【発明の詳細な説明】 ［産業上の利用範囲］ 本発明は人体の移動，有熱物体の有無など微少な熱線に
よる熱線強度の変化を検出する新規な方法に関するもの
である． ［従来の技術及び問題点］ 従来，サーミスタを使用して熱線強度の変化を検出する
方法として，マンガン，コバルト，鉄，銅，遷移金属の
複合酸化物よりなるNTC（Negative Temperature Coeffi
cient）サーミスタを使用する方法が実用化されてい
る．この方法は,NTCサーミスタの有する，熱線強度の増
加に対する導電率の増加を利用し,NTCサーミスタに流れ
る電流変化を測定することにより，熱線強度の変化を検
出するものである． しかしながら,NTCサーミスタは室温で使用できるという
長所を有する反面，抵抗温度係数（α）が一般に−４％
／℃程度と低く，測定感度が小さいという問題点を有し
ていた． 一方,NTCサーミスタと逆の特性を有するサーミスタとし
て,PTC（Positive Temperature Coefficient）サーミス
タが知られている．このPTCサーミスタは，チタン酸バ
リウムを基体とする組成が一般的であり，これらのPTC
サーミスタはPTCの特性を示す温度領域（以下,PTC領域
という）内で15ー100％／℃という極めて大きな抵抗温
度係数を示すものである． 従って，上記PTCサーミスタを使用することにより高感
度に熱線の変化を検出することが可能となる． しかしながら,PTCサーミスタのPTC領域は，一般に使用
環境温度よりも高い温度領域にあるため,PTCサーミスタ
の温度をかかる温度領域に調節する必要があった．従
来,PTCサーミスタを使用して熱線の強度変化を測定する
方法はいくつか報告されている。例えば、J.E.Ralph,ln
frared Phys.,22,245（1982）．には,PTCサーミスタを
外部ヒーターにより一定温度に加熱しながら，該PTCサ
ーミスタに測定用の微小の電圧を印加し、電流値の変化
を測定する方法が記載されている．ところが，上記測定
方法はPTCサーミスタの温度を一定に加熱することが困
難である．特に該PTCサーミスタの温度は，装置の使用
開始時，環境温度の変化等により長時間ハンチングす
る．そのため、熱線が作用していないときの電流値（初
期値）が安定せず，熱線の検出に誤差が生じやすいとい
う問題を有していた． また，上記加熱における問題点を解決する手段として，
使用環境温度にPTC領域を有するPTCサーミスタを使用す
る方法が考えられるが，かかる特性を有するPTCサーミ
スタは一般に抵抗温度係数が小さくなり，しかも使用環
境温度の変化によって抵抗値が数桁も変化し，増幅器を
使用する場合のマッチングが難しいという問題を生じ
る． 以上のような問題により,PTCサーミスタを使用して熱線
を検出する技術は未だ実用化されるに至っていないのが
現状である． ［問題点を解決するための手段］ 本発明者らは，抵抗温度係数の大きなPTCサーミスタを
熱線の検出に使用すべく鋭意研究を重ねた．その結果,P
TCサーミスタの定温発熱性を利用すれば，該PTCサーミ
スタのPTC領域内に安定して温度の制御ができること及
びPTCサーミスタにかかる自己発熱させるような電圧を
印加した状態においても,PTCサーミスタは良好な応答速
度及び感度を発揮し，特に上記PTCサーミスタを自己発
熱させる電圧を特定の範囲とすることにより，該感度を
より一層上昇させることができることを見いだし本発明
を完成するに至った． 本発明は,PTCサーミスタを使用して熱線を検出するに際
し，該PTCサーミスタの抵抗温度係数が負から正に変わ
る温度以上で且つ使用環境温度よりも２℃以上高い温度
領域に自己発熱する電圧を印加しながら，該PTCサーミ
スタに流れる電流変化を検出することを特徴とする熱線
の検出方法である． 本発明において,PTCサーミスタは公知の材質が特に制限
なく使用される．代表的なPTCサーミスタを例示すれ
ば，チタン酸バリウム（BaTiO3）を主成分としこれに異
種原子価の元素を微量添加して半導体化したチタン酸バ
リウム系PTCサーミスタ，ウレタン樹脂中にカーボンを
分散させたカーボン・ウレタン樹脂系PTCサーミスタ,Ti
O,TiO2,VO2，V2O3などの金属酸化物をメタクリル酸系ポ
リマー等のポリマー中に分散させた金属酸化物・ポリマ
ー系PTCサーミスタなどが挙げられる．この中で大きな
正の抵抗温度特性を示し，特性の安定なチタン酸バリウ
