This is an early multi-meter: it can measure volts or amps.Įdward Weston revolutionized the field of instrumentation when he developed the first portable electric meters and a reliable PMMC (permanent magnet moving coil instrument). In the voltmeter we need to be able to measure the small sample of current.Ībility to measure milli and microamps leads to the voltmeter: Click on the image to magnify. The Ammeter was developed first because it was easier to measure higher current. More sensitive ammeters led to the voltmeter. Voltmeters were really measuring the current through a resistor. The voltmeter measures current (marked by the “A” for ammeter) but has a resistor in parallel. The ammeter on the other hand is positioned in series with the circuit. The voltmeter works by measuring the potential difference between two points. The way the voltmeter is positioned in the circuit is different from the ammeter. To the right you will see a simple schematic of the voltmeter reading the DC voltage of a circuit that consists of a battery and lightbulb.
To see the science and engineering of the voltmeter we recommend you watch our short video below, if you saw this video at the start of Unit 1 already you can move on. In this page we talk about PMMC or moving coil galvanometer type voltmeters which were the first voltmeters and dominated the industry for over 100 years until they were replaced by wide use of digital multimeters (DMMs). Voltmeters can use magnetic fields, electrostatic fields, and plasma phenomena to measure voltage. They are used in everything from x-ray machines to radio transmission, computers to power utility and atmospheric science measurement to the Hubble Telescope.
The voltmeter is a key instrument in our world of electrical technology.
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