JP3893475B2 - Thermoelectric element figure of merit measuring apparatus and measuring method - Google Patents

Thermoelectric element figure of merit measuring apparatus and measuring method Download PDF

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JP3893475B2
JP3893475B2 JP2001196416A JP2001196416A JP3893475B2 JP 3893475 B2 JP3893475 B2 JP 3893475B2 JP 2001196416 A JP2001196416 A JP 2001196416A JP 2001196416 A JP2001196416 A JP 2001196416A JP 3893475 B2 JP3893475 B2 JP 3893475B2
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thermoelectric element
merit
component
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voltage
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JP2003014804A (en
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幹夫 小矢野
秀夫 岩崎
秀信 堀
精二郎 佐野
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Japan Advanced Institute of Science and Technology
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Japan Advanced Institute of Science and Technology
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Description

【０００１】
【発明の属する技術分野】
本発明は、熱電素子の性能指数を測定する測定装置及び測定方法に関する。
【０００２】
【従来の技術】
従来から、熱電素子の性能指数を測定する方法が知られており、例えば特開平１−１６１１４０号公報に示されている。図４は、同公報に開示された測定方法の説明図を表しており、以下図４に基づいて従来技術を説明する。
図４において、被測定物である熱電素子２の両端には、良導体からなる電極３，３が、熱電素子２の端面全体を覆うように接合されている。それぞれの電極３，３には、電圧を測定するためのリード線４Ａ及び電流を測定するためのリード線４Ｂが接続されている。
熱電素子２両端部の電極３，３には、それぞれ熱電対５が接触している。これにより、熱電素子２両端部の温度を測定している。熱電素子２は、１０-2Ｐａ以下の高真空中に置かれる。
【０００３】
前記公報に記載された測定手順は、次の通りである。
１）電極３，３間に直流電流を流し、定常状態になった後、電極３，３間の電圧、電流、及び温度を測定する。
２）電極３，３間に、実効値が、１）で流した直流電流値にほぼ等しい交流電流を流し、定常状態になった後、電極３，３間の電圧、電流、及び温度を測定する。
こうして得られた測定値を、所定の式に代入して、熱電素子２の性能指数Ｚを求めている。
【０００４】
【発明が解決しようとする課題】
しかしながら、前記従来技術には、次に述べるような問題がある。
即ち従来技術によれば、まず熱電素子２に直流電流を流して電圧など所定のパラメータの測定を行ない、その後、交流電流を流して、さらにパラメータの測定を行なっている。そのため、測定に時間がかかる。
これに加え、交流電流を熱電素子２に流した場合にはジュール熱が発生するが、熱電素子２内部の温度は均一になる。ところが、直流電流を熱電素子２に流した場合には、ペルチェ効果によって、熱電素子２内部の温度に不均一が生じる。
その結果、直流電流を流した場合と、交流電流を流した場合とでは、熱電素子２が熱平衡に達した時点での内部の熱分布が異なることになる。熱電素子２の性能指数Ｚを求める関係式は、交流電流を流したときと直流電流を流したときとで、熱電素子２内部の温度分布が同じである場合に成り立つ。その結果、温度分布の変動によって、計測結果に誤差が生じ、性能指数Ｚが不正確となる。
このような不正確さを補正するためには、例えば、被測定物である熱電素子２の形状を、熱分布の相違が生じにくいものにする必要があり、測定方法を任意の形状の熱電素子２に応用するのが困難となる。
【０００５】
本発明は、上記の問題に着目してなされたものであり、短い測定時間で熱電素子の性能指数を正確に測定可能な、熱電素子の性能指数測定装置及び測定方法を提供することを目的としている。
【０００６】
【課題を解決するための手段、作用及び効果】
上記の目的を達成するために、本発明は、
熱電素子の両端部間に電流を流し、その両端部間の電圧を測定して無次元性能指数を測定する熱電素子の性能指数測定装置において、
熱電素子に交流電流を流す交流電流源と、
熱電素子に交流電流と同時に直流電流を流す直流電流源と、
熱電素子の両端部にかかる電圧の、交流成分の振幅を測定する交流電圧計と、
熱電素子の両端部にかかる電圧の、直流成分を測定する直流電圧計とを備え、
同時に測定した前記電圧の交流成分の振幅及び直流成分に基づいて、性能指数を求めている。