ム系PTCサーミスタが特に好適に用いられる． 上記のチタン酸バリウム系PTCサーミスタは，異種原子
価の元素を微量添加することによって原子価制御型半導
体としたセラミックスである．例えば,Baサイトを置換
する元素としてLa,Ceのような希土類元素が,Tiサイトを
置換する元素としてSb,BiやNbなどの元素が知られてい
る．これらの元素を0.05から0.4モル％添加することがP
TCサーミスタを半導体化させるために好適に用いられ
る． また，チタン酸バリウムを基本とした組成のPTCサーミ
スタのPTC領域は，該PTCサーミスタのPTC領域をシフタ
ーと呼ばれる添加物で変化させることで，−150℃から4
00℃まで連続的に変化させることができる．例えば，人
体検出のような微弱な熱線を検出するためには，素子の
感度を向上させるためにPTC領域を室温付近に下げるこ
とが好ましい．また，高温での熱線測定では素子の温度
を一定に保つためには,PTC領域が使用環境温度より高く
設定すればよい.PTC領域をシフトさせるために添加する
元素は特に限定されない．例えば,PTC領域を高温にシフ
トさせるためのシフターとしてはPbが,PTC領域を低温に
シフトさせるためのシフターとしてはSr,Sn,Zrが好適に
用いられる． さらに，チタン酸バリウム系PTCサーミスタの特性を向
上させるためには様々な添加物を添加することができ
る．例えば，抵抗温度特性を向上させるためにはMn,Cr,
Feなどの元素を0.01〜0.125mol％添加することが好適で
ある．本発明に用いるPTCサーミスタとしては抵抗温度
係数が高いほど、感度、素子温度の安定性が向上するた
め、使用素子温度で10％／℃以上の抵抗温度係数を有す
ることが好ましい。また，焼結体粒子の粒径を均一化
し，抵抗を低く抑え，耐電圧特性を向上させるために,C
aを３〜5mol％,Srを１〜30mol％,Pbを１〜50mol％Baに
置換することが好ましい．また，焼結時の焼結性を向上
させるためにSiO2，TiO2，Al2O3のような液相焼結を起
こさせる助剤を,0.5〜5mol％添加することが好ましい． 本発明において,PTCサーミスタの大きさは適宜決定すれ
ば良いが，電圧の印加による自己発熱を均一に行わせる
ために，厚み１〜200μｍの薄膜状とすることが好まし
い． 第１図は，本発明に使用するPTCサーミスタの代表的な
構造を示すものである.1はPTCサーミスタ,1−ａは電極,
1−ｂはリード線である． 本発明において,PTCサーミスタに印加する電圧はPTCサ
ーミスタをPTC領域で且つ使用環境温度より２℃以上高
い温度に自己発熱させるために必要な電圧であれば特に
制限されない．一般には,PTCサーミスタがPTC特性を示
し始める温度，すなわち,PTCサーミスタの抵抗温度係数
が負から正に変わる温度（以下Tfという）以上でPTCサ
ーミスタが最大の抵抗を示す温度（以下Tmという）以下
の範囲にPTCサーミスタを自己発熱させ，且つ使用環境
温度よりも２℃以上高い温度範囲にPTCサーミスタを自
己発熱させる電圧が適宜選択される。特に,Tf以上,Tf＋
（Tm−Tf）/2以下で且つ使用環境温度よりも２℃以上高
い温度範囲にPTCサーミスタを自己発熱させる電圧が適
宜選択される。DETAILED DESCRIPTION OF THE INVENTION [Industrial range of use] The present invention relates to a novel method for detecting a change in heat ray intensity due to a minute heat ray such as movement of a human body or the presence or absence of a heated object. [Conventional Technology and Problems] Conventionally, as a method for detecting a change in heat ray intensity using a thermistor, NTC (Negative Temperature Coeffi) composed of a complex oxide of manganese, cobalt, iron, copper and transition metal is used.
