The amount by which the electromagnetic coil moves, called “deflection”, is proportional to the strength of current flowing through the coil needed to produce the magnetic field required to deflect the needle. Permanent Magnet Moving Coil Meter Construction Since the galvanometer responds to an internal flow of current, if we know the internal resistance of the coil (wound from copper wire), we can simply use Ohm’s law to determine the corresponding potential difference that is being measured. When connected to a circuit, an electrical current flows through the coil which inturn generates its own magnetic field (electromagnetism) that reacts against the magnetic field created by the surrounding permanent magnet thus causing the coil to move. The moving-coil movement uses a fixed permanent magnet and a coil of very thin wire which is allowed to move (hence the name “moving-coil”) within the magnetic field of the magnet. This type of analogue meter movement is basically a current measuring device (termed galvanometer) which can be configured to operate as either a Voltmeter or as an Ammeter, the principal difference is the way in which they are connected in a circuit. The most basic type of DC analogue voltmeter is the “permanent-magnetic moving-coil” (PMMC) meter, also known as a D’Arsonval movement. Thus voltage, V is always measured across or in parallel with a circuit component. That is there is a difference in potential of 12.6 volts between the batteries positive and negative terminals. Voltmeters can be used to measure the voltage drop across a single component or supply, or they can be used to measure the sum of voltage drops across two or more points or components within a circuit.įor example, if we connect a voltmeter across the terminals of a fully-charged automobile battery, it will indicate 12.6 volts. To measure a voltage (potential difference), a voltmeter must be connected in parallel with the component whose voltage you wish to measure. Voltmeters can also be used to measure DC voltage as well as sinusoidal AC voltages but the introduction of a voltmeter as a measuring instrument into a circuit can interfere with its steady state conditions.Īs its names implies, a “Voltmeter” is an instrument used for measuring voltage (V), that is the potential difference present between any two points within a circuit. Voltmeters used for the measurement of voltage come in many shapes and sizes, either analogue or digital, or as part of a digital multimeter more commonly used today. When analysing the operation of electrical and electronic circuits, or trying to understand why a circuit does not work as expected, eventually you will need to use a Voltmeter to measure the various voltage levels.

How to use a voltage meter ideal