The guide-rail harmonic meter with external roche coil and open type mutual inductor is suitable for energy saving renovation projects in high energy consumption industries such as smelting,steel,electric welding,semiconductor,etc.And also for power monitoring of distributed photovoltaic grid-connected cabinet,power demand side management and other applications.The utility model has the advantages of no need to remove primary bus,simple and convenient wiring,safe construction,saving transformation cost and improving efficiency for users.It integrates the measurement of all power parameters(such as current,voltage,active power,reactive power,apparent power,frequency,power factor,etc.),multi-rate electric energy measurement,four-quadrant electric energy measurement,harmonic analysis and electric energy monitoring and assessment management.At the same time, it has a variety of peripheral interface for user to choose:with RS485 communication interface,modbus-rtu protocol can meet the needs of communication network management;The function of “remote signal” and “remote control” of circuit breaker switch can be realized with switch quantity input and relay output.LCD display interface is adoped to realize parameter setting and control through panel keys,which is very suitable for real-time power monitoring system