cient) Thermistor method has been put to practical use. This method detects the change in the heat wire intensity by measuring the change in the current flowing through the NTC thermistor by utilizing the increase in the conductivity with respect to the increase in the heat wire intensity of the NTC thermistor. However, while the NTC thermistor has the advantage that it can be used at room temperature, the temperature coefficient of resistance (α) is generally -4%.
It had a problem that the measurement sensitivity was low, as low as about / ° C. On the other hand, a PTC (Positive Temperature Coefficient) thermistor is known as a thermistor having characteristics opposite to those of the NTC thermistor. This PTC thermistor generally has a composition based on barium titanate.
The thermistor has an extremely large temperature coefficient of resistance of 15-100% / ° C within the temperature range where PTC characteristics are shown (hereinafter referred to as the PTC range). Therefore, it is possible to detect changes in heat rays with high sensitivity by using the PTC thermistor. However, since the PTC region of PTC thermistors is generally higher than the operating environment temperature, it was necessary to adjust the temperature of the PTC thermistor to such a temperature region. Heretofore, several methods have been reported for measuring the intensity change of heat rays using a PTC thermistor. For example, JERalph, ln
frared Phys., 22 , 245 (1982). Describes a method of measuring a change in current value by applying a minute voltage for measurement to the PTC thermistor while heating the PTC thermistor to a constant temperature by an external heater. However, it is difficult for the above measurement method to keep the temperature of the PTC thermistor constant. In particular, the temperature of the PTC thermistor hunts for a long time due to changes in the ambient temperature when the device is used. Therefore, there is a problem that the current value (initial value) when the heat ray is not working is not stable and an error easily occurs in the detection of the heat ray. Also, as a means for solving the above problems in heating,
A method of using a PTC thermistor having a PTC region in the operating environment temperature is conceivable. Generally, a PTC thermistor having such characteristics has a small temperature coefficient of resistance, and the resistance value changes by several orders of magnitude due to changes in the operating environment temperature. The problem is that matching is difficult when using an amplifier. Due to the above problems, the technology for detecting heat rays using a PTC thermistor has not yet been put to practical use. [Means for Solving Problems] The inventors of the present invention have conducted extensive studies to use a PTC thermistor having a large temperature coefficient of resistance for detecting heat rays. As a result, P
By utilizing the constant temperature exothermicity of the TC thermistor, it is possible to control the temperature stably within the PTC region of the PTC thermistor, and the PTC thermistor has good performance even when a voltage is applied to the PTC thermistor that causes self-heating. The inventors have found that the sensitivity can be further increased by exhibiting the response speed and the sensitivity, and particularly by setting the voltage for causing the PTC thermistor to self-heat within a specific range, and completed the present invention. According to the present invention, when a PTC thermistor is used to detect a heat ray, a voltage that self-heats in a temperature range above the temperature at which the temperature coefficient of resistance of the PTC thermistor changes from negative to positive and above the ambient temperature by 2 ° C or more is used. It is a method of detecting heat rays, which is characterized by detecting the change in the current flowing through the PTC thermistor while applying it. In the present invention, known materials are used for the PTC thermistor without any particular limitation. As an example of a typical PTC thermistor, barium titanate (BaTiO 3 ) is the main component, and a small amount of elements with different valences is added to this to make it a semiconductor, and barium titanate-based PTC thermistor, carbon is dispersed in urethane resin. Carbon / urethane resin-based PTC thermistor, Ti
Examples include metal oxide / polymer PTC thermistors in which metal oxides such as O, TiO 2 , VO 2 and V 2 O 3 are dispersed in polymers such as methacrylic acid polymers. Among these, a barium titanate-based PTC thermistor that exhibits a large positive resistance temperature characteristic and has stable characteristics is particularly preferably used. The above barium titanate-based PTC thermistor is a ceramic that is made into a valence controlled semiconductor by adding a trace amount of elements with different valences. For example, rare earth elements such as La and Ce are known to replace Ba sites, and elements such as Sb, Bi and Nb are known to replace Ti sites. It is recommended to add 0.05 to 0.4 mol% of these elements.
