| 摘要 |
<p>The light beam in an obstruction detector is coded into packets of pulses by a transmitter. When the light beam is received, the receiver recovers the code signal and supplies it to a code detection circuit. To detect the code, the circuit supplies the code signal and a delayed version of the code signal to an "exclusive or" gate. If the code is present, the gate produces a pulsed output resulting in a "safe" signal being sent to a door opener control circuit. If no code is present, the gate produces a relatively constant output resulting in an "unsafe" signal being sent to the door opener circuit. The "unsafe" signal is produced not only in response to obstructions, but also, in response to errors and malfunctions in the wiring to the transmitter and receiver and in the transmitter and receiver themselves. <IMAGE></p> |
