Patent ID: 6236038
Filing Date: 2001-05-22
Classification: G01V

Abstract:
An optical barrier unit configured to provide an optical barrier, said optical barrier unit being provided with a unique identification number made up of hexadecimal digits and comprising:one or more first modules each including M first light elements configured to at least emit light and a corresponding number of second modules, each second module including N second light elements configured to at least receive light, M and N being positive integers; andat least a first control circuit configured to control the one or more first modules so that the M first light elements of each of the one or more first modules emit light beams modulated with different coded words having different binary bit arrangements of a same number of binary bits that have durations of high and low binary values that are equal or nearly equal, said different coded words including,a first type of coded word having a number of predetermined pairs of said binary bit arrangements corresponding to the number of first modules being used in the optical barrier unit, wherein each one of said number of predetermined pairs of said binary bit arrangements uniquely identify which one of the number of first modules the light beam modulated with the first type of coded word is associated with and further indicate a first binary coded word value or a second binary coded word value, anda second type of coded word having only two different predetermined binary bit arrangements that indicate the first binary coded word value and the second binary coded word value,wherein said at least a first control circuit causes each of the one or more first modules present to emit modulated beams in a particular manner relative to the first light elements therein with at least one predetermined one of the modulated beams emitted by each of the one or more first modules present being modulated with one of the predetermined pairs of binary bit arrangements of the first type of coded word so that the at least one predetermined one of the modulated beams emitted by each of the one or more first module present uniquely identifies the corresponding first module while also providing one of the binary coded word values as part of a code indicating the identification number of the optical barrier unit, andwherein any other modulated beams being emitted by each of the one or more first modules present are modulated with one or the other of the two different predetermined binary bit arrangements of the second type of coded word by the at least a first control circuit so that particular binary coded word values are further provided to complete the code indicating the identification number of the optical barrier unit.