 As the temperature of the attached exhaust part increases, the atmospheric temperature conditions of the exhaust part and the polarization current of the piezoelectric element detected also decrease, causing the problem that the heating end time is not constant when the same amount of food is heated. Ta.

In addition, piezoelectric elements are close to insulators, so leakage current increases when the environmental humidity is high, and the piezoelectric elements themselves are easily affected by humidity.

Means for Solving the Problems In order to solve the above problems, the humidity sensor of the present invention includes a piezoelectric element bonded on a metal plate, a correction element that compensates for a decrease in the output voltage of the piezoelectric element, and a humidity sensor that compensates for the influence of humidity. In order to prevent this, the piezoelectric element, correction element, and metal plate are integrally sealed with a non-moisture permeable molding material.

According to the present invention, both the piezoelectric element and the correction element have the same temperature as the ambient temperature, prevent the intrusion of humidity that adversely affects the characteristics of the piezoelectric element, and have the function of detecting the cooking condition of food with a simple configuration.

EXAMPLE Hereinafter, an example of the present invention will be described based on the accompanying drawings.

FIG. 1 is a sectional view of a humidity sensor 11 according to an embodiment of the present invention. A pair of vapor-deposited first electrodes 2 are applied to a lead titanate-based piezoelectric element 1, and are adhered to a metal plate 4 in electrical contact with an adhesive 3.

5 is a first lead wire led out from the metal plate (connected to ground), 6 is a temperature correction element, 7 is a second lead wire leading out the electrode at the other end of the piezoelectric element 1, and 8 is a lead wire leading out from the other end of the piezoelectric element 1; One end of the electrode of the temperature correction element is in electrical contact with the metal plate, and the other end is led out by a third lead wire 9. Note that the second and third lead wires are electrically insulated. 1o, the piezoelectric element 1, metal plate 4, correction element 6, and lead-out portions of the first, second, and third lead wires are molded with resin to prevent moisture permeability and are integrally sealed. has been done.

These constitute the piezoelectric element humidity sensor 11.

FIG. 2 is a block diagram of the main body of a microwave oven having the piezoelectric element 1 of the present invention. a heating chamber 13 into which food 12 is taken out and put in;
A magnetron 14 that heats the food 12 with high frequency, a piezoelectric humidity sensor 11 provided in the heating chamber exhaust section 15, a cooling fan 16 that cools the magnetron 14, a duct 17 that blows part of the air from the cooling fan 16 into the heating chamber, and a piezoelectric element. It is comprised of a filter 1B (hereinafter referred to as a filter) that filters the output signal of the humidity sensor 11, an amplifier 19 that amplifies the signal from the filter 18, and a controller 2o.

Detection of boiling of the food 12 is performed as follows.

The food 12 is arranged in the heating chamber 13, and the magnetron 14
A part of the cooling air is guided into the heating chamber 13 via the duct 17 by the cooling fan 16 . A part of the cooling air is transferred to the actual arrow line 21, and gas such as moisture generated from the food 12 is transferred to the ignition line 22.
It is shown in

The cooling air and the gas containing moisture generated from the food 12 are discharged to the outside of the heating chamber 13 through the exhaust section 15. Here, FIG. 3 shows an example of the output voltage waveform regarding the signal and noise of the piezoelectric element humidity sensor 11 when water is heated at 400°C. A shows an example of a signal waveform when the water in the heating chamber 13 boils. Panel b shows the results of spectrum analysis of this waveform. Piezoelectric element humidity sensor 11
0~ by being exposed to warm air containing warm water vapor
It can be seen that a large signal is emitted in the 50H2 band.

A is when the water in the heating chamber 13 has boiled, B is before boiling, C is when the microwave oven is not energized, and the difference between A and B is about 30 dB, and the signal level is: Several mV
voltage. Further, even when dirt was attached to the piezoelectric element sensor 1, the output waveform shown in FIG. 3 did not change. This is because the piezoelectric humidity sensor 11 generates a signal in response to thermal changes. Therefore, as shown in FIG. 4, a band-pass filter is created using a bypass filter 23 and a low-pass filter 24 to form a filter 18 having a passband from 0 to 5QH2 band for the output signal of the piezoelectric humidity sensor 1. ing. The controller 20 detects the signal obtained by amplifying the signal of the filter 18 with the amplifier 19,
Controls on/off of the magnetron 14.

FIG. 5 is a characteristic diagram of the ambient temperature (exhaust section 15) and the output signal of the piezoelectric humidity sensor 11. From this figure, it can be seen that the output voltage decreases as the ambient temperature increases. Therefore, by correcting the decrease in the output signal using a correction element 6 formed on a metal plate, the same amount of food can be cooked in the same amount of time even if it is heated repeatedly.

Note that the piezoelectric element 1, the correction element 6, and the metal plate are bonded with an adhesive and electrically short-circuited, which has the effect of simplifying the configuration and improving thermal responsiveness.

Further, by using a material having substantially the same coefficient of thermal expansion as that of the metal plate and the piezoelectric element, there is an effect of preventing the generation of an error voltage caused by unnecessary distortion due to a difference in coefficient of thermal expansion.

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

(1) A piezoelectric element constructed on a metal plate, a temperature correction element that compensates for the temperature characteristics of the piezoelectric element, and these are molded with resin to prevent the detection current of the piezoelectric element from leaking due to moisture. The configuration enables detection of stable heating conditions of food.

(21) Since the heating state of the food is detected by the response of the thermal change of the piezoelectric element, the design is very flexible and easy in terms of the shape of the metal plate, the arrangement of the piezoelectric element, and the correction element. There is no need for a heater to remove dirt, making it possible to make it lighter, thinner, and more compact.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a piezoelectric element applied sensor according to an embodiment of the present invention, Fig. 2 is a configuration diagram of the main body, Fig. 3 is an output waveform diagram of the same piezoelectric element humidity sensor, and Fig. 4 is the configuration of the same filter. 5 is a temperature characteristic diagram of the same ambient temperature and a piezoelectric element humidity sensor, FIG. 6 is a block diagram of a conventional humidity sensor, and FIG. 7 is a block diagram of a conventional ultrasonic microphone. 1... Piezoelectric element, 2.8... Electrode, 3
...Adhesive, 4...Metal plate, 5.7.
9... Lead wire, 6... Temperature correction element, 10... Resin. 1-m-Piezoelectric element 2.8 - Electrode 4-Gold A IO-Glue Figure 1/ Figure 2 1q Figure 3 Figure 4 Figure 5 C-Figure 6 Figure 7

Claims (4)

[Claims] (1) a piezoelectric element and a temperature correction element each having a pair of electrodes on a metal plate or a conductive plate body, and one end of each of the electrodes being electrically connected; and the metal plate or plate body; and a configuration in which lead wires led out from the other ends of the piezoelectric element and the temperature correction element, the metal plate or plate body, the piezoelectric element, the temperature correction element, and the lead-out portion of the lead wire are integrally molded with resin. A piezoelectric element applied sensor. (2) The piezoelectric element applied sensor according to claim 1, wherein the piezoelectric element and the temperature correction element are bonded to a metal plate or a plate body with an adhesive. (3) The piezoelectric element applied sensor according to claim 1, wherein the metal plate or plate body and the piezoelectric element are made of a material having substantially the same coefficient of thermal expansion. (4) The piezoelectric element applied sensor according to claim 1, wherein the resin is non-moisture permeable and integrally molded.