It is preferably used to make a TC thermistor a semiconductor. In addition, the PTC region of PTC thermistors with a composition based on barium titanate can be changed from -150 ° C to 4 ° C by changing the PTC region of the PTC thermistor with an additive called a shifter.
It can be changed continuously up to 00 ℃. For example, in order to detect weak heat rays such as human body detection, it is preferable to lower the PTC region to around room temperature in order to improve the sensitivity of the device. Also, in hot wire measurement at high temperatures, the PTC region may be set higher than the operating environment temperature in order to keep the temperature of the element constant. The element added to shift the PTC region is not particularly limited. For example, Pb is preferably used as a shifter for shifting the PTC region to a high temperature, and Sr, Sn, Zr is preferably used as a shifter for shifting the PTC region to a low temperature. Furthermore, various additives can be added to improve the properties of the barium titanate PTC thermistor. For example, in order to improve resistance temperature characteristics, Mn, Cr,
It is preferable to add 0.01 to 0.125 mol% of elements such as Fe. In the PTC thermistor used in the present invention, the higher the resistance temperature coefficient is, the more the sensitivity and the stability of the element temperature are improved. Therefore, it is preferable that the PTC thermistor has a resistance temperature coefficient of 10% / ° C. or more at the used element temperature. In addition, in order to make the particle size of the sintered compact uniform, keep the resistance low, and improve the withstand voltage characteristics, C
It is preferable to replace a with 3 to 5 mol%, Sr with 1 to 30 mol%, and Pb with 1 to 50 mol% Ba. Further, in order to improve the sinterability during sintering, it is preferable to add 0.5 to 5 mol% of an auxiliary agent such as SiO 2 , TiO 2 , and Al 2 O 3 which causes liquid phase sintering. In the present invention, the size of the PTC thermistor may be appropriately determined, but it is preferable that the PTC thermistor be formed in a thin film having a thickness of 1 to 200 μm in order to uniformly generate self-heating by applying a voltage. FIG. 1 shows a typical structure of a PTC thermistor used in the present invention. 1 is a PTC thermistor, 1-a is an electrode,
1-b is a lead wire. In the present invention, the voltage applied to the PTC thermistor is not particularly limited as long as it is a voltage required to cause the PTC thermistor to self-heat in the PTC region and at a temperature higher by 2 ° C. or more than the operating environment temperature. Generally, the temperature at which the PTC thermistor begins to show PTC characteristics, that is, the temperature at which the temperature coefficient of resistance of the PTC thermistor changes from negative to positive (hereinafter referred to as Tf) or higher, and below the temperature at which the PTC thermistor exhibits maximum resistance (hereinafter referred to as Tm) The voltage that causes the PTC thermistor to self-heat in the range of 2) and the PTC thermistor to self-heat in the temperature range that is higher than the operating environment temperature by 2 ° C or more is appropriately selected. Especially above Tf, Tf +
The voltage that causes the PTC thermistor to self-heat in the temperature range of (Tm-Tf) / 2 or less and 2 ° C or more higher than the operating environment temperature is appropriately selected.
