JPH02227623A - Pyroelectric sensor - Google Patents

Abstract

PURPOSE:To allow stable control over a long period of time by adhering a pyroelectric by a low-hardness adhesive agent onto a conductive plate body and molding the plate body, the pyroelectric, electrode and lead wires by a low-hardness resin. CONSTITUTION:The pyroelectric 2 having the compsn. consisting of a lead titanate system and a lead zirconate system is adhered by the low-hardness adhesive agent 3 of a silicon system onto the metallic plate 1. A pair of electrodes 4 are formed to this pyroelectric 2 and the lead wires 5 respectively coated with the resin are connected from the electrodes 4. Further, the metallic plate 1 on the side where the pyroelectric 2 is adhered, the pyroelectric 2, the adhesive agent 3, the electrodes 4, and the lead wires 5 are molded by the low-hardness resin 6 of the silicon system and the lead wires 5 are fixed and held on the resin 6. Stable control is executed over a long period of time without peeling the pyroelectric 2 and without generating cracks in the mold by using the adhesive agent 3 and the resin 6 having the low hardness in such a manner.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention 1-II Field of the Invention The present invention relates to a pyroelectric sensor that utilizes the pyroelectric effect of a pyroelectric substance, and relates to a sensor that is applied, for example, to automation of reheating in a microwave oven.

BACKGROUND OF THE INVENTION Conventionally, there is a humidity sensor as shown in Figure 7 as a sensor used to automate reheating in a microwave oven.
Sensor chip 19, heater 20, resin base 21. It is composed of a mesh cover 22 and a terminal 23. Since the resistance value of the sensor chip 19 changes due to changes in humidity (steam generated from the food), the controller detects the cooking state of the food using the voltage divided by the reference voltage and the resistance (not shown). Ta.

When the heater 20 is used in a microwave oven, the sensor chip 19 is used to refresh the sensor chip 19 from being contaminated by food gas, oil, etc., and the mesh cover 22 is used for wind protection and as a power saving section of the heater 20. It is used for (
National Technical Report Vo1.29No.
3) Also, a case will be described in which the pyroelectric sensor 7 as shown in FIG. 1 is used to automate reheating in a microwave oven.

The pyroelectric sensor 7 includes a metal plate 1, a pyroelectric body 2, an adhesive 3, an electrode 4, and a lead wire 5. In a pyroelectric sensor, hot water vapor from food is passed through a metal plate 1 to a pyroelectric body 2.
Only when a thermal change is applied to the pyroelectric body 2, a pyroelectric current flows through the pyroelectric body 2 and is observed as a voltage if a resistor is connected to the outside. In other words, the end of reheating the food is determined at the point in time when water vapor from the food is applied to the pyroelectric body 2 as a thermal change. Regarding the characteristics of the sensor, see 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 the above-mentioned humidity sensor, gas and oil in the food adhere to the humidity sensor during cooking, reducing the detection sensitivity. The heater for the refresh heat treatment must be used to remove the deposits on the humidity sensor, which generates extra power and costs.In addition, since the voltage across the resistor is used as a control signal, the humidity of each component Variations in sensor resistance and power supply voltage lead to variations in control signals, making management difficult.

Furthermore, when a pyroelectric sensor is used, although its configuration is an hour wheel compared to a humidity sensor, the following problems arose.

(1) Recently, with the spread of microwave ovens with toaster functions, the sudden heat shock of hot air from the heater causes cranks to occur in the pyroelectric material through adhesives, etc. due to the difference in thermal expansion coefficient between the metal plate and the pyroelectric material. However, the sensor function sometimes disappeared.

(2) At the same time, when similar heat shielding was applied to the resin that protects metal plates and pyroelectric bodies from moisture, cracks occurred in the resin, which resulted in insufficient moisture-proofing and deterioration of sensor function. .

Means for Solving the Problems In order to solve the above problems, the pyroelectric sensor of the present invention relates to adhesion between a conductive plate and a pyroelectric material, and uses a low-hardness adhesive to connect the conductive plate and a low-hardness resin. It is configured to be molded.

According to the present invention, the low hardness adhesive has the effect of counteracting the strain caused by the difference in thermal expansion between the pyroelectric body and the plate.

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

FIG. 1 is a cross-sectional view of the pyroelectric sensor 7. FIG. A pyroelectric material 2 having a lead titanate-based and lead zirconate-based composition is adhered onto a metal plate 1 with a low-hardness silicon-based adhesive 3. A pair of electrodes 4 are formed on the pyroelectric body 2, and resin-coated lead wires 5 are connected to each electrode 4, and a metal plate 11 on the side to which the pyroelectric body 2 is bonded, the pyroelectric body 2, The adhesive 3, electrodes 4, and lead wires 5 are molded with a low-hardness silicone resin 6, and the lead wires 5 are fixedly held on the resin 6.

FIG. 2 is a block diagram of the main body of a microwave oven having a pyroelectric sensor 7 of the present invention. A heating chamber 9 into which food 8 is placed and taken out;
Magnetron 10 for high frequency heating of food 8. Exhaust part 11
, a pyroelectric sensor 7 provided in the exhaust section 11, and a magnetron 10
A cooling fan 12 that cools the heating chamber, a duct 13 that blows some of the air from the cooling fan 12 to the heating chamber, a filter 14 that filters the output signal of the non-electric sensor 7, an amplifier 15 that amplifies the filter signal, and a control means 16. It is configured. In addition, 18 is a heater for a toaster (sometimes used for toasting bread).

