The DD28 series single phase meter is a kind of induction meter to measure the single phase current at the rated frequency of 50Hz, it is an indoor installed meter, Ambient temperature: -10 to 50℃, relative humidity: below 80%(25℃).DT-8 and DT862 series three phase meter is an induction meter to measure the three phase current at the rated frequency (50Hz) it is an indoor installed meter; Ambient temperature: -10 10 to 50℃,relative humidity: below 85%(25℃).