【発明の詳細な説明】
（産業上の利用分野）
本発明は重量を機械歪に変換する起歪体の歪量を電気信
号に変換して出力するようにした計量装盲用の温度補償
回路に開する．
（従来技術）
電子秤等の起歪体の歪ｊｌを電気信号に変換する回路は
、第３図に示したように信号取出端子を挟んで対向する
各２辺に起歪体に貼着ざれた歪ゲージＡ，Ａ’ Ｂ
，Ｂ’ ＠接続してなるブリッジ回路Ｄと、このブリッ
ジ回路Ｄの信号出力端子に非反転入力端子をそれぞれ接
続し、また反転入力端子に起歪体に密着させた感温抵抗
素子巳を接続してなる演算増幅器Ｆ，Ｇと、これら演算
増幅器Ｆ，Ｇの出力を受ける差動増幅回路Ｈからなり、
起歪体を構成しでいる金属、通常アルミニウム合金のヤ
ング率の温度特性や、歪ゲージの抵抗の温度特性による
重量信号の変動を感温抵抗素子Ｅを備えた増幅回路の増
幅率の変化により補正することが行なわれている．
（解決しようとする課題）
このような回路によれば、補償温度設定点を挟む比較的
狭い温度（こ対じでは、高い精度で重量信号を補正でき
るものの、ブリッジ回路からの出力の温度特性と、感温
抵坑素子Ｅを含む増幅回路の出力の温度特性が正の２次
特性を有するため、第４図に示したように補償温度設定
点Ｔ。かう隔たるにつれで誤差ΔＬが急激（こ大きくな
るという問題を依然としで抱えている．
このような問題を解消するため、ブリッジ回路に直列に
感温抵抗素子を接続してブリ・ンジ出力の温度特性を改
善することも考えられるが、このような温度補償は汎用
性を欠くためにコストの上昇を招くばかりでなく、起歪
体や歪ゲージの特牲に合う感温抵抗を多数用意する必要
があるという新たな問題を招く，
本発明はこのような問題に鑑みでなされたもので、その
目的とするところは、コストの増大を招くことなく広い
温度節囲に亘って高い精度で温度補償を行なうことがで
きるロードセル用温度補償回″ｉｌ！１を提供すること
にある．
（課題を解決するための手段）
それぞれの非反転入力端子が起歪体の表面に設けられた
複数の歪ゲージを含むブリッジ回路の各信号出力端に、
またそれぞれの反転入力端子を正の２次温度係数を有し
ない金居と、正の２次温度係数を有する金属と８１１２
続してなる感温抵抗素子と、１次温度係数をマッチシグ
させるための精密抵抗により接続しＰ第１、第２の演算
増幅器を備えた．
（作用）
ブリッジ出力は、正の２次温度係数をもった特性である
のに対しで、増幅回路自体は負の２次温度係数をもった
温度特性に調整ざれるので、増幅回路の出力の温度係数
は、正／負の２次係数を打消すように作用して過補償分
を相殺し、可及的に広い温度範囲にわたっで平坦化する
．
（実施例）
そこで、以下に本発明の詳細を図示した実施例に基づい
て説明丁る．
第１図は本発明の一実施例を示すものであって、図中符
号１は、起歪体に貼若ざれた歪ゲージ３、３′ ４、
４゛を４辺に有するブリッジ回路である．６、７は、そ
れぞれ第１、第２の演算増幅器で、それぞれ非反転入力
端がブリッジ回路１の信号出力端１こ接続され、また反
転入力端子が精ヱ抵抗８、９を介して出力端子に接続さ
れるとともに、各反転入力端子間を後述する感温抵抗素
子１０と精密抵抗１２１こより接続されでいる，１０は
、前述の感温抵抗素子で、２次係数成分を有しない銅、
または負の２次係数を有する白金等の第１の感温抵抗素
子１０ａと、正の２次係数を有するニッケル等のＭ２の
感温抵抗素子１０ｂとを直列、もしくは並列に接続して
構成ざれている．１２は、１次温度係数をマッチングさ
せるための精密抵抗１２で、この実施例（こおいでは感
温抵抗素子１０に直列接続されている．なお、図中符号
１４は、演算増幅器６、７から出力を受けるとともに、
これと協働して高入力インピーダンス差動増幅回路を構
成する差動増幅回路を示す．ところで銅からなる第１の
感温抵抗素子１０ａの温度一抵抗特性は、第２図（Ｉ）
に示したように温度に対して正の１次温度特性を示し、
またニッケルからなる第２の感温抵抗素子１０ｂの温度
一抵抗特性は同図（ＩＩ）に示したように正の１次、正
の２次の温度一抵抗特性を示す．この実施例においで、
予め起歪体を含むブリッジ回路１の温度変化に対する出
力信号の変化を測定してブリッジ出力の温度一出力特性
を調査する．この温度一出力特性を１＋α，Ｐ２５Δ丁
（ただしα，Ｐ２，は温度係数、Δ丁は補償温度設定点
からの温度差を表わす）なる式で近似して係数α，，２
５を求める．
このようにしてブリッジ出力の温度係数α，，２５が定
まった段階で、演算増幅器６、７、及び差動増幅回路１
４かうなる高入力差動増幅回路の出力の温度係数を求め
、これからの出力がほぼ平坦化するように銅、ニッケル
等を組合せた感温抵抗素子１０、及び精密抵抗１２のそ
れぞれの抵抗値の合せ込みを行なう．
基準温度を２５℃とし、（２５＋Ｔ）’Ｃにおけるブリ
ッジ回路の定格出力Ｉｆ （Ｔ）とすると、ｆｓｐ（Ｔ
） Ａｓｐ２ｓ（１＋αｓｐｔ＝ｔ’Ｔ ）ただし、
α８Ｐ２６：２５℃におけるブリッジ出力の温度係数
■ ＝２５℃からの温度差
α＋ｓｐ：２５℃におけるブリッジ出力の温度係数定数
項
α２，Ｐ．温度変化したときのブしｉツジ出力の温度係
数の温度依存項
αｓｐ２５ｘαＩｓＰ＋α２ＳＰ Ｔ
により表すことができる．
一方、（２５＋Ｔ）”Ｃにおける高入力差動増幅回路の
増幅率をｆ．（Ｔ）とすると、
ブリッジの出力と高入力差動増幅回路とを組合せたとき
の全体の出力８ ｆ ．（Ｔ）とすると、ｆｔ（Ｔ）・
ｆｓｐ（Ｔ）ｆ．（Ｔ）
ただし、Ｒ ｓｏ２５： ２ ５ ”Ｃにおける入力抵
抗の感温抵抗値
日，，二入力抵抗の精と抵抗イａ
Ｂｆ ：帰還抵抗値
αＳ２５：２５℃における増幅率の温度係数α１
２５゜Ｃにおける増幅率温度係数定数項α２ ・温度
変化したときの増幅率温度係数の温度依存項
α２５＝α１＋α２丁
としで表すことができる．
争α２α１Ｓｐ）Ｔ令α２ＳＰα７２）Ｔ２１ここで、
上記出力ｆ，（Ｔ）の温度変化を抑えるためには、３次
以上の項を無視すると、１次、２次の項かゼロとなるよ
うにすればよいから、となる．この粂件を溝足するよう
に各抵抗値Ｒｆ１Ｒ ５２５、ＲＳＩＰ８設定すればよ
い．ただし、α１，Ｐ１α２８Ｐは実験により求めたブ
