How 3/4 Wing Automaitc Door Works ? The brief introduction below will be helpful to you to understand. 

1st，when acquisition sensor/detective radar in the canopy of the revolving door detects the infrared source like pedestrian, the signal will be sent to the PLC /main control unit of the door. 

2nd, The MCU /PLC process the signal from the radar, and sent the signal out from the corresponding ports, then the operation signal will be sent to the frequency converter and controls the output of alternating driving motor, and make the door revolve accordingly .

3rd, At the same time, the safety transducer, safety switch, emergency stopping button and other safety devices will monitor the signal, and send the signal to the PLC designated ports, if any of them be triggered,  PLC will send the braking signal to the frequency converter to make the motor stop immediately .