Potentiometer - Electrical

Japanese: 電位差計 - でんいさけい

This device uses the so-called null method to measure voltage or electromotive force by balancing a known standard voltage with an unknown voltage or electromotive force. Its distinctive feature is that it can measure without drawing current from the voltage or electromotive force to be measured, and the balance is detected by a highly sensitive galvanometer.

[Toshiharu Takao]

DC Potentiometer

This is measured by comparing the potential difference calibrated using the electromotive force of a standard battery with the voltage to be measured. Currently, DC power sources with sufficient accuracy are used instead of standard batteries. The accuracy of the measurement is related to the accuracy of the standard voltage and the sensitivity of the galvanometer, and measurement values can be obtained to six digits. It is widely used as a standard measuring instrument for "calibrating" or calibrating voltmeters.

[Toshiharu Takao]

principle

A current (potentiometer current i ) is passed through a finely graduated scaled slide resistance wire AB. Next, a galvanometer G is connected in series to the scale at the same value as the value of the electromotive force E _s of the standard battery at room temperature (point C). At first, the galvanometer produces a so-called "fluctuation" because there is a difference between the voltage of the resistance wire and the electromotive force of the standard battery. However, if the fluctuation is reduced to zero by adjusting the potentiometer current resistance R, the scale on the resistance wire will become the correct voltage scale. Next, switch K to the E _x side, swap the standard battery with the unknown voltage E _x , and move the connection point C on the slide resistance wire so that the galvanometer fluctuation is again zero. The scale at which the fluctuation becomes zero is the value of the unknown voltage. It is important that the electromotive force of the battery E _b remains constant during measurement. The maximum measurement voltage is usually 2 volts or less, and for values higher than this, a voltage divider box is used. Currently, methods that do not include a slip resistor or _battery Eb circuit, but rather measure the unknown voltage E _x directly by balancing it with the electromotive _{force Es} of a variable standard voltage generator via a galvanometer, or by measuring the unknown voltage directly with a high-precision digital multimeter, are used.

[Toshiharu Takao]

AC Potentiometer

In the case of AC, the amplitude, frequency, phase, and waveform of the two voltages, the standard and unknown, must match in order to achieve perfect balance. For this reason, the sensitivity is lower than in the case of DC, and the structure and operation are complicated, so it is rarely used today.

[Toshiharu Takao]

[Reference item] | Galvanometer | Zero position method

Principle of Potentiometer
©Shogakukan ">

Principle of Potentiometer

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

既知の標準電圧と未知の電圧や起電力を平衡させて電圧や起電力の値を測定する、いわゆる零位法を利用した装置。測ろうとする電圧や起電力から電流をとらない状態で測定できるのが特長で、平衡は高感度の検流計で検出する。

［高尾利治］

直流電位差計

標準電池の起電力で校正した電位差と、測ろうとする測定電圧とを比較して測定するもの。現在は、標準電池のかわりに、十分な精確度を有する直流電源が用いられている。測定の精度は標準電圧の精確度と検流計の感度とに関係し、測定値は6桁(けた)まで得られる。電圧計の「目盛り定め」あるいは校正の標準測定器として広く用いられている。

［高尾利治］

原理

細かい目盛りをつけたすべり抵抗線ABに電流（電位差計電流i）を流す。次に、そのときの室温における標準電池の起電力E_sの値と等しい目盛りのところへ、検流計Gを直列にして接続する（C点）。初めは抵抗線の電圧と標準電池の起電力とに差があるので、検流計がいわゆる「振れ」を生ずるが、電位差計電流抵抗Rを調整して、振れをゼロにすると、抵抗線上の目盛りが電圧の正しい目盛りになる。次にKをE_x側に切り換え、標準電池と未知電圧E_xを入れ換え、ふたたび検流計の振れがゼロになるように、今度はすべり抵抗線上の接続点C点を移動させる。振れがゼロになった点の目盛りが未知電圧の値である。電池E_bは、測定に際し起電力の値が一定不変であることがたいせつである。最大測定電圧は普通2ボルト以下で、それ以上の値の場合は分圧箱を用いる。現在は、すべり線抵抗器や電池E_bの回路を設けず、直接未知電圧E_xと可変標準電圧発生器の起電力E_sとを、検流計を介して平衡させて測定する方法や、高精度のデジタルマルチメーターで直接、未知電圧を測定する方法などが用いられている。