JPH06100505B2 - Temperature sensor and temperature detector using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a temperature detector, and more particularly to a temperature detector suitable for detecting a certain constant temperature.

(Prior Art) An infrared sensor is widely used as a sensor using a pyroelectric body. When the surface of the pyroelectric body, which is the body of the infrared sensor, is irradiated with infrared light, the infrared light is absorbed and the surface temperature of the pyroelectric body itself rises. At this time, the magnitude of the spontaneous polarization of the pyroelectric body has a relationship of decreasing with an increase in temperature, and the magnitude of the spontaneous polarization instantaneously changes due to the temperature change. Therefore, the charges on the surface of the pyroelectric body are in an unbalanced state, and the unbalanced portion of this surface is taken out from the high impedance circuit as a change in voltage to detect a change in temperature.

(Problems to be Solved by the Invention) An infrared sensor using a pyroelectric body uses an unbalanced state of charges on the surface of the pyroelectric body. It is necessary to install a chopper in front of the sensor so that infrared rays continuously emitted from the object are incident as intermittent light.

Further, when the chopper is used in this way, the infrared rays incident on the sensor are composed of an infrared ray emitted from an object and an infrared ray from the chopper. Since the output of the sensor is a signal corresponding to the temperature difference between the chopper and the object, in order to know the temperature of the object, the temperature of the chopper needs to be measured and added to the temperature difference obtained from the sensor output. For this reason,
It is necessary to install a metal resistor and an IC temperature sensor near the chopper.

Therefore, it is an object of the present invention to provide a temperature sensor using a very inflection point of a pyroelectric coefficient of a pyroelectric body and a temperature detector using the same, without using a chopper like an infrared sensor. is there.

(Means for Solving Problems) As a means for solving the above problems, the present invention provides a rhombohedral zirconate titanate having an extremely inflection point of pyroelectric coefficient within a range of −50 ° C. to + 130 ° C. A pyroelectric body made of a lead-based porcelain composition, and a surface facing the pyroelectric body or electrodes formed facing the same surface, respectively, by electric charges generated by a sharp temperature change of the pyroelectric coefficient, A temperature sensor for detecting a temperature is provided.

Further, the present invention has an extremely inflection point of the pyroelectric coefficient of −50 ° C. to +13.
A temperature sensor made of a rhombohedral lead zirconate titanate porcelain composition in the range of 0 ° C., each having electrodes on opposite surfaces, and a current-voltage conversion means for converting a pyroelectric current of the temperature sensor into a voltage. And a reference voltage setting means for setting a reference voltage corresponding to the extremely extreme temperature of the pyroelectric coefficient of the temperature sensor, and an output voltage of the current-voltage converting means and a reference voltage from the reference voltage setting means. And a comparator for discriminating the temperature of the object to be measured.

(Operation) That is, as a result of various studies focusing on the pyroelectric effect of the pyroelectric material, the present invention shows that in the rhombohedral lead titanate zirconate titanate-based ferroelectric ceramic composition, the rhombohedral shape is increased with increasing temperature. Low-temperature stable phase (FR (LT)) and high-temperature stable phase (FR) of crystalline ferroelectric phase
(HT)), but this phase transition temperature is uniquely determined by the composition, and the spontaneous polarization (Ps) changes rapidly between the low-temperature side phase transition point and the high-temperature side phase transition point. Then, along with this, the pyroelectric coefficient (λ = ΔPs), which is the temperature derivative of the spontaneous polarization
/ ΔT) found that it forms a very sharp inflection point,
The temperature is detected by using the peak value of the pyroelectric coefficient associated with this phase transition.

The pyroelectric body has a very inflection point of the pyroelectric coefficient of -50 ° C to +130
Any intrinsic or modified lead zirconate titanate porcelain composition within the temperature range of ° C can be used.
For example, according to JP-B 59-13803 and JP 52-64700 discloses such a two-component system of PbTiO ₃ -PbZrO _3, PbTiO ₃ -PbZr
A three-component system, a four-component system in which one or more oxides having a perovskite type, a complex perovskite type, a pyrochlore type, a bismuth layered type, or a tungsten-bronze type crystal structure is added to O ₃ , and further the above Two-component system, three-component system, four-component system to which an additive (for example, manganese, nickel, cobalt, silicon, lithium, iron, tungsten, indium oxide) is added, and further each of the above-mentioned component systems Examples include those in which a part of Pb is replaced with Be, Ca, Sr, and those in which Ti or Zr in each component system is partly replaced with Sn, Hf and the like. Each of these has a phase transition [(FR (LT)-(FR (H
T)].