かかる構成によれば、交流電流と直流電流とを同時に流すことにより、電圧の交流成分測定時と直流成分測定時とで、被測定物である熱電素子の温度分布が同一になる。従って、性能指数の測定が正確になる。
【０００７】
また本発明によれば、
交流電流の振幅と、
直流電流の電流値とを略同一にしている。
かかる構成によれば、熱電素子の電圧の交流成分の振幅及び直流成分のみを計測するだけで、無次元性能指数を求めることが可能となり、計測が簡略化される。
【０００８】
また、本発明によれば、
熱電素子を略一定の温度に保つ、恒温装置を備えている。
かかる構成によれば、熱電素子の熱リークがほぼ０になることから、計測時に熱リークの影響を排除でき、計測が正確になる。
【０００９】
また、本発明によれば、
熱電素子の温度を測定する温度センサを備え、
熱電素子内部の温度が平衡に達したことを検知し、
温度平衡時の熱電素子の温度を測定し、
前記交流電圧、直流電圧、及び温度に基づいて、性能指数を求めている。
かかる構成によれば、無次元性能指数と同様に、性能指数を正確に求めることも可能である。
【００１０】
【発明の実施の形態】
以下、図を参照しながら、本発明に係る実施形態を詳細に説明する。
図１は、本実施形態に係る性能指数測定装置１のブロック図を示している。図１において、熱電素子２の両端部には、良導体の電極３，３が接合されている。電極３，３の材質としては、銀、銅、ニッケル等が好適である。
性能指数測定装置１は、被測定物である熱電素子２に、交流電流ＩACを流す交流電流源７と、直流電流ＩDCを流す直流電流源８とを備えている。交流電流源７及び直流電流源８は、出力側がいずれも電極３，３の一側に接続されている。また、電極３，３の他側は、アース電位に接地されており、熱電素子２には、（ＩAC＋ＩDC）なる電流が流れるようになっている。
【００１１】
また、性能指数測定装置１は、熱電素子２の両端部の電極３，３に密に接触した、例えば熱電対５等の温度センサを備えている。熱電対５は、熱伝導率の良い電極３，３に貼りつけられ、熱電素子２の両端部近傍の温度を精密に測定することが可能である。
さらに性能指数測定装置１は、熱電素子２の両端部の電圧の交流成分ＶACを測定する交流電圧計９と、電圧の直流成分ＶDCを測定する直流電圧計１０とを備えている。
交流電圧計９は、電圧の微少な交流成分を測定する必要があり、例えばロックインアンプが好適である。交流電圧計９と交流電流源７との間は、電気的に接続されており、同期を取るために、交流電圧計９から交流電流源７に対して、リファレンス信号Ｓが送られる。
交流電流源７、直流電流源８、交流電圧計９、直流電圧計１０、及び熱電対５は、いずれもコントローラ２０に電気的に接続されている。コントローラ２０は、性能指数測定装置１を制御し、性能指数Ｚの測定を行なう。
【００１２】
図２に、性能指数測定装置１の詳細な構成図を示す。
図２において、性能指数測定装置１は、被測定物である熱電素子２の温度を一定に保ち、熱電素子２から熱のリークが無いようにする恒温装置６を備えている。恒温装置６は、熱電素子２を内部に入れる内室１１と、内室１１を囲繞する外室１２とを備えている。外室１２及び内室１１は、熱伝導率のなるべく良い材料で構成されていることが望ましく、例えば銅などの金属が好適である。
外室１２は、液体寒剤１５に浸漬されている。液体寒剤１５としては、温度（４．２Ｋ）の低い液体Ｈｅが最も好ましいが、液体窒素（温度７７．３Ｋ）でもよい。外室１２の周囲には外側ヒータ１４が、内室１１の周囲には内側ヒータ１３が、それぞれ巻かれている。
外室１２の外側が、液体寒剤１５の温度と略同一になっているのに対し、内室１１の内部は、ヒータ１３，１４によって室温程度に保たれている。
内室１１の内部及び外室１２の内部は、真空ポンプ１６により、約１０-3Ｐａ以下の高真空に排気されている。これにより、対流による熱損失を少なくし、内室１１の内部及び熱電対５の温度が変動しないようにしている。
【００１３】
図２に示すように熱電素子２は、絶縁性の糸１７により、内室１１の内部に吊るされている。この絶縁性の糸１７は、低温になっても収縮しない材質が好ましく、例えば木綿糸１７が好適である。
熱電素子２の両端部の電極３，３には、電流源７，８及び電圧計９，１０に電気的に接続するためのリード線１８とが、接続されている。リード線１８としては、外室１２外部からの熱の侵入を防止するため、なるべく細いものが望ましく、直径５０μｍ程度の、リン青銅線が好適である。
リード線１８は、内室１１の内壁に付設されたサーマルアンカ１９に何重にか巻かれた後、真空を封止する図示しない電流導入端子を介して、外部と電気的に接続されている。サーマルアンカ１９は、例えば銅などの円柱であり、一端部が内室１１の内壁に接触している。これにより、リード線１８を伝わって外部から侵入した熱が、サーマルアンカ１９を介して内室１１内壁へと拡散し、熱電素子２に熱が伝わることが非常に少なくなる。
【００１４】
次に、このような性能指数測定装置１を用いて、無次元化された性能指数ＺＴを測定する手順について、説明する。
まず、交流電流源７及び直流電流源８から、熱電素子２の両端部間に、それぞれ交流電流ＩAC及び直流電流ＩDCを流す。このとき、交流電流ＩACがｂcosωｔで、直流電流ＩDCがａでそれぞれ表されるとすると、ａ＝ｂとなるように電流を流す。これにより、熱電素子５を流れる電流は、交流電流ＩACと直流電流ＩDCとの和ＩAC＋ＩDCとなり、図３のようにａ＋ｂcosωｔで表される。このとき、横軸が時間であり、縦軸が電流値である。
尚、ωは、交流電流ＩACの周波数であり、交流電流ＩACを熱電素子２に流した際にペルチェ効果による熱の発生を妨げるため、充分大きな値であることが必要であり、例えば１０Ｈzよりも大きいことが好ましい。
