Standard battery - hyojundenchi (English spelling) standard cell

Japanese: 標準電池 - ひょうじゅんでんち（英語表記）standard cell

A primary cell that exhibits a highly accurate electromotive force and is used to calibrate the voltage of electronic devices and experimental equipment. The cadmium standard cell, which exhibits a constant electromotive force at a constant temperature, is commonly used. It is also called the Weston standard cell because it was invented by Weston. It uses cadmium-10% amalgam Cd (10% Hg) for the negative electrode, mercury Hg and mercury(I) sulfate Hg ₂ SO ₄ for the positive electrode, and a saturated aqueous solution of cadmium sulfate 8/3 hydrate CdSO ₄ 8/3 H ₂ O for the electrolyte, and can be shown as follows:

Cd(10%Hg)｜CdSO ₄・8/3H ₂ O
｜CdSO ₄ (H ₂ O)｜Hg ₂ SO ₄ ｜Hg
The electromotive force is E ₂₀ = 1.01830±1×10 ^-5 volts at 20°C. The difference in electromotive force due to temperature change is extremely small, but internationally, between 0 and 40°C, it is corrected using the following Borff's formula.

E _t = E ₂₀ -4.06×10 ^-5 ( t -20)
-9.5× ^10-7 ( t -20) ²
+1× ^10-8 ( t -20) ³
Here, Et is _the electromotive force at temperature t °C.

If high-purity chemicals are used and the device is assembled carefully and accurately, it will have good long-term stability. If the device is handled with care, such as not passing current during calibration, avoiding direct sunlight, and not subjecting it to vibration or tipping, the deterioration over time can be kept to less than a few microvolts (μV) per year.

In addition, Clark cells, which used zinc sulfate _ZnSO4 instead of the cadmium sulfate of the cadmium standard battery, were once used as standard batteries, but they are rarely used today because of their relatively large temperature coefficient.

Since the Josephson voltage standard has been established since the 1970s, the standard battery serves as a secondary standard.

[Mitsuru Asano]

"Battery Handbook" edited by the Battery Handbook Editorial Committee (2001, Maruzen)

[References] | Primary batteries | Weston | Josephson

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

電子機器や実験装置などの電圧の校正用に用いられる精度の高い起電力を示す一次電池。一定の温度で一定の値の起電力を示すカドミウム標準電池が一般に用いられている。ウェストンによって発明されたためウェストン標準電池ともよばれている。負極にカドミウム‐10％アマルガムCd(10％Hg)を、正極に水銀Hgと硫酸水銀(Ⅰ)Hg₂SO₄を、そして電解液には硫酸カドミウム・8/3水和物CdSO₄・8/3H₂Oの飽和水溶液を用いたもので、以下のように示すことができる。

　　Cd(10％Hg)｜CdSO₄・8/3H₂O
　　　｜CdSO₄(H₂O)｜Hg₂SO₄｜Hg
　起電力は20℃でE₂₀＝1.01830±1×10^-5ボルトである。温度変化による起電力差はきわめて小さいが、国際的には0～40℃の間では下記に示すボルフの式で補正することになっている。

　　E_t＝E₂₀－4.06×10^-5(t－20)
　　　　－9.5×10^-7(t－20)²
　　　　＋1×10^-8(t－20)³
ここでE_tは温度t℃における起電力である。