リッジ出力の温度特性により一義的に定まり、またα，
、α２は使用する感温抵抗素子の温度係数に依存し、ざ
らに増幅率（ １ ＋ ２Ｒ ｆ／ （Ｒ ｓｏｔｓ÷
Ｒｓ＋）をいくらにするかによって抵抗値Ｐｆｚ日，。Detailed Description of the Invention (Industrial Field of Application) The present invention provides a temperature compensation circuit for a weighing device that converts the amount of strain in a strain-generating body that converts weight into mechanical strain into an electrical signal and outputs the electrical signal. Open to. (Prior art) A circuit that converts the strain jl of a strain-generating body such as an electronic scale into an electrical signal is attached to the strain-generating body on each of two opposing sides with a signal output terminal in between, as shown in Fig. 3. Strain gauges A, A'B
, B'@ are connected, and a non-inverting input terminal is connected to the signal output terminal of this bridge circuit D, and a temperature-sensitive resistive element 3, which is in close contact with the strain-generating body, is connected to the inverting input terminal. It consists of operational amplifiers F and G, and a differential amplifier circuit H that receives the outputs of these operational amplifiers F and G,
Fluctuations in the weight signal due to the temperature characteristics of the Young's modulus of the metal that constitutes the strain body, usually an aluminum alloy, and the temperature characteristics of the resistance of the strain gauge can be controlled by changes in the amplification factor of the amplifier circuit equipped with the temperature-sensitive resistance element E. Corrections are being made. (Problem to be Solved) According to such a circuit, the temperature characteristics of the output from the bridge circuit are , the temperature characteristic of the output of the amplifier circuit including the temperature-sensitive resistance element E has a positive quadratic characteristic, so as shown in FIG. In order to solve this problem, it is possible to improve the temperature characteristics of the bridge output by connecting a temperature-sensitive resistor element in series with the bridge circuit. This type of temperature compensation not only increases costs due to its lack of versatility, but also introduces a new problem in that it is necessary to prepare a large number of temperature-sensitive resistors that match the characteristics of the flexure element and strain gauge. The present invention was made in view of these problems, and its purpose is to provide temperature compensation for load cells that can perform temperature compensation with high accuracy over a wide temperature range without increasing costs. (Means for solving the problem) Each signal output terminal of a bridge circuit including a plurality of strain gauges each having a non-inverting input terminal provided on the surface of a strain-generating body. To,