【００１５】
温度変動が殆んどなくなった状態の熱電素子２においては、ａ＝ｂの条件下で次の数式１が成り立つ。
ＺＴ＝（１／ｘ）｛（ＶDC／ＶAC0）−１｝ ………… （１）
このとき、ｘは熱リークを示す定数であり、外部への熱リークがまったくないと仮定すると、ｘ＝１となる。また、ＶAC0は、熱電素子２の電気抵抗をＲとした場合のｂ・Ｒに相当し、電圧の交流成分の振幅を示している。
即ち、電圧の交流成分の振幅ＶAC0と直流成分ＶDCとを測定することにより、無次元性能指数ＺＴが求められる。但し、この数式１は、電圧の直流成分ＶDCの測定時と、交流成分の振幅ＶAC0の測定時とで、熱電素子２において温度Ｔの変化があると成り立たないことも知られている。
【００１６】
従ってコントローラ２０は、熱電対５の出力に基づき、熱電素子２の温度Ｔの変動が殆んどなくなったことを検知する。そして、交流電圧計９及び直流電圧計１０によって、熱電素子２の両端部間の電圧の交流成分の振幅ＶAC0及び直流成分ＶDCを、それぞれ測定する。そして、これらの値ＶAC0，ＶDCを、数式１に代入することにより、無次元性能指数ＺＴを求めている。
また、コントローラ２０は、熱電対５によって熱電素子２の平均温度Ｔ0を精密に測定し、数式１に平均温度Ｔ0を代入して、性能指数Ｚを求めることも可能である。
【００１７】
以上説明したように、本実施形態によれば、熱電素子２に交流電流ＩACと直流電流ＩDCとを同時に流している。そして、熱電素子２の温度Ｔが定常状態に達したときの電圧の交流成分の振幅ＶAC0及び直流電圧ＶDCに基づいて、熱電素子２の性能指数ＺＴを検出している。このように、交流電流ＩACと直流電流ＩDCとを熱電素子２に同時に流すことにより、従来技術のように、交流電流を流したときと直流電流とを流したときで、熱電素子２の内部の熱分布が変化しない。
上述したように数式１は、電圧の交流成分の振幅ＶAC0測定時と直流成分ＶDCの測定時とで、温度変化がない場合にのみ成り立つ。従って、本実施形態のように、交流電流ＩACと直流電流ＩDCとを同時に流すことにより、精密な測定が可能である。
【００１８】
また、交流電流ＩAC（＝ｂcosωｔ）と直流電流ＩDC（＝ａ）とを同時に流すことにより、交流電流ＩACの振幅ｂと、直流電流ＩDCの値ａとを厳密に一致させることが可能である。数式１は、ａ＝ｂの時にのみ成り立つので、これを厳密に一致させることにより、より正確な性能指数の測定が可能である。
【００１９】
また、本実施形態の性能指数測定装置１によれば、液体寒剤１５を用い、内部を真空にした恒温装置６の中に、熱電素子２を入れて計測を行なっている。これにより、熱電素子２が外部の温度変化の影響を受けず、熱的に安定した状態になるので、精密な測定が可能である。さらに、クライオポンプ効果により、熱リークが殆んどなくなるので、定数ｘがほぼ１となり、交流電流ＩAC及び直流電流ＩDCを測定するだけで、性能指数を正確に求めることができる。
【００２０】
尚、図２に示した恒温装置６は、内室１１と外室１２とを備えるように説明したが、その間に中間室を設け、３重又はそれ以上にしてもよい。これにより、さらに熱電素子の温度が安定になり、計測が正確になる。
【図面の簡単な説明】
【図１】実施形態に係る性能指数測定装置のブロック図。
【図２】性能指数測定装置の詳細な構成図
【図３】熱電素子を流れる電流を示すグラフ。
【図４】従来技術に係る性能指数測定装置のブロック図。
【符号の説明】
１：性能指数測定装置、２：熱電素子、３：電極、４：リード線１、５：熱電対、６：恒温装置、７：交流電流源、８：直流電流源、９：交流電圧計、１０：直流電圧計、１１：内室、１２：外室、１３：内側ヒータ、１４：外側ヒータ、１５：液体寒剤、１６：真空ポンプ、１７：糸、１８：リード線、１９：サーマルアンカ、２０：コントローラ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a measuring apparatus and a measuring method for measuring a figure of merit of a thermoelectric element.
[0002]
[Prior art]
Conventionally, a method for measuring a figure of merit of a thermoelectric element is known, and for example, disclosed in Japanese Patent Application Laid-Open No. 1-161140. FIG. 4 is an explanatory diagram of the measurement method disclosed in the publication, and the prior art will be described based on FIG.
In FIG. 4, electrodes 3 and 3 made of a good conductor are joined to both ends of a thermoelectric element 2 as an object to be measured so as to cover the entire end face of the thermoelectric element 2. Connected to each of the electrodes 3 and 3 is a lead wire 4A for measuring voltage and a lead wire 4B for measuring current.