Automation of reheating of food 8 is performed as follows. The food 8 is placed in the heating chamber 9, and the magnetron lO
A part of the cooling air is guided to the heating chamber 9 via the duct 13. A portion of the cooling air is shown by a solid arrow line 17, and water vapor generated from the food 8 is shown by a dotted arrow line. Part of cooling air 1
7 and the water vapor generated from the food 8 are exhausted to the outside through the exhaust section 11.

Here, Fig. 3 shows an example of the output voltage waveform regarding the signal and noise of the pyroelectric sensor 7 when 400 cc of water is heated. Fig. 3 shows the change over time until the water in the heating chamber 13 boils. The signal waveform shown in FIG. 4 is the result of spectrum analysis of this waveform.

As can be seen from FIG. 4, when warm water vapor hits the pyroelectric sensor 7, a large signal change is seen in the 0 to 20 Hz band. A is when the water in the heating chamber 13 has boiled, water is before boiling, C is when the microwave oven is not energized,
The difference between the a and the mouth is about 30 dB, and the signal level is a few? It is the voltage of Iv. Therefore, a waveform passing through the filter 14 and amplifier 15 that passes the 0 to 10 Hz band is observed as shown in FIG. The control means 16 controls on/off of the magnetron 10 and the like based on this signal.

Next, FIG. 5 shows the temperature stress of the pyroelectric body 2 in a microwave oven having a toaster function. When a toaster is used, the heater 18 is turned on and bread or the like can be toasted. However, when the heater 18 is used for a long time, the inside of the heating chamber 9 rises, and the cooling fan 12 is turned on to protect the magnetron 10 and cool the heating chamber 9. Then, the hot air filling the heating chamber 9 due to the air blown by the cooling fan 12 applies a sudden temperature change to the pyroelectric body through the metal plate 1.

Therefore, in one embodiment of the present invention, a low-hardness silicone-based adhesive was used as an adhesive that can sufficiently cope with this rapid temperature stress.

FIG. 6 shows heat stress life data of conventional epoxy adhesives with high hardness and silicone adhesives with low hardness. The test conditions are a heat shock test of -40°C to 120°C and a 5-minute cycle at 60% humidity. With the highly hard epoxy adhesive, separation of the metal plate 1 and the pyroelectric body 2, cracking of the pyroelectric body 2, and cracking of the epoxy resin 6 occurred. However, low hardness silicone adhesive 3, tree 71! ! 6, no such phenomenon occurred.

This is because if the plate 1 and the pyroelectric body 2 are fixed with a highly hard adhesive, it will not be able to follow sudden temperature changes, and the pyroelectric body On the other hand, low hardness adhesives and resins such as silicone-based adhesives act as cushion-like thermal shock absorbers even when subjected to such sudden temperature changes, and the epoxy adhesive It is thought that no such phenomenon occurred.

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

(1) Even if a sudden temperature stress occurs in a device equipped with a heater, it is buffered by a low-hardness adhesive, so the pyroelectric material does not peel off, and stable control over a long period of time is possible.

(2) Furthermore, since the device is molded with a resin that has low hardness even when sudden temperature stress is applied, cranking does not occur, preventing moisture from entering and deteriorating the device.

(3) Since an adhesive with low hardness is used, it is possible to prevent voltage generation (piezoelectricity) due to distortion of the pyroelectric material due to sudden temperature stress.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a pyroelectric sensor according to an embodiment of the present invention, and FIG.
The figure shows the configuration of the main unit installed in the same microwave oven, Figure 3 shows the output waveform of the pyroelectric sensor, Figure 4 shows the spectrum analysis of the output waveform of the parfroelectric, and Figure 5 shows the pyroelectric sensor's output waveform. FIG. 6 is a diagram showing the temperature rise of a pyroelectric sensor with respect to the temperature stress of the electric current, FIG. 6 is a diagram showing life data of the sensor's heat shield adhesive, and FIG. 7 is a configuration diagram of a conventional humidity sensor. 1...Metal plate, 2...Pyroelectric material, 3...
...Adhesive, 4...Electrode, 5...
Lead wire, 6...Resin. Name of agent Patent attorney Shigetaka Awano 1 person Figure 1 I 2 Figure 1-A4 / 6 15 /'iL Figure 4 [After weighting] Figure 4 t [Twist] Binding ■ Figure Hee! -Introduction 40 and ~l & Guhi Minpuiku A (f,
I! gαri diagram, gi ginma

Claims (2)

[Claims] (1) A pyroelectric body that generates current by a temperature-changing medium such as water vapor or gas, a pair of electrodes formed on the pyroelectric body, a lead wire led out from the electrodes, and a conductive wire that connects the pyroelectric body. The pyroelectric sensor is bonded onto a plastic plate with a low-hardness adhesive, and the plate, the pyroelectric body, the electrodes, and the lead wires are molded with resins of various hardnesses. (2) The pyroelectric sensor according to claim (1), wherein the adhesive and the resin are made of a silicon-based material.