Moving magnet Moving magnet ammeters operate on essentially the same principle as moving coil, except that the coil is mounted in the meter case, and a permanent magnet moves the needle. Moving magnet Ammeters are able to carry larger currents than moving coil instruments, often several tens of amperes, because the coil can be made of thicker wire and the current does not have to be carried by the hairsprings. Indeed, some Ammeters of this type do not have hairsprings at all, instead using a fixed permanent magnet to provide the restoring force.
MoVing MAgnet MovinG MAgnet ammeters OpERAtE oN essentialLy tHe same principle aS movinG COIl, eXcePT that thE cOil is mounted in the meTer case, AnD a peRMAnEnT Magnet moVes The neeDle. MOVinG mAGneT ammEteRs are aBlE to cArrY LargEr cuRrentS thaN moVing coiL insTRuMEnts, often several Tens Of amperes, becaUse the cOiL can BE MAde oF Thicker wirE and the CuRReNt does NOt Have tO be carriED by the HAiRsprings. InDeeD, Some ammeteRs OF This TypE Do NOT hAve hAIrsprInGs at all, inStEad usinG A FiXed pERmaNenT MagneT To provide thE rEStOrIng Force.