{TAIL ~ This device} mainly comprises a relay , a transistor , {HEAD ~ an optical coupler} , and a tapping/rectifying circuit  
{ TAIL ~ This device } mainly comprises a relay , a transistor , { HEAD ~ an optical coupler } , and a tapping / rectifying circuit
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH