Cambridge Thermionic Voltmeter Type A

Cambridge Scientific Instrument Co.; Cambridge

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  • Year
  • 1928 ?
  • Category
  • Service- or Lab Equipment
  • Radiomuseum.org ID
  • 357589

Click on the schematic thumbnail to request the schematic as a free document.

 Technical Specifications

  • Number of Tubes
  • 1
  • Valves / Tubes
  • Wave bands
  • - without
  • Power type and voltage
  • Dry Batteries / 6 Volt
  • Loudspeaker
  • - - No sound reproduction output.
  • Material
  • Various materials
  • from Radiomuseum.org
  • Model: Cambridge Thermionic Voltmeter Type A - Cambridge Scientific
  • Shape
  • Tablemodel, with any shape - general.
  • Notes

  • The Cambridge Thermionic Voltmeter, also known as the Moullin Voltmeter, was an innovative instrument developed in the early 20th century for measuring alternating current (AC) voltages. Invented by E.B. Moullin of the University of Cambridge in 1922, this device utilized vacuum tube technology to provide accurate voltage measurements with minimal disturbance to the tested circuit.

    Key Features and Functionality

    Operating Principle: The Moullin Voltmeter employed the rectifying properties of a triode vacuum tube to measure AC voltages. 
    It converted the AC input into a change in the direct current (DC) of the plate circuit, which was then used to indicate the voltage on a meter scale.

    High Input Impedance: One of the most significant advantages of this voltmeter was its high input impedance. This characteristic allowed it to measure voltages without drawing considerable power from the circuit under test, making it particularly useful for sensitive measurements.

    Voltage Ranges: Different models of the Moullin Voltmeter were designed to measure various voltage ranges. For example:

    • The Type A model could measure voltages from 0 to 5 volts.
    • The Type B model 0 to 10 volts
    • The Pattern D version had ranges of 0-4 and 0-20 volts.
    • Some models were specifically designed for low voltage measurements, such as 0.5-1.5 volts.

    Versatility: The instrument was capable of measuring AC and DC voltages, making it a versatile tool for electrical measurements.

    Scale Characteristics: The scale of the Moullin Voltmeter was not always linear due to the inherent non-linear nature of vacuum tubes. However, some models featured scales that were linear within specific voltage ranges.

    Construction: The voltmeter was typically housed in a polished wooden case with an ebonite front panel, reflecting the craftsmanship of scientific instruments of that era.

    The Cambridge Thermionic Voltmeter represented a significant advancement in electrical measurement technology, offering a method to measure AC voltages with high sensitivity and minimal circuit interference. Its development paved the way for more sophisticated electronic measurement instruments in the following decades.

  • Mentioned in
  • Elektrische Gleichrichter und Ventile, Prof. Dr.-Ing. A.Güntherschulze of the Physikalisch-Technisch
  • Literature/Schematics (1)
  • -- Other type before this -same/similar characteristics - see exchange. (University of Queensland AU 43 Thermionic Voltmeter)
  • Author
  • Model page created by Wolfgang Müllner. See "Data change" for further contributors.

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