The reason why the lead zirconate titanate-based porcelain composition is limited to the rhombohedral ferroelectric porcelain composition whose pyroelectric coefficient is within the temperature range of -50 ℃ to +130 ℃ is extremely curved. Point is -50
Below ℃, the temperature difference between the low-temperature side phase transition point and the high-temperature side phase transition point
Since the pyroelectric current peak becomes extremely flat as it reaches 80 ° C to 100 ° C, the inflection point cannot be detected very accurately, and if it exceeds + 130 ° C, the high temperature side phase transition point can approach the Curie temperature of the pyroelectric body itself. Therefore, the polarization of the pyroelectric material may be depolarized or depolarized.

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

FIG. 1 shows an embodiment of the temperature sensor according to the present invention.
Is a pyroelectric body, 2 is an electrode formed on both surfaces of the pyroelectric body, 3 is a lead wire connected to each electrode, and 4 is a coating film surrounding the pyroelectric body 1 and the electrode 2, which is made of a highly heat-conductive insulating material. The pyroelectric material 1 is formed of a rhombohedral lead zirconate titanate-based ferroelectric ceramic composition having a very great inflection point of pyroelectric coefficient within a temperature range of -50 ° C to + 130 ° C. . Also, although not shown,
The electrodes 2 and 3 may be formed so as to face one surface of the pyroelectric body 1.

The temperature sensor 5 produces a pyroelectric current as its temperature rises. The pyroelectric current (i) is i = λ × A × (, where A is the effective electrode area of the temperature sensor 5 and dT / dt is the temperature gradient. dT / d
t). The relationship between this temperature and pyroelectric current is
As shown in the figure, when the temperature reaches the inflection point on the low temperature side, the pyroelectric current begins to increase sharply, but when it reaches a certain temperature, it reaches the extremely inflection point and then sharply decreases. Then, when the temperature reaches the inflection point on the high temperature side, the pyroelectric current decreases to the same extent as at the inflection point on the low temperature side, and thereafter gradually starts to increase. Therefore,
A constant temperature can be detected by detecting the peak value of the pyroelectric current.

Further, since the pyroelectric current (i) and the effective electrode area (A) of the pyroelectric body are in a proportional relationship, the output signal can be increased by increasing A.

FIG. 2 shows an embodiment of a temperature detector using the temperature sensor, which basically comprises a temperature sensor 5, a current / voltage converter 6, a comparator 7, and a reference voltage setting means 8. However, an amplifier 10 is inserted between the current-voltage converter 6 and the comparator 7, and the output of the comparator 7 drives a drive circuit such as a relay. The reference voltage setting means 8 sets a voltage corresponding to the voltage Vmax output from the amplifier 10 at the peak of the pyroelectric current of the temperature sensor 5 as a reference voltage.

When the temperature detector 5 is used, when the temperature of the temperature sensor 5 rises, the pyroelectric current is converted into a voltage by the current-voltage converter 6, the output voltage is amplified by the amplifier 10, and then the comparator 7 is inverted. It is input to the input terminal. This comparator 7
The reference voltage Vo set by the reference voltage setting means 8 is input, and when the output voltage of the amplifier 10 reaches the reference voltage Vo, it is output to operate the drive circuit 9, and an alarm is issued by an alarm device such as a piezoelectric buzzer. Emit.

The output voltage V from the current-voltage converter 6 depends on both the pyroelectric coefficient and the temperature gradient, but since the dynamic range of the pyroelectric coefficient is high, the fluctuation of the temperature gradient of 2 to 3 times is the reference voltage. It can be removed by setting Vo appropriately.
Extremely inflection point temperature of pyroelectric coefficient can be detected with high accuracy.

