Voltmeter - Voltage meter

Japanese: 電圧計 - でんあつけい

An instrument used to measure the voltage in an electric circuit. Also called a voltmeter. There are various types of voltmeters depending on the magnitude of the voltage to be measured, whether it is direct or alternating current, high or low frequency, and the level of measurement accuracy required. Generally, digital voltmeters that display the measurement result in numbers and indicating voltmeters that show the result with a scale and a needle are used. Indicating voltmeters can be classified based on their operating principle into moving coil type, moving iron type, electrodynamic type, electrostatic type, and thermocouple type. The main types are shown below.

[Toshiharu Takao]

Digital voltmeter

A voltmeter that uses electronic digital technology to convert the measured voltage into a digital signal and display it as a number. It is currently in wide use. It is more accurate than a pointer-type voltmeter, and since the measurement result is displayed as a number, there is no reading error. Another feature is that, if necessary, the measurement result can be output directly as a digital signal to an external device and immediately processed by a computer.

[Toshiharu Takao]

Moving coil voltmeter

A voltmeter exclusively for direct current. It consists of a strong permanent magnet that creates a uniform radial magnetic field, and a moving coil placed within that field. A high resistance is connected in series to the moving coil, and a current proportional to the voltage being measured flows through it, which generates a driving torque proportional to the current. When the driving torque rotates the coil, a control spring attached to the shaft is activated, generating a control torque in the opposite direction to the rotation. The control torque increases as the coil rotates, so the pointer attached to the coil stops at the position where the two torques are balanced. In practice, various types of braking are applied to quickly stop the pointer and make it easier to read. This type of voltmeter is sensitive and not easily affected by changes in ambient conditions, so it is also used for alternating current as a rectifier-type instrument or a thermocouple-type instrument combined with a semiconductor rectifier or thermocouple. It is also widely used in combination with various sensors as an indicator for temperature, pressure, speed, etc.

[Toshiharu Takao]

Moving iron type voltmeter

A voltmeter exclusively for AC. It is used for AC from commercial frequencies up to about 400 Hz. It uses the repulsive or attractive force generated between two pieces of iron placed in a magnetic field proportional to the voltage to be measured as the driving torque.

[Toshiharu Takao]

Electrostatic voltmeter

A voltmeter that can be used for both AC and DC. It uses the attractive force between two oppositely charged electrodes as the driving torque. It has the advantage that it requires almost no current from the voltage source to be measured. It is used to measure high voltages of several kilovolts or more.

[Toshiharu Takao]

[Reference] | Digital Instruments | Voltage

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

電気回路の電圧を測る計器。ボルトメーターvoltmeterともいう。測ろうとする電圧の大きさの程度、直流か交流か、高周波か低周波か、測定の正確さをどの程度要求するかなどによって各種の電圧計がある。一般には測定結果を数字で表示するデジタル電圧計と、目盛りと指針とで示す指示電圧計とが使われている。指示電圧計を動作原理から分類すると、可動コイル型、可動鉄片型、電流力計型、静電型、熱電対(ねつでんつい)型などがある。おもなものを以下に示す。

［高尾利治］

デジタル電圧計

電子技術を応用したデジタル技術により、測定電圧をデジタル信号に変換し、これを数字で示す電圧計。現在広く使われている。指針型電圧計に比べて精度がよく、測定結果が数字で表示されるため読み取りの誤差がない。また、必要な場合は測定結果をデジタル信号としてそのまま外部に取り出し、ただちに計算機処理ができるなどの特長がある。

［高尾利治］

可動コイル型電圧計

直流専用の電圧計。放射状の平等磁界をつくる強力な永久磁石と、その磁界内に置かれた可動コイルからできている。可動コイルには高抵抗が直列に接続されており、測る電圧に比例した電流が流れ、コイルはその電流に比例した駆動トルクを生ずる。さらに駆動トルクによってコイルが回転すると、軸に取り付けられた制御ばねが働き、回転と逆向きの制御トルクが生ずる。制御トルクはコイルの回転とともに増すので、両トルクのつり合った位置で、コイルに取り付けられた指針は静止する。実用的には指針を速やかに静止させ、読み取りを容易にするため各種の制動が加えられる。この形式の電圧計は感度がよいうえに周囲条件の変化の影響も受けにくく、安定しているので、半導体整流器や熱電対などと組み合わせた整流器型計器や熱電対型計器として交流にも使用されている。また、各種のセンサーと併用して温度、圧力、速度などの指示計としても広く用いられている。

［高尾利治］