In addition, each inverting input terminal is connected to a metal that does not have a positive second-order temperature coefficient, and a metal that has a positive second-order temperature coefficient.
The first and second operational amplifiers were connected to a temperature-sensitive resistance element connected to the P-type through a precision resistor for matching the first-order temperature coefficient. (Function) The bridge output has a characteristic with a positive second-order temperature coefficient, whereas the amplifier circuit itself is adjusted to have a temperature characteristic with a negative second-order temperature coefficient. The temperature coefficient acts to cancel out the positive/negative quadratic coefficient, canceling out the overcompensation, and flattening the temperature over the widest possible temperature range. (Example) Therefore, the details of the present invention will be explained below based on an illustrated example. FIG. 1 shows an embodiment of the present invention, and reference numeral 1 in the figure indicates strain gauges 3, 3' 4,
It is a bridge circuit with 4゛ on the four sides. 6 and 7 are first and second operational amplifiers, respectively, whose non-inverting input terminals are connected to the signal output terminal of the bridge circuit 1, and whose inverting input terminals are connected to the output terminals via precision resistors 8 and 9. At the same time, the inverting input terminals are connected through a temperature-sensitive resistance element 10 and a precision resistor 121, which will be described later. 10 is the above-mentioned temperature-sensitive resistance element made of copper, which does not have a quadratic coefficient component,
Alternatively, the first temperature-sensitive resistance element 10a made of platinum or the like having a negative quadratic coefficient and the M2 temperature-sensor resistance element 10b made of nickel or the like having a positive quadratic coefficient are connected in series or in parallel. ing. Reference numeral 12 denotes a precision resistor 12 for matching the primary temperature coefficient, which is connected in series to the temperature-sensitive resistor element 10 in this embodiment. Along with receiving the output,
A differential amplifier circuit that works together with this to form a high input impedance differential amplifier circuit is shown. By the way, the temperature-resistance characteristics of the first temperature-sensitive resistance element 10a made of copper are shown in FIG. 2(I).
