Abstract: An object detection system employs a photo-emitter and photo-detector for synchronously detecting and processing an optical signal reflected from an object in a pinch zone of a window or door opening. A photo-emitter light signal is modulated by a modulation signal having an active phase and an inactive phase. The optical detector provides an optical detector signal that is a function of the intensity of the received light. The detected light signal is synchronously detected using a switching amplifier that multiplies the reflected modulated light signal by a first gain during the active phase and by a second gain during the inactive phase. The duration of the active and inactive phases and the first and second gains are selected such that the system gain will average to zero for ambient light when integrated over a predetermined measurement period. The synchronously detected signal is subtracted from a predetermined offset voltages and this difference is then integrated over the measurement period.

Abstract: A monitoring system for use in detecting the presence of an obstacle in or proximate to an aperture. Materials are applied to one or more reflecting surfaces adjacent the aperture, enabling the improvement of the signal-to-noise ratio in the system without requiring tuning the system for the particular environment. The choice of specific material depends upon the type of radiation used for aperture monitoring and whether an obstacle is detected as an increase or decrease in reflected radiation. A calibration LED within the monitoring system enables predictable performance over a range of temperatures. The monitoring system is also provided with the capacity to adjust to variations in the background-reflected radiation, either automatically by monitoring trends in system performance or by external command. The latter case includes the use of a further element for communicating to the monitoring system directly or indirectly.