The thermocouple 5 is in contact with the electrodes 3 and 3 at both ends of the thermoelectric element 2. Thereby, the temperature of the both ends of the thermoelectric element 2 is measured. The thermoelectric element 2 is placed in a high vacuum of 10 −2 Pa or less.
[0003]
The measurement procedure described in the publication is as follows.
1) A direct current is passed between the electrodes 3 and 3, and after a steady state is reached, the voltage, current and temperature between the electrodes 3 and 3 are measured.
2) An alternating current having an effective value approximately equal to the direct current value passed in 1) is passed between the electrodes 3 and 3, and after a steady state is reached, the voltage, current, and temperature between the electrodes 3 and 3 are measured. To do.
The performance index Z of the thermoelectric element 2 is obtained by substituting the measured value thus obtained into a predetermined equation.
[0004]
[Problems to be solved by the invention]
However, the prior art has the following problems.
That is, according to the prior art, first, a direct current is passed through the thermoelectric element 2 to measure a predetermined parameter such as a voltage, and then an alternating current is passed to further measure the parameter. Therefore, measurement takes time.
In addition, Joule heat is generated when an alternating current is passed through the thermoelectric element 2, but the temperature inside the thermoelectric element 2 becomes uniform. However, when a direct current is passed through the thermoelectric element 2, the temperature inside the thermoelectric element 2 becomes non-uniform due to the Peltier effect.
As a result, the internal heat distribution at the time when the thermoelectric element 2 reaches thermal equilibrium differs between when a direct current is passed and when an alternating current is passed. The relational expression for obtaining the figure of merit Z of the thermoelectric element 2 is established when the temperature distribution inside the thermoelectric element 2 is the same when an alternating current is passed and when a direct current is passed. As a result, a variation in temperature distribution causes an error in the measurement result, and the figure of merit Z becomes inaccurate.
In order to correct such inaccuracy, for example, it is necessary to make the shape of the thermoelectric element 2 that is the object to be measured difficult to cause a difference in heat distribution. 2 is difficult to apply.
