METER MOVEMENTS

Test Instruments & Measuring Devices METER MOVEMENTS METER MOVEMENTS There are three basic meter movements utilized in electrical meters: D’Arsonval, electrodynamometer, and the moving iron vane. Some meter movements can be used for both AC or DC measurements, but in general, each meter movement is best suited for a particular type. EO 1.1 EXPLAIN the following meter movements: a. D’Arsonval b. Electrodynamometer c. Moving iron vane D’Arsonval Movement The most commonly used sensing mechanism used in DC ammeters, voltmeters, and ohm meters is a current-sensing device called a D’Arsonval meter movement (Figure 1). The D’Arsonval movement is a DC moving coil-type movement in which an electromagnetic core is suspended between the poles of a permanent magnet. The current measured is directed Figure 1 D’Arsonval Meter Movement through the coils of the electromagnet so that the magnetic field produced by the current opposes the field of the permanent magnet and causes rotation of the core. The core is restrained by springs so that the needle will deflect or move in proportion to the current intensity. The more current applied to the core, the stronger the opposing field, and the larger the deflection, up to the limit of the current capacity of the coil. When the current is interrupted, the opposing field collapses, and the needle is returned to zero by the restraining springs. The limit of the current that can be applied to this type movement is usually less than one milliampere. Rev. 0 Page 1 ES-14