上記電圧を印加するための電源としては，直流電源が一
般的に使用される． また，使用環境温度の変化によるPTCサーミスタの温度
の変化を抑え，より精度良く熱線を検出するためには,V
I＝Ｇ（Ｔ−Ta）の関係式に基づき印加する電圧を調節
することで,PTCサーミスタの温度を一定に保つことがで
きる．ここで,Vは印加電圧（Ｖ）,Iは素子に流れる電流
（Ａ）,GはPTCサーミスタの熱放散係数（W/℃）,TはPTC
サーミスタの温度（℃）,Taは使用環境温度（℃）であ
る． 本発明において,PTCサーミスタに流れる電流変化の検出
方法は特に制限されない．例えば，第２図に示すように
PTCサーミスタ１に流れる電流を電流計２で直接測定
し，該電流値の差を見ることにより検出する方法があ
る．なお，図において３は電源,4はアースである．ま
た，他の方法として，第３図に示すようにPTCサーミス
タ１と直列に接続される抵抗５にかかる電圧を電圧計６
で測定し，該電圧の変化を検出する方法，第４図に示す
ように,PTCサーミスタ１と抵抗7,8及び９とによりホイ
ストンブリッジ回路を構成し，該回路に発生する電圧を
電圧計６で測定することにより，間接的にPTCサーミス
タに流れる電流の変化を検出する方法などが挙げられ
る． また，上記電流変化の検出において，増幅器を使用する
ことも特に制限されない． さらに，検出された電流変化は，如何なる方法で出力し
ても良い．例えば，記録計，電流計，ライトのオンオ
フ，あるいは電気機器のスイッチング等が挙げられる． 本発明の方法は，一般にPTCサーミスタを１つ使用して
実施することが可能であるが，第５図に示すように，直
列に接続した２つの同一の特性を有するPTCサーミスタ
１および1'と抵抗10及び11とによりブリッジ回路を構成
し，一方のPTCサーミスタ1'を熱線から遮断するカバー1
2を取り付けた装置を用い，該ブリッジ回路に発生する
電圧を電圧計６で測定することにより行うこともでき
る．かかる方法によれば,2つのPTCサーミスタの使用に
よって，使用環境温度の変化による影響を相殺すること
ができ，精度よく熱線を検出することができる． ［効果］ 本発明の熱線検出方法は,PTCサーミスタに電圧を印加
し，該PTCサーミスタのPTC領域内の温度で且つ使用環境
温度よりも２℃以上高い温度範囲に自己発熱させること
により，高感度でかつ速い応答速度で熱線を検出するこ
とが可能である．また，外部ヒーターを使用することな
く,PTCサーミスタをPTC領域に加熱して熱線を検出でき
るため装置が簡略化できる．さらに，使用環境温度が変
化しても，一定の温度に素子温度を調節することが可能
であるため抵抗温度係数の大きなPTCサーミスタとして
使用でき，増幅器とのマッチングを向上させることもで
きる． 本発明の熱線検出方法は，特に微小な熱線の検出，例え
ば人体等から放射される熱線の検出に有効である． ［実施例］ 以下，実施例によって本発明を具体的に説明するが，本
発明はこれらの実施例に限定されるものではない． 実施例１ Ba0.621Sr0.336Ca0.040La0.003TiO3＋0.02mo1％SiO2と
なるようにBaCO3'SrCO3'La(NO3)3・4H20,TiO2（ルチル）
を所定量それぞれ秤量し，ポリエチレンポットおよびジ
ルコニア製ボールを用いて湿式混合した．これらの混合
物を1000℃で２時間仮焼した後,Mn(NO3)2・6H2Ｏを0.05m
ol％となるように乳鉢を用いて混合し,400℃で硝酸マン
ガンを分解させた．得られた粉末を200メッシュのふる
いを通した後，直径1cmの金型を用いて,700Kg/cm2で成
形した．この成形体を1350℃で２時間焼結した．昇温速
度は400℃/Hr,冷却速度は100℃/Hrである．キュリー温
度は15℃であった． 得られた焼結体を切り出し，第１図に示すような構造の
PTCサーミスタを作成した．第１図中，上記方法で得ら
れた焼結体を切り出したPTCサーミスタ１は,5mm×2mm×
100μｍの大きさである.1−ａの電極は，オーミック性
銀ペースト（Dometoron社製,61900781/347）をリード線
１−ｂと共にPTCサーミスタと焼き付けた．尚PTCサーミ
スタの表面温度の測定は，シアノアクリレート系接着剤
（東亜合成化学社製，アロンアルファ）でPTCサーミス
タ表面に取り付けた微小サーミスタ（芝浦電子製,PT5−
25E5）を用いた． 第２図に示した回路に上記PTCサーミスタを組み込んだ
装置を用いて,600℃の黒体炉から放射される熱線を照射
したときの,PTCサーミスタの応答を調べた．尚，黒体炉
と素子間の距離は10cmとし，外気温は17℃であった．素
子温度を30℃に保つために必要な電圧16.6Vを印加し，
熱線照射前後の電流値を第１表に示す時間ごとに測定し
た．熱線照射前の電流値，及び照射時の電流変化を第１