[0005]
The present invention has been made paying attention to the above-mentioned problem, and aims to provide a thermoelectric element performance index measuring apparatus and a measurement method capable of accurately measuring the thermoelectric element performance index in a short measurement time. Yes.
[0006]
[Means, actions and effects for solving the problems]
In order to achieve the above object, the present invention provides:
In a performance index measuring device for a thermoelectric element that measures a dimensionless figure of merit by passing a current between both ends of the thermoelectric element and measuring a voltage between the both ends,
An alternating current source for passing an alternating current through the thermoelectric element;
A direct current source for supplying a direct current to the thermoelectric element simultaneously with an alternating current;
An AC voltmeter for measuring the amplitude of the AC component of the voltage applied to both ends of the thermoelectric element;
A DC voltmeter for measuring the DC component of the voltage applied to both ends of the thermoelectric element;
A figure of merit is obtained based on the amplitude and DC component of the AC component of the voltage measured simultaneously.
According to such a configuration, when the alternating current and the direct current are supplied simultaneously, the temperature distribution of the thermoelectric element that is the object to be measured becomes the same when measuring the alternating current component of the voltage and when measuring the direct current component. Thus, the figure of merit measurement is accurate.
[0007]
Also according to the invention,
The amplitude of the alternating current,
The current value of the direct current is substantially the same.
According to such a configuration, it is possible to obtain a dimensionless figure of merit simply by measuring the amplitude and direct current component of the alternating current component of the voltage of the thermoelectric element, and the measurement is simplified.
[0008]
Moreover, according to the present invention,
A thermostat is provided to keep the thermoelectric element at a substantially constant temperature.
According to such a configuration, since the heat leak of the thermoelectric element becomes almost zero, the influence of the heat leak can be eliminated at the time of measurement, and the measurement becomes accurate.
[0009]
Moreover, according to the present invention,
It has a temperature sensor that measures the temperature of the thermoelectric element,
Detects that the temperature inside the thermoelectric element has reached equilibrium,
Measure the temperature of the thermoelectric element at temperature equilibrium,
A figure of merit is determined based on the AC voltage, DC voltage, and temperature.
According to such a configuration, the performance index can be accurately obtained in the same manner as the dimensionless performance index.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a block diagram of a figure of merit measuring apparatus 1 according to the present embodiment. In FIG. 1, good conductor electrodes 3 and 3 are joined to both ends of a thermoelectric element 2. As a material of the electrodes 3 and 3, silver, copper, nickel or the like is preferable.
The figure of merit measurement device 1 includes an alternating current source 7 for supplying an alternating current IAC and a direct current source 8 for supplying a direct current IDC to a thermoelectric element 2 as a measurement object. The output sides of the AC current source 7 and the DC current source 8 are both connected to one side of the electrodes 3 and 3. The other sides of the electrodes 3 and 3 are grounded to the earth potential, and a current of (IAC + IDC) flows through the thermoelectric element 2.
[0011]
Further, the figure of merit measurement device 1 includes a temperature sensor such as a thermocouple 5 in close contact with the electrodes 3 and 3 at both ends of the thermoelectric element 2. The thermocouple 5 is attached to the electrodes 3 and 3 having good thermal conductivity, and the temperature in the vicinity of both end portions of the thermoelectric element 2 can be accurately measured.
Further, the figure of merit measurement device 1 includes an AC voltmeter 9 that measures the AC component VAC of the voltage at both ends of the thermoelectric element 2 and a DC voltmeter 10 that measures the DC component VDC of the voltage.
The AC voltmeter 9 needs to measure a minute AC component of voltage, and for example, a lock-in amplifier is suitable. The AC voltmeter 9 and the AC current source 7 are electrically connected, and a reference signal S is sent from the AC voltmeter 9 to the AC current source 7 for synchronization.
The AC current source 7, the DC current source 8, the AC voltmeter 9, the DC voltmeter 10, and the thermocouple 5 are all electrically connected to the controller 20. The controller 20 controls the performance index measuring apparatus 1 and measures the performance index Z.
[0012]
FIG. 2 shows a detailed configuration diagram of the performance index measuring apparatus 1.
