Electrical Interview:PMMC INSTRUMENT

      The equation for the developed torque of the PMMC can be obtained from basic law of electromagnetic torque. The deflecting torque is given by
                                 
                                                       Td = NBAI 
                                                       Td = KI
                                                                          Where G = NBA= constant.

    From the above conclusion the the developed torque(Td) is proportional to electrical current flowing in the coil(I).If this type of meter is connected in DC supply the produced torque is unidirectional and shows some  reading.Now PMMC connected in AC supply the PMMC for first positive half cycle produce positive torque for next negative half cycle produce negative torque,due to this problem the meter will show zero reading therefore the PMMC do not operate in AC supply practically.