Astatic Electrical Measuring Instrument

an instrument in which the measuring mechanism is constructed with an astatic arrangement, reducing the influence of external magnetic fields to acceptable limits. Two similar moving parts (such as electromagnetic windings) are mounted similarly together on a common axis; when magnetic fields act on them, torques are developed in mutually opposing directions that balance the system. Among such instruments are ammeters (milliammeters) of the AST type, voltmeters of the AMV type, and wattmeters of the ASD type produced by industry in the USSR; these instruments are in the 0.5 accuracy class. They are used for precision laboratory measurements in DC and AC circuits (at a frequency of 50 hertz) and for checking similar instruments of lower classes.