(Example 1) Raw material, PbO (or _{Pb 3 O 4), SnO 2} , Sb 2 O 3, TiO 2
By using the general formula: yPBTiO ₃ -zPbZrO ₃ ………… (1) and xPb (Sn _1/2 Sb _1/2 ) O ₃ -yPBTiO ₃ -zPbZrO ₃ …………
The rhombohedral crystal porcelain composition represented by (2) was weighed so that each raw material mixture was wet mixed for 20 hours, dried, and then calcined at 750 ° C to 850 ° C for 2 hours. The calcined powder was wet-milled with an appropriate amount of organic binder for about 10 hours, dried, and sized with a 80-mesh sieve. 750-1000kg / cm of this powder
A square plate having a side of 50 ° C. mm and a thickness of about 12 mm was formed at a pressure of ² and baked at a temperature of 1150 ° C. to 1250 ° C., and each porcelain plate was polished to obtain a porcelain plate having a thickness of 150 μm.

After applying silver paste on both sides of each porcelain plate, bake it to form a silver electrode, dip it in insulating oil at 20 ° C-80 ° C, and
Polarization was performed by applying a DC voltage of 3.0 KV / mm. Then, solder the lead wires to the silver electrodes on both sides and 10 x 10 mm.
A temperature sensor having the structure shown in FIG.

Curie points and phase transition points of rhombohedral lead titanate zirconate-based ferroelectric ceramic compositions were measured using each temperature sensor as a sample. The results are shown in FIG. In the figure, △,
▲ is a plot of changes in the high-temperature side and low-temperature side phase transition points of the two-component composition, and ○ and ● are plots of changes in the high-temperature side and low-temperature side phase transition points of the three-component system composition. .

From this figure, when the composition of the binary or ternary lead zirconate titanate porcelain composition is determined on the rhombohedral side,
It can be seen that the phase transition point, and hence the inflection point on the low temperature side and the inflection point on the high temperature side of the spontaneous polarization amount, are each set at one point.

In addition, 0.05Pb (Sn _1/2 Sb _1/2 ) among the temperature sensors
O ₃ -0.07PbTiO ₃ -0.88PbZrO ₃ (Sample 1), 0.10Pb (Sn
_1/2 Sb _1/2 ) O ₃ -0.04PbTiO ₃ -0.86PbZrO ₃ (Sample 2) and 0.10Pb (Sn _1/2 Sb _1/2 ) O ₃ -0.08PbTiO ₃ -0.82PbZrO
₃ (Sample 3), which consisted of pyroelectric porcelain having each composition, were selected, and the temperature characteristics of their pyroelectric coefficients were measured. The results are shown in FIGS.

From these figures, all of Samples 1 to 3 are between the low temperature side inflection point and the high temperature side inflection point, specifically, 62 ° C. and 0 ° C., respectively.
It can be seen that the peak of the pyroelectric coefficient is shown at 60 ° C. and 61 ° C., and the peak value is about 4 to 8 times that at the stable phase.

Further, when the temperature sensor having the composition of Sample No. 1 was measured for changes in the temperature of the object to be measured and the pyroelectric current, the results shown in FIG. 3 were obtained. The temperature gradient of the measured object during measurement is 3
At ° C / min, the effective electrode area of the temperature sensor is 1 cm ² .

As is clear from FIG. 3, when the temperature of the object to be measured reaches 62 ° C., it is understood that the peak value of the pyroelectric current is exhibited.

(Example 2) PbO (or Pb ₃ O _4), using MgO, the _{Nb 2 O 5, TiO 2,} ZrO 2 as starting materials and in the same manner as in Example 1, 0.10Pb (Mg _1/3 N
A temperature sensor made of a pyroelectric material having a composition of b _2/3 ) O ₃ -0.05PbTiO ₃ -0.85PbZrO ₃ was fabricated and the temperature characteristics of its pyroelectric coefficient were measured. The results are shown in FIG.

From this figure, the temperature sensor of sample 4 also shows a peak of the pyroelectric coefficient between the inflection point on the low temperature side and the inflection point on the high temperature side, specifically, at 50 ° C., and the peak value is about the value in the stable phase. It can be seen that the value is four times.

