A system includes a mounting device (200), a detecting device (100), and a circuit (300). The mounting device includes a base (210), and a mounting head (220) opposite to the base. The detecting device is fixed on the base, and includes a shell (110) comprising a cavity (112) therein, a probe (130) fixed in the cavity and protruding towards the through hole, and a plug (150) having a pin (152) made of conductive materials. The shell further includes an opening (118) communicating with the cavity, and a through hole (114) formed opposite to the mounting head and communicating with the cavity. The pin is connected to the probe through the opening. The circuit includes a PLC circuit (320), and a power supply (310) connected with the PLC circuit. The pin connects with one of the PLC circuit and power circuit, and the mounting head connects with the remaining one.