Patent ID: 8063790

Claim:
A system for detecting the presence of an object, the system comprising: a transmitter operable to switch between on and off states to respectively activate and deactivate emanation of a detection signal from the transmitter along a path; a receiver positioned to receive a reflection of the detection signal from off the object when situated proximate the transmitter in the path of the detection signal and generate a measurement signal in response to signals received by the receiver; and a controller connected to the transmitter and the receiver to control switching of the transmitter between the on and off states, to selectively receive the measurement signal and associate a measurement value therewith, and to establish a range of values around the measurement value spanning from a lower range limit below the measurement value to an upper range limit above the measurement value; the controller being arranged to perform at least one state-change test in each of which the controller receives a first measurement signal from the receiver with the transmitter in a respective one of the on and off states, associates a first measurement value with the first measurement signal, establishes a first range of values around said first measurement value, receives a second measurement signal from the receiver with the transmitter in a respective opposite one of the on and off states, associates a second measurement value with the second measurement signal, and determines whether the second measurement value falls inside the first range of values, which indicates absence of the object in the path of the detection signal proximate the transmitter.