(Example 3) 0.05Pb in the same manner as in Example _{1 (Sn 1/2 Sb 1/2) O} 3 -0.07
To obtain a pyroelectric ceramic having a composition of PbTiO ₃ -0.88PbZrO _3.
The porcelain was crushed to a particle size of 20 to 70 μm. This porcelain powder and NBR rubber, which is an organic substance, were mixed in a weight ratio of 94: 6. This mixture is heated at 170 ° C and pressure of 926 kg / cm ² for 30
After hot pressing for a minute, a composite pyroelectric material composed of a ceramic-organic material was obtained. The size of the sample is 10 mm on a side and 0.5 mm in thickness.
It was a square plate. Silver electrodes were vapor-deposited on both surfaces of this composite pyroelectric body, and lead wires were soldered to manufacture a temperature sensor having an effective electrode area of 10 × 10 mm and having the structure shown in FIG.

The temperature characteristic of the pyroelectric coefficient of this temperature sensor was measured, and the result is shown in FIG. From this figure, it can be seen that a peak of the pyroelectric coefficient is exhibited at 62 ° C. as in the case of only ceramics.

According to the temperature sensor including the composite pyroelectric body, the area can be easily increased and the output current can be easily increased. In addition, it is highly flexible, has a degree of freedom in selecting the shape, and can be easily attached to the object to be measured.

(Effects of the Invention) As is clear from the above description, the present invention is applicable to the phase transition between the low temperature side stable phase and the high temperature side stable phase possessed by the rhombohedral lead titanate zirconate titanate-based ferroelectric ceramic pyroelectric material. Since the temperature is detected using the peak value of the pyroelectric coefficient peculiar to the pyroelectric body, the detected temperature can be determined only by the composition of the pyroelectric body. Also, if the temperature is below the Curie point of the composition, the temperature characteristic curve of the pyroelectric coefficient is almost reversible and there is almost no hysteresis, and the peak value is determined only by the composition of the pyroelectric body, so fluctuations in the power supply voltage, etc. Even if there is an external cause, the constant temperature can be detected accurately regardless of it. Further, since the pyroelectric current of the temperature sensor, and hence the output voltage of the current-voltage converter, is proportional to the effective electrode area of the temperature sensor, excellent effects such as the production of the temperature sensor having an arbitrary output voltage can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a temperature sensor according to the present invention,
2 is a block diagram of a temperature detector using the temperature sensor of FIG. 1, FIG. 3 is a graph showing pyroelectric temperature characteristics of the temperature sensor according to the present invention, and FIG. 4 is a lead zirconate titanate porcelain. Graphs showing the relationship between the composition and the phase transition points and Curie points of the compositions, and FIGS. 5 to 9 are graphs showing the pyroelectric coefficient temperature characteristics of various temperature sensors according to the present invention. 1 ... Pyroelectric body, 2 ... Electrode, 3 ... Lead wire, 4 ... Thermally conductive insulating material, 5 ... Temperature sensor, 6 ... Current-voltage converter, 7 ... Comparator, 8 ... ... reference voltage setting means, 9 ...
… Drive circuit, 10… Amplifier.

Claims (2)

[Claims] 1. The extremely inflection point of the pyroelectric coefficient is -50 ° C to + 130 ° C.
Of a rhombohedral lead zirconate titanate porcelain composition within the range of, and an electrode formed respectively on the surface facing the pyroelectric material or facing the same surface, A temperature sensor that detects temperature by the electric charge generated by a sharp temperature change in the electric coefficient. 2. The extremely inflection point of the pyroelectric coefficient is -50 ° C to + 130 ° C.
Consisting of rhombohedral lead titanate zirconate titanate porcelain composition in the range of, and a temperature sensor having electrodes on the opposite surfaces, current-voltage conversion means for converting the pyroelectric current of the temperature sensor into a voltage, The reference voltage setting means for setting a reference voltage corresponding to the extremely inflection point temperature of the pyroelectric coefficient of the temperature sensor is compared with the output voltage of the current-voltage converting means and the reference voltage from the reference voltage setting means. A temperature detector comprising a comparator for discriminating the temperature of an object to be measured.