In FIG. 2, the figure of merit measurement device 1 includes a thermostatic device 6 that keeps the temperature of the thermoelectric element 2 that is the object to be measured constant and does not leak heat from the thermoelectric element 2. The thermostatic device 6 includes an inner chamber 11 in which the thermoelectric element 2 is placed, and an outer chamber 12 that surrounds the inner chamber 11. The outer chamber 12 and the inner chamber 11 are preferably made of a material having as good a thermal conductivity as possible. For example, a metal such as copper is suitable.
The outer chamber 12 is immersed in the liquid cryogen 15. The liquid cryogen 15 is most preferably liquid He having a low temperature (4.2 K), but may be liquid nitrogen (temperature 77.3 K). An outer heater 14 is wound around the outer chamber 12, and an inner heater 13 is wound around the inner chamber 11.
The outside of the outer chamber 12 is substantially the same as the temperature of the liquid cryogen 15, while the inside of the inner chamber 11 is kept at about room temperature by the heaters 13 and 14.
The inside of the inner chamber 11 and the inside of the outer chamber 12 are evacuated to a high vacuum of about 10 −3 Pa or less by a vacuum pump 16. As a result, heat loss due to convection is reduced, and the temperature of the inside of the inner chamber 11 and the thermocouple 5 are prevented from fluctuating.
[0013]
As shown in FIG. 2, the thermoelectric element 2 is suspended inside the inner chamber 11 by an insulating thread 17. The insulating thread 17 is preferably made of a material that does not shrink even when the temperature is low, and for example, a cotton thread 17 is preferable.
The electrodes 3 and 3 at both ends of the thermoelectric element 2 are connected to current sources 7 and 8 and lead wires 18 for electrical connection to the voltmeters 9 and 10. The lead wire 18 is preferably as thin as possible in order to prevent heat from entering from the outside of the outer chamber 12, and a phosphor bronze wire having a diameter of about 50 μm is preferable.
The lead wire 18 is wound around a thermal anchor 19 attached to the inner wall of the inner chamber 11 several times, and then electrically connected to the outside through a current introduction terminal (not shown) that seals the vacuum. . The thermal anchor 19 is a cylinder such as copper, for example, and one end thereof is in contact with the inner wall of the inner chamber 11. As a result, heat that has entered through the lead wire 18 from the outside diffuses to the inner wall of the inner chamber 11 via the thermal anchor 19, and heat is hardly transmitted to the thermoelectric element 2.
[0014]
Next, a procedure for measuring the dimensionless figure of merit ZT using such a figure of merit measuring apparatus 1 will be described.
First, an alternating current IAC and a direct current IDC are passed between the both ends of the thermoelectric element 2 from the alternating current source 7 and the direct current source 8. At this time, if the alternating current IAC is represented by bcosωt and the direct current IDC is represented by a, the current is supplied so that a = b. As a result, the current flowing through the thermoelectric element 5 is the sum IAC + IDC of the alternating current IAC and the direct current IDC, and is represented by a + bcos ωt as shown in FIG. At this time, the horizontal axis is time, and the vertical axis is the current value.
Note that ω is the frequency of the alternating current IAC, and must be a sufficiently large value to prevent the generation of heat due to the Peltier effect when the alternating current IAC is passed through the thermoelectric element 2, for example, more than 10 Hz. Larger is preferred.
[0015]
In the thermoelectric element 2 with almost no temperature fluctuation, the following formula 1 is established under the condition of a = b.
ZT = (1 / x) {(VDC / VAC0) -1} (1)
At this time, x is a constant indicating a heat leak, and x = 1 assuming that there is no heat leak to the outside. VAC0 corresponds to b · R when the electric resistance of the thermoelectric element 2 is R, and indicates the amplitude of the AC component of the voltage.
That is, the dimensionless figure of merit ZT is obtained by measuring the amplitude VAC0 and the direct current component VDC of the alternating current component of the voltage. However, it is also known that Formula 1 does not hold when there is a change in the temperature T in the thermoelectric element 2 between the measurement of the DC component VDC of the voltage and the measurement of the amplitude VAC0 of the AC component.
[0016]
Therefore, the controller 20 detects based on the output of the thermocouple 5 that the temperature T of the thermoelectric element 2 has hardly changed. Then, the AC voltmeter 9 and the DC voltmeter 10 measure the AC component amplitude VAC0 and the DC component VDC of the voltage between both ends of the thermoelectric element 2, respectively. Then, the dimensionless figure of merit ZT is obtained by substituting these values VAC0 and VDC into Equation 1.