As shown in , it shows a positive first-order temperature characteristic with respect to temperature,
Further, the temperature-resistance characteristics of the second temperature-sensitive resistance element 10b made of nickel exhibit positive first-order and positive second-order temperature-resistance characteristics, as shown in FIG. In this example,
The temperature-output characteristics of the bridge output are investigated by measuring in advance the change in the output signal with respect to the temperature change of the bridge circuit 1 including the flexure element. This temperature-output characteristic is approximated by the formula 1+α,P25Δt (where α, P2, are temperature coefficients, and Δt represents the temperature difference from the compensation temperature set point), and the coefficient α,,2
Find 5. When the temperature coefficient α, 25 of the bridge output is determined in this way, the operational amplifiers 6 and 7 and the differential amplifier circuit 1
Find the temperature coefficient of the output of the four high-input differential amplifier circuits, and calculate the respective resistance values of the temperature-sensitive resistance element 10, which is a combination of copper, nickel, etc., and the precision resistor 12, so that the output from now on will be almost flat. Perform fitting. If the reference temperature is 25℃ and the rated output If (T) of the bridge circuit at (25+T)'C, then fsp(T
) Asp2s(1+αspt=t'T) However,
α8P26: Temperature coefficient of bridge output at 25°C ■ = Temperature difference from 25°C α+sp: Temperature coefficient constant term α2, P. It can be expressed by the temperature dependent term αsp25xαIsP+α2SP T of the temperature coefficient of the brush output when the temperature changes. On the other hand, if the amplification factor of the high-input differential amplifier circuit at (25+T)''C is f.(T), then the total output when the bridge output and the high-input differential amplifier circuit are combined is 8 f.(T ), then ft(T)・
fsp(T)f. (T) However, Rso25: Temperature-sensitive resistance value of input resistance at 2 5 ''C,, Estimate of two input resistances and resistance a Bf: Feedback resistance value αS25: Temperature coefficient α1 of amplification factor at 25°C
Amplification factor temperature coefficient constant term α2 at 25°C ・Temperature dependence term of amplification factor temperature coefficient when temperature changes α25 = α1 + α2 It can be expressed as follows. α2α1Sp)T orderα2SPα72)T21Here,
In order to suppress the temperature change in the above output f, (T), if we ignore the third-order and higher-order terms, it is sufficient to make the first-order and second-order terms zero. Each resistance value Rf1R should be set to 525 and RSIP8 to satisfy this requirement. However, α1, P1α28P are uniquely determined by the temperature characteristics of the bridge output obtained through experiments, and α,
, α2 depends on the temperature coefficient of the temperature-sensitive resistance element used, and is roughly calculated by the amplification factor (1 + 2R f/ (R sots ÷
The resistance value Pfz depends on how much Rs+) is set.