表に併せて示す． 上記結果より明らかなように，本発明の方法によれば電
圧印加直後から熱線照射前の電流値が一定となり,PTCサ
ーミスタの温度が安定していることがわかる．また，照
射時の電流変化も電圧印加直後から一定であり，安定し
た熱線検出特性を有していることがわかる． 比較例１ 実施例１において，印加電圧を1.0Vとし,PTCサーミスタ
をゴールドファーネスで外部加熱して，該PTCサーミス
タの温度を30℃に調節した以外は同様にして，熱線照射
前後の電流値を時間ごとに測定した．熱線照射前の電流
値及び照射時の電流変化を第２表に示す． 上記結果から明らかなように外部から加熱した場合に
は，熱線照射前の電流値の変動が大きく，安定した素子
温度制御が行えていないことがわかる．また，熱線照射
時の電流変化も変動が大きく，安定した熱線検出特性が
得られない． 実施例２ 実施例１と同様の方法でBa0.997La0.003TiO3＋2mol％Si
O2＋0.07mol％MnOなる組成を有するPTCサーミスタを作
成した．キュリー点は122℃であった． 第４図に示した回路に上記PTCサーミスタを組み込んだ
装置を用いて,600Kの黒体炉から放射される熱線を照射
したときのPTCサーミスタの応答を調べた．第４図の抵
抗８は可変抵抗器を用いPTCサーミスタと等しい抵抗と
した．また，抵抗7,9はそれぞれ1kΩとした．尚，黒体
炉とPTCサーミスタとの距離は10cmとし，外気温は15℃
であった． 上記測定装置を用い，第３表に示すような電圧を印加し
たときのPTCサーミスタの表面温度，熱線照射時にブリ
ッジ回路に発生する電圧，及び熱時定数を測定した．こ
れらの結果，及びブリッジ回路に発生する電圧を1Wあた
りの熱線に換算した値（電圧感度）を第３表に併せて示
す． 上記結果より明らかなように，印加電圧を30V以上とす
ることでPTCサーミスタをPTC特性を有する温度領域に加
熱することができることがわかる．また30V未満の電圧
を印加したときと比較して発生電圧が大きくなり，入射
熱線1W当りにブリッジ回路に発生する電圧（電圧感度）
に換算すると100V/Wを越え，高感度に熱線を検出できる
ことがわかる． また,PTCサーミスタがPTC領域に加熱されると熱時定数
が小さくなり，応答速度が向上することがわかる． 実施例３ 実施例２のPTCサーミスタを第２図に示す回路に組み込
んだ測定装置を用いて,PTCサーミスタの温度を122℃に
保つために50Vの電圧を印加し，熱線照射前後の電流変
化を第４表に示す時間ごとに測定した．実施例１と同様
に，熱線照射前の電流値及び照射時の電流変化を第４表
に併せて示す． 上記結果より明らかなように，本発明の方法によれば電
圧印加直後から熱線を照射しないときの電流一定とな
り,PTCサーミスタの温度が安定していることがわかる．
また，照射時の電流変化も電圧印加直後から一定であ
り，安定した熱線検出特性を有していることがわかる． A DC power supply is generally used as a power supply for applying the above voltage. In addition, in order to suppress the change in temperature of the PTC thermistor due to the change in operating environment temperature and detect the heat rays more accurately, V
The temperature of the PTC thermistor can be kept constant by adjusting the applied voltage based on the relational expression of I = G (T-Ta). Where V is the applied voltage (V), I is the current flowing through the element (A), G is the heat dissipation coefficient (W / ℃) of the PTC thermistor, and T is the PTC.
The thermistor temperature (° C) and Ta are the operating environment temperatures (° C). In the present invention, the method of detecting changes in the current flowing through the PTC thermistor is not particularly limited. For example, as shown in Figure 2.