The controller 20 can also accurately measure the average temperature T0 of the thermoelectric element 2 with the thermocouple 5 and substitute the average temperature T0 into Equation 1 to obtain the figure of merit Z.
[0017]
As described above, according to the present embodiment, the alternating current IAC and the direct current IDC are simultaneously supplied to the thermoelectric element 2. The figure of merit ZT of the thermoelectric element 2 is detected based on the amplitude VAC0 and the DC voltage VDC of the AC component of the voltage when the temperature T of the thermoelectric element 2 reaches a steady state. As described above, when the alternating current IAC and the direct current IDC are simultaneously supplied to the thermoelectric element 2, the internal current of the thermoelectric element 2 can be increased when the alternating current is supplied and the direct current is supplied as in the conventional technique. The heat distribution does not change.
As described above, Equation 1 is valid only when there is no temperature change between the measurement of the amplitude VAC0 of the AC component of the voltage and the measurement of the DC component VDC. Therefore, as in the present embodiment, precise measurement is possible by simultaneously flowing alternating current IAC and direct current IDC.
[0018]
Further, the alternating current IAC (= b cos ωt) and the direct current IDC (= a) are allowed to flow at the same time, so that the amplitude b of the alternating current IAC and the value a of the direct current IDC can be exactly matched. Since Formula 1 is established only when a = b, it is possible to measure the performance index more accurately by making this coincide strictly.
[0019]
Further, according to the performance index measuring apparatus 1 of the present embodiment, measurement is performed by putting the thermoelectric element 2 in the thermostatic device 6 using the liquid cryogen 15 and evacuating the inside. As a result, the thermoelectric element 2 is not affected by an external temperature change and is in a thermally stable state, so that precise measurement is possible. Furthermore, because of the cryopump effect, there is almost no heat leak, so the constant x is almost 1, and the performance index can be accurately obtained by merely measuring the AC current IAC and the DC current IDC.
[0020]
2 has been described as including the inner chamber 11 and the outer chamber 12, an intermediate chamber may be provided between the inner chamber 11 and the outer chamber 12, and triple or more may be provided. This further stabilizes the temperature of the thermoelectric element and makes the measurement accurate.
[Brief description of the drawings]
FIG. 1 is a block diagram of a performance index measurement apparatus according to an embodiment.
FIG. 2 is a detailed configuration diagram of a figure of merit measurement apparatus. FIG. 3 is a graph showing a current flowing through a thermoelectric element.
FIG. 4 is a block diagram of a figure of merit measuring apparatus according to the prior art.
[Explanation of symbols]
1: performance index measuring device, 2: thermoelectric element, 3: electrode, 4: lead wire 1, 5: thermocouple, 6: thermostatic device, 7: AC current source, 8: DC current source, 9: AC voltmeter, 10: DC voltmeter, 11: inner chamber, 12: outer chamber, 13: inner heater, 14: outer heater, 15: liquid cryogen, 16: vacuum pump, 17: thread, 18: lead wire, 19: thermal anchor, 20 :controller.

Claims (6)

熱電素子(2)の両端部間に電流を流し、その両端部間の電圧を測定して無次元性能指数(ZT)を測定する熱電素子の性能指数測定装置において、
熱電素子(2)に交流電流(IAC)を流す交流電流源(7)と、
熱電素子(2)に交流電流(IAC)と同時に直流電流(IDC)を流す直流電流源(8)と、
熱電素子(2)の両端部にかかる電圧の、交流成分の振幅(VAC0)を測定する交流電圧計(9)と、
熱電素子(2)の両端部にかかる電圧の、直流成分(VDC)を測定する直流電圧計(10)とを備え、
同時に測定した前記電圧の交流成分の振幅(VAC0)及び直流成分(VDC)に基づいて、性能指数(ZT)を求めることを特徴とする熱電素子の性能指数測定装置。In a performance index measuring device for a thermoelectric element that measures a dimensionless figure of merit (ZT) by passing a current between both ends of the thermoelectric element (2) and measuring a voltage between both ends,