２６、日８１の抵抗値の比が決るので、これらから上記
２式を満足する抵抗素子１ｏと精密抵抗１２の各々の抵
抗値か定まる．
これにより、ブリッジ回路１がら出力した信号の正の２
次温度変化分は、高入力差動増幅回路自体の負の２次温
度変化分により相殺されるから、温度補償設定点Ｔ。を
中心に広い温度範囲に亘る温度変化に閉わつなく、重ｊ
ｉだけに比例した信号を出力することになる．
なお、この実施例においては差動増幅１４との組合せに
よる高人力インピーダンス型増幅器に適用しているが、
第３図に示したように高入力インピーダンス反転回路に
適用しても同様の作用効果を奏することは明らかである
．
（発明の効果）
以上、説明したように本発明においては、それぞれの非
反転入力端子か起歪体の表面に設けられた複数の歪ゲー
ジを含むブリッジ回路の各信号出力端に、またそれぞれ
の反転入力端子を正の２次温度係数を有しない金屈と、
正の２次温度係数を有する金属とを接続しでなる感温抵
抗素子と、１次温度係数をマッチングさせるための精記
抵抗により′＋ｉｔ続した第１、第２の演算増幅器を備
えたので、銅やニッケルという安価な第１、及び第２の
抵抗素子の比率を調整することによりアルミニウム合金
製起歪体と、これに設けた銅一ニッケル合金、またはニ
ッケルークロム合金製の歪ゲージを有するブリッジ出力
の温度特性に実用上充分に一敗した温度一抵抗特性に合
せ込むことが可籠となって、コストの増大を招くことな
く広い温度範囲で高い計量精度を得ることがＣきる。Since the ratio of the resistance values of 26 and 81 is determined, the resistance values of each of the resistance element 1o and the precision resistor 12 that satisfy the above two equations are determined from these. As a result, the positive 2 of the signal output from the bridge circuit 1
Since the second-order temperature change is offset by the negative second-order temperature change of the high-input differential amplifier circuit itself, the temperature compensation set point T. It does not close to temperature changes over a wide temperature range mainly in
It will output a signal proportional only to i. Although this embodiment is applied to a high-power impedance amplifier in combination with the differential amplifier 14,
It is clear that similar effects can be achieved even when applied to a high input impedance inversion circuit as shown in Figure 3. (Effects of the Invention) As explained above, in the present invention, each non-inverting input terminal is connected to each signal output terminal of a bridge circuit including a plurality of strain gauges provided on the surface of a strain body, and each Connect the inverting input terminal to a metal connector that does not have a positive quadratic temperature coefficient,
It is equipped with a temperature-sensitive resistance element connected to a metal having a positive second-order temperature coefficient, and first and second operational amplifiers connected by a precision resistor for matching the first-order temperature coefficient. By adjusting the ratio of inexpensive first and second resistive elements such as copper and nickel, an aluminum alloy strain body and a copper-nickel alloy or nickel-chromium alloy strain gauge attached thereto can be used. It is possible to match the temperature-resistance characteristics of the bridge output with the temperature-resistance characteristics that are sufficiently inferior in practical use, and it is possible to obtain high measurement accuracy over a wide temperature range without increasing costs.
【図面の簡単な説明】[Brief explanation of drawings]
第１図は本発明の一実施例を示す装３の構成図、第２図
は同上装コに使用する温度抵抗素子の一例を示す線図、
第３図は本発明の他の実施例を示す構成図、及び第４、
５図はそれぞれ従来の温度補償回路の一例を示す構成図
と、その温度補償特性を示す線図である．
１・・・・ブリ・ンジ回路
３、３′ ４、４′・・・・歪ゲージ
６、７・・・・演算増幅器
１０・・・感温抵抗素子
１０ａ・・・・銅抵抗素子
１０ｂ・・・・ニッケル抵抗素子
］２・・・精密抵抗素子
出願人 株式会社石田衡器製作所
代理人 弁理士 木 村 勝 彦
同 西川慶治
第１図
第２図
壜屋
第４図
第５図FIG. 1 is a configuration diagram of a housing 3 showing an embodiment of the present invention, and FIG. 2 is a diagram showing an example of a temperature resistance element used in the same upper housing.
FIG. 3 is a configuration diagram showing another embodiment of the present invention, and FIG.
Figure 5 is a configuration diagram showing an example of a conventional temperature compensation circuit, and a diagram showing its temperature compensation characteristics. 1... Bridge circuit 3, 3' 4, 4'... Strain gauge 6, 7... Operational amplifier 10... Temperature sensitive resistance element 10a... Copper resistance element 10b. ...Nickel resistance element] 2...Precision resistance element Applicant Ishida Koki Seisakusho Co., Ltd. Agent Patent attorney Katsuhiko Kimura Keiji Nishikawa Figure 1 Figure 2 Tsuya Figure 4 Figure 5