Voltmeters for Precise Voltage Measurement

Demonstrative Video

Voltmeters

  • Device that can measure the voltage across a circuit element.

  • Since voltage is the difference in potential between two points in a circuit, the voltmeter needs to be connected across the element whose voltage we wish to measure.

  • A voltmeter must also fulfill two requirements:

    1. The voltmeter must be placed in parallel with the element whose voltage it is measuring

    2. The voltmeter should draw no current away from the element whose voltage it is measuring, or else it will not be measuring the true voltage across that element. Thus, an ideal voltmeter has infinite internal resistance.

  • A practical ammeter will contribute some series resistance to the circuit in which it is measuring current.

  • A practical voltmeter will not act as an ideal open circuit but will always draw some current from the measured circuit.

Circuit Connection of Voltmeter

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Classification or Types of Voltmeter

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  1. Analog Voltmeter

    • It includes deflecting type of indicating voltage meters

  2. VTVMs and FET VMs

    • instruments handle both AC/ DC voltages and resistance measurements.

  3. Digital Voltmeter (DVM)

    • DVM displays the voltage using LEDs or LCDs to display the result.

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  • Based on construction

    1. Parmanent Magnet Moving coil (PMMC)

    2. Moving Iron (MI)

    3. Electro Dynamometer type

    4. Rectifier type

    5. Induction type

    6. Electrostatic type

    7. Digital Voltmeter (DVM).

  • Depending on the types of measurement

    • DC Voltmeter.

    • AC Voltmeter.

Applications

  • PMMC \(\rightarrow\) DC measurement

  • MI \(\rightarrow\) both AC and DC

  • Electro-dynamometer \(\rightarrow\) both AC and DC

  • Induction \(\rightarrow\) not used because of high cost, inaccuracy

  • Rectifier, electrostatic, and DVM \(\rightarrow\) both AC and DC