An alternating current source (7) for passing an alternating current (IAC) through the thermoelectric element (2);
A direct current source (8) for passing a direct current (IDC) simultaneously with an alternating current (IAC) to the thermoelectric element (2);
An AC voltmeter (9) for measuring the amplitude (VAC0) of the AC component of the voltage applied to both ends of the thermoelectric element (2);
DC voltage voltmeter (10) for measuring the DC component (VDC) of the voltage applied to both ends of the thermoelectric element (2),
A performance index measuring device for a thermoelectric element, wherein the figure of merit (ZT) is obtained based on the amplitude (VAC0) and DC component (VDC) of the AC component of the voltage measured simultaneously. 請求項１記載の熱電素子の性能指数測定装置において、
前記交流電流(IAC)の振幅(b)と、
前記直流電流(IDC)の電流値(a)とを略同一にしたことを特徴とする熱電素子の性能指数測定装置。In the thermoelectric element figure of merit measuring apparatus according to claim 1,
The amplitude (b) of the alternating current (IAC),
A thermoelectric element figure of merit measuring apparatus characterized in that the current value (a) of the direct current (IDC) is substantially the same. 請求項１又は２記載の熱電素子の性能指数測定装置において、
熱電素子(2)を略一定の温度に保って熱の移動を小さくする恒温装置(6)を備えたことを特徴とする熱電素子の性能指数測定装置。In the performance index measuring apparatus for thermoelectric elements according to claim 1 or 2,
A thermoelectric element figure of merit measuring apparatus comprising a thermostatic device (6) that keeps the thermoelectric element (2) at a substantially constant temperature to reduce heat transfer. 請求項１〜３のいずれかに記載の熱電素子の性能指数測定装置において、
熱電素子(2)の温度(T)を測定する温度センサ(5)を備え、
熱電素子(2)内部が熱平衡に達したことを検知し、
前記交流電圧(VAC)、直流電圧(VDC)、及び温度センサ(5)によって測定した熱電素子(2)の平均温度(T0)に基づいて、性能指数(Z)を求めることを特徴とする熱電素子の性能指数測定装置。In the performance index measuring apparatus for thermoelectric elements according to any one of claims 1 to 3,
A temperature sensor (5) for measuring the temperature (T) of the thermoelectric element (2) is provided,
Detecting that the thermoelectric element (2) has reached thermal equilibrium,
A figure of merit (Z) is obtained based on the AC voltage (VAC), the DC voltage (VDC), and the average temperature (T0) of the thermoelectric element (2) measured by the temperature sensor (5). Device figure of merit measurement device. 熱電素子(2)の無次元性能指数(ZT)を測定する性能指数測定方法において
熱電素子(2)の両端部間に、交流及び直流の電流を同時に流し、
熱電素子(2)の両端部間の電圧の、交流成分の振幅(VAC0)及び直流成分(VDC)を測定し、
この交流成分の振幅(VAC0)及び直流成分(VDC)に基づいて、無次元性能指数(ZT)を求めることを特徴とする性能指数測定方法。In the figure of merit measurement method for measuring the dimensionless figure of merit (ZT) of the thermoelectric element (2), alternating current and direct current are passed simultaneously between both ends of the thermoelectric element (2),
Measure the AC component amplitude (VAC0) and DC component (VDC) of the voltage between both ends of the thermoelectric element (2),
A performance index measurement method characterized in that a dimensionless figure of merit (ZT) is obtained based on the amplitude (VAC0) and the DC component (VDC) of the AC component. 熱電素子(2)の性能指数を測定する性能指数測定方法において
熱電素子(2)の両端部間に、交流及び直流の電流を同時に流し、
温度センサ(5)によって、熱電素子(2)の熱分布が熱平衡に達したことを検知し、
熱電素子(2)の両端部間の電圧の、交流成分の振幅(VAC0)、及び直流成分(VDC)を測定し、
熱平衡時の熱電素子(2)の平均温度(T0)を測定し、
この交流成分の振幅(VAC0)、直流成分(VDC)、及び平均温度(T0)に基づいて、性能指数(Z)を求めることを特徴とする性能指数測定方法。In the figure of merit measurement method for measuring the figure of merit of the thermoelectric element (2), an alternating current and a direct current are passed simultaneously between both ends of the thermoelectric element (2),
The temperature sensor (5) detects that the thermal distribution of the thermoelectric element (2) has reached thermal equilibrium,
Measure the AC component amplitude (VAC0) and DC component (VDC) of the voltage between both ends of the thermoelectric element (2),
Measure the average temperature (T0) of the thermoelectric element (2) at the time of thermal equilibrium,
A performance index measurement method characterized in that a figure of merit (Z) is obtained based on the amplitude (VAC0), DC component (VDC), and average temperature (T0) of the AC component.
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