Owfeel SM852B 3 Phase Sequence Presence Rotation Tester Indicator Detector Meter With LED And Buzzer 60V~600V AC Used to measure the opening phase condition and sequence through LED and Buzzer. Used to check if current sequence on the 3 phase circuit is correct through Buzzer and LED. One Unit with 2 Functions: Open phase indication and phase rotation indication. Frequency range : 20Hz to 400Hz, red, green, yellow light indicates the buzzer. Measuring frequency range: 20Hz to 400Hz;continuously usage time: 200V ACVin 60mins,600V ACVin 4mins