There is a method in which the current flowing in the PTC thermistor 1 is directly measured by the ammeter 2 and the difference in the current value is observed to detect it. In the figure, 3 is the power supply and 4 is the ground. As another method, as shown in FIG. 3, the voltage applied to the resistor 5 connected in series with the PTC thermistor 1 is measured by a voltmeter 6.
A method for detecting changes in the voltage by means of a PTC thermistor 1 and resistors 7, 8 and 9 as shown in FIG. There is a method of indirectly detecting the change in the current flowing in the PTC thermistor by measuring with 6. In addition, the use of an amplifier is not particularly limited in detecting the current change. Furthermore, the detected current change may be output by any method. Examples include recorders, ammeters, lights on / off, and switching of electrical equipment. Generally, the method of the present invention can be carried out using one PTC thermistor, but as shown in FIG. 5, two PTC thermistors 1 and 1'having the same characteristics connected in series are used. A cover 1 that forms a bridge circuit with resistors 10 and 11 and shuts off one PTC thermistor 1'from heat rays
It is also possible to use a device equipped with 2 and measure the voltage generated in the bridge circuit with a voltmeter 6. According to such a method, the use of two PTC thermistors can cancel the influence of the change in the operating environment temperature, and the heat ray can be detected accurately. [Effect] The method of detecting heat rays of the present invention has high sensitivity by applying a voltage to the PTC thermistor and causing the PTC thermistor to self-heat within a temperature range within the PTC region of the PTC thermistor and at least 2 ° C higher than the ambient temperature. It is possible to detect heat rays with high response speed. In addition, the PTC thermistor can be heated in the PTC region to detect heat rays without using an external heater, which simplifies the system. Furthermore, even if the operating environment temperature changes, the element temperature can be adjusted to a constant temperature, so it can be used as a PTC thermistor with a large resistance temperature coefficient, and the matching with the amplifier can be improved. The heat ray detection method of the present invention is particularly effective for detecting minute heat rays, for example, heat rays radiated from a human body or the like. [Examples] Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples. Example 1 Ba 0.621 Sr 0.336 Ca 0.040 La 0.003 TiO 3 + 0.02mo1% SiO 2 and so as to BaCO 3 'SrCO 3' La ( NO 3) 3 · 4H 2 0, TiO 2 ( rutile)
Were weighed in predetermined amounts and wet-mixed using a polyethylene pot and zirconia balls. After the mixtures were calcined for 2 hours at 1000 ° C., 0.05 m and Mn (NO 3) 2 · 6H 2 O
The mixture was mixed using a mortar so that the ol% was reached, and manganese nitrate was decomposed at 400 ° C. The obtained powder was passed through a 200-mesh sieve and then molded at 700 Kg / cm 2 using a mold with a diameter of 1 cm. This compact was sintered at 1350 ° C for 2 hours. The heating rate is 400 ° C / Hr and the cooling rate is 100 ° C / Hr. The Curie temperature was 15 ° C. The obtained sintered body was cut out and made into a structure as shown in Fig. 1.
Created a PTC thermistor. In Fig. 1, the PTC thermistor 1 obtained by cutting out the sintered body obtained by the above method is 5 mm × 2 mm ×
The size of 100 μm. The electrode of 1-a was formed by baking an ohmic silver paste (manufactured by Dometoron, 61900781/347) together with a lead wire 1-b and a PTC thermistor. The surface temperature of the PTC thermistor was measured using a cyanoacrylate adhesive (Toagosei Kagaku Co., Ltd., Aron Alpha) attached to the surface of the PTC thermistor.
