Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1987-05-04
1989-03-28
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356 731, H01J 516
Patent
active
048166693
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a process for signal processing of reflected pulses for time localization of these, in particular in connection with reflection measurements where at least two reflected pulses are received, the first one of which originates from a predetermined reference point, the second one from a reflection point whose position is to be determined.
The said reflection point may be indicative of a rupture of a optical fibre, but may also be indicative of the end of the fibre, accurate determination of the length of optical fibres being important in connection with monitoring of the stress to which an optical fibre may be subjected in connection with cabling, winding of cables on drums, laying in the field or mechanical influences. Further, measurements of lengths and changes in the length are extensively used by fibre manufacturers when manufacturing the optical fibres and optical cables.
The above-mentioned measurements have previously been performed by transmitting a plurality of light impulses in the optical fibre and then measuring the time lag between transmission of a pulse and reception of the associated reflected pulse.
The Norwegian Published Application No. 143 117 discloses a process for rough or fine determination of a reflection point on a transmission line. The location of the reflection point is determined by comparing the propagation time of a pulse on the transmission line under examination with the propagation time of a simultaneously transmitted pulse on a delay line.
In this process the entire transmission line is scanned in juxtaposed measuring intervals until the transmission line has been scanned along its entire length. This requires transmission of a large number of measuring pulses, which causes an examination according to this process to be very slow.
The object of the invention is to provide a process of the above-mentioned type, which enables significantly faster positional determination of the reflection point than was possible in the past.
This object is achieved by performing the process in which each measurement in a plurality of measurements comprises transmission of a pulse and examination of reflections of said pulse within two or more measuring intervals associated with the measurement and evenly spaced along the signal propagation path. The improved rate is obtained in that information can be received from several intervals during a single scan, which involves a reduction in the signal processing time, while permitting the use of slower and thus more inexpensive components in the apparatus used for performing the process.
To obtain a positional determination as accurate as possible, it is important that the entire reflected pulse constributes to the measurement, and the process is accordingly preferably performed in a process in which the positons of the intervals are shiftable, and that the positions are shifted if a reflection point is close to the borderline between two adjacent intervals.
The invention also concerns an apparatus for performing the process and of the type in which the apparatus comprises means for providing measurement pulses in response to a clock pulse signal, means for detection of pulses reflected from the propagation path, means for computing the time distance between a reflection point and a reference point and a store with a predetermined number of store locations corresponding to a plurality of detection intervals along the propagation path. The apparatus is characterized by the necessary and sufficient features to perform the process in which a store with a number of store cells each of which corresponds to a specific detection interval along the propagation path and having the detection means designed to store a signal in precisely the store cell which corresponds to the detection interval in which a reflective pulse is detected and including means scanning the store, said means being designed to initiate signal processing of the reflected signal in the interval which corresponds to a store cell with a predetermined content, the a
REFERENCES:
patent: 3900261 (1975-08-01), Wingate
patent: 3981592 (1976-09-01), Williams
patent: 4344705 (1982-08-01), Kompa et al.
Aktieselskabet Nordiske Kabel-og Traadfabriker
Nelms David C.
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