... supply before operating,when the power supply is DC voltage,positive and negative can not be connected wronging,or ... concect the current transformerXXX/100V.4.Frequency meter , sampling AC voltage signal input value,(110V-380V), i.e. display the ... frequency value of the voltage,the dispay range of frequency is 30.0Hz-99. ... 0∼40 5.Watt-loss≤2VA 6.Maximum input AC voltage: 500V