25E5) was used. Using the device in which the above PTC thermistor was incorporated in the circuit shown in Fig. 2, the response of the PTC thermistor when irradiated with heat rays emitted from a blackbody furnace at 600 ° C was investigated. The distance between the blackbody furnace and the element was 10 cm, and the outside air temperature was 17 ° C. Apply the voltage 16.6V necessary to keep the element temperature at 30 ℃,
The current value before and after the heat ray irradiation was measured at each time shown in Table 1. First, the current value before the heat ray irradiation and the current change during the irradiation
It is also shown in the table. As is clear from the above results, according to the method of the present invention, the current value is constant immediately after the voltage application and before the heat ray irradiation, and the temperature of the PTC thermistor is stable. In addition, it can be seen that the current change during irradiation is constant immediately after the voltage is applied, and that it has stable heat ray detection characteristics. Comparative Example 1 In Example 1, the applied voltage was set to 1.0 V, the PTC thermistor was externally heated by a gold furnace, and the temperature of the PTC thermistor was adjusted to 30 ° C. It was measured every hour. Table 2 shows the current value before the heat ray irradiation and the current change during the irradiation. As is clear from the above results, when heating from the outside, there is a large fluctuation in the current value before irradiation with heat rays, and stable element temperature control cannot be performed. In addition, the change in current during heat ray irradiation also fluctuates greatly, and stable heat ray detection characteristics cannot be obtained. Example 2 In the same manner as in Example 1, Ba 0.997 La 0.003 TiO 3 +2 mol% Si
A PTC thermistor having a composition of O 2 +0.07 mol% MnO was prepared. The Curie point was 122 ° C. The response of the PTC thermistor when irradiated with heat rays emitted from a 600K blackbody furnace was examined by using the device in which the above PTC thermistor was incorporated in the circuit shown in Fig. 4. The resistor 8 in Fig. 4 uses a variable resistor and has the same resistance as the PTC thermistor. The resistors 7 and 9 were each 1 kΩ. The distance between the blackbody furnace and the PTC thermistor was 10 cm, and the outside air temperature was 15 ° C.
Met. Using the above measuring device, the surface temperature of the PTC thermistor when a voltage as shown in Table 3 was applied, the voltage generated in the bridge circuit at the time of heat ray irradiation, and the thermal time constant were measured. Table 3 also shows these results and the value (voltage sensitivity) in which the voltage generated in the bridge circuit is converted into heat rays per 1W. As is clear from the above results, it can be seen that the PTC thermistor can be heated to a temperature range having PTC characteristics by setting the applied voltage to 30 V or higher. In addition, the generated voltage is greater than when a voltage of less than 30 V is applied, and the voltage generated in the bridge circuit per 1 W of incident heat wire (voltage sensitivity)
It can be seen that when converted to, the heat ray exceeds 100 V / W and the heat ray can be detected with high sensitivity. It is also found that when the PTC thermistor is heated in the PTC region, the thermal time constant becomes smaller and the response speed improves. Example 3 Using the measuring device in which the PTC thermistor of Example 2 is incorporated in the circuit shown in FIG. 2, a voltage of 50 V is applied to keep the temperature of the PTC thermistor at 122 ° C. It was measured at each time shown in Table 4. As in Example 1, Table 4 also shows the current value before the heat ray irradiation and the current change during the irradiation. As is clear from the above results, according to the method of the present invention, the current becomes constant immediately after the voltage is applied and no heat ray is applied, and the temperature of the PTC thermistor is stable.
In addition, it can be seen that the current change during irradiation is constant immediately after the voltage is applied, and that it has stable heat ray detection characteristics.
【図面の簡単な説明】 第１図は本発明の方法に用いられるPTCサーミスタの構
造の一例を示す図である． 第２図，第３図，第４図，及び第５図は本発明を実施す
るための回路の代表的な態様図である． また，図において,1,1'はPTCサーミスタ,1−ａは電極,1
−ｂはリード線,2は電流計,3は電源,4はアース,5は抵抗
器,6は電圧計,7,8,9,10,11は抵抗器,12は熱線を遮蔽す
るカバーを示す．BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an example of the structure of a PTC thermistor used in the method of the present invention. 2, 3, 4, and 5 are typical mode diagrams of circuits for carrying out the present invention. In the figure, 1,1 'is a PTC thermistor, 1-a is an electrode, 1
-B is a lead wire, 2 is an ammeter, 3 is a power supply, 4 is ground, 5 is a resistor, 6 is a voltmeter, 7,8,9,10,11 are resistors, and 12 is a cover for shielding heat rays. Show.