Nobody really thinks about automatic doors. Which is precisely the idea. You have groceries in your hands, your arms are full, your brain is busy, the door simply moves. It senses the situation like a skilled waiter who refills your drink unprompted. It is an unexpectedly complex of sensors, motors, safety logic and building code regulations that all react within half a second behind that effortless reaction. Although invented in the 1960s, modern systems are far removed from their primitive beginnings. Automatic doors have evolved into precise, reliable tools found everywhere because they work so well people forget they exist. 
The brain of the entire operation is the sensor. Typically, these doors use overhead-mounted microwave sensors or passive infrared detectors, or PIR. PIR sensors detect body heat signatures as people pass. Microwave sensors send signals and read the reflection. Each has trade-offs. PIR can struggle with drastic temperature shifts, such as cold entrances that mask heat differences. Microwave sensors are more consistent, though they can be Discover triggered by debris or even a passing bird. Very busy installations frequently combine the two technologies, making cross-checks on signals prior to commanding the motor to act. The outcome is a minimized amount of false triggers and a reduced number of doors that simply sit there with their mouths open as everybody inside of it freezes. Motor systems have also developed eminently. Early doors relied on basic electromechanical setups with relays and simple timers. The brushless DC motors are used today with variable speed controllers. Doors now glide open, slow near full extension, pause, and close gently. Gone are the abrupt bangs of earlier designs. Software now ensures the door reverses upon encountering resistance. This is not a luxury feature. Regulations such as EN 16005 and ANSI/BHMA require this behavior by law. Any door that closes on a child or a wheelchair user and continues to push is not a door, but a motorized hazard.
The brain of the entire operation is the sensor. Typically, these doors use overhead-mounted microwave sensors or passive infrared detectors, or PIR. PIR sensors detect body heat signatures as people pass. Microwave sensors send signals and read the reflection. Each has trade-offs. PIR can struggle with drastic temperature shifts, such as cold entrances that mask heat differences. Microwave sensors are more consistent, though they can be Discover triggered by debris or even a passing bird. Very busy installations frequently combine the two technologies, making cross-checks on signals prior to commanding the motor to act. The outcome is a minimized amount of false triggers and a reduced number of doors that simply sit there with their mouths open as everybody inside of it freezes. Motor systems have also developed eminently. Early doors relied on basic electromechanical setups with relays and simple timers. The brushless DC motors are used today with variable speed controllers. Doors now glide open, slow near full extension, pause, and close gently. Gone are the abrupt bangs of earlier designs. Software now ensures the door reverses upon encountering resistance. This is not a luxury feature. Regulations such as EN 16005 and ANSI/BHMA require this behavior by law. Any door that closes on a child or a wheelchair user and continues to push is not a door, but a motorized hazard.