Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1988-10-11
1990-04-03
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356 731, 356301, 330 43, 250214A, G01N 2100
Patent
active
049142887
DESCRIPTION:
BRIEF SUMMARY
This invention relates to optical sensing systems of the kind in which successive optical pulse signals of a particular wavelength are transmitted along an optical fibre sensor which extends over a path the temperature profile or some other profile (e.g. loss profile or pressure profile) of which is required to be monitored. Time-related back-scattered light resulting from the pulses propagating along the fibre sensor may be detected and measured by means of an optical time domain reflectometer which accordingly provides an indication of the temperature distribution along the fibre sensor.
The utilization of back-scattered light for determining the profile of a physical parameter causing variations in the scattering of light along the fibre sensor enables optical fibres to be monitored either to check their basic transmission characteristics or, alternatively, to monitor external physical parameters, such as temperature, along the fibre.
However, the back-scattered returned signals along the fibre sensor are generally relatively weak. Consequently, a high degree of signal averaging of the return signals in response to successive optical pulses propagating along the fibre sensor is required in order to establish an accurate scattering distribution measurement,
The present invention is directed therefore to a fast multi-channel averaging circuit arrangement which enables the back-scattered return signals from a large number of points along the optical fibre sensor to be stored as each of the successive optical pulse signals propagates along the fibre and which facilitates the subsequent averaging of all the return signal stored data to provide an accurate measurement of the scattering profile along the fibre sensor.
According to the present invention there is provided a multi-channel averaging circuit arrangement, especially for use with optical sensing systems of the kind described above utilizing back-scattered light return signals for establishing the scattering profile along a fibre sensor, in which the circuit arrangement comprises a plurality of charge-coupled-device arrays each consisting of a multiplicity of devices capable of storing all the successive elements of a signal waveform (e.g. corresponding to the return optical signal of back-scattered light in an optical sensing system), in which the charge-coupled-device arrays are arranged to be rendered operative sequentially for storing successive incoming signal waveforms under the control of timing means and in which, following the storage of a predetermined number of signal waveforms in the respective charge-coupled-device arrays, the groups of signal waveform elements data stored in devices of the charge-coupled-device arrays are fed sequentially into an averaging circuit, preferably including resistor/amplifier means and in which the averaged groups of signal elements are preferably fed into an analogue-to-digital converter, prior to being fed into a processor for providing an indication of the averaged signal waveforms in respect of the successive incoming signal waveforms to the circuit arrangement.
In carrying out the present invention for the averaging of the returning optical signal waveforms from an optical fibre sensor in optical sensing systems in response to the succession of optical pulses propagating along the fibre, the returning optical signals may be applied to an avalanche photodetector for converting the returning optical signals into electrical signals and these electrical signals may then be amplified before being fed to the charge-coupled-device arrays sequentially under the control of clock means which also controls the triggering of a laser which produces the successive light pulse signals for propagating along the fibre sensor.
BRIEF DESCRIPTION OF THE DRAWING
The FIGURE shows a circuit arrangement according to the invention.
By way of example the present invention will now be described with reference to the SINGLE-FIGURE accompanying drawing which shows a signal waveform averaging circuit arrangement eminently suitable
REFERENCES:
patent: 4123160 (1978-10-01), Caputo et al.
patent: 4236904 (1980-12-01), Lazay
patent: 4399458 (1983-08-01), Berry et al.
patent: 4713538 (1987-12-01), Theocharous
Murphy et al., "An Attenuation Monitor for Use in Optical Cable Field Trials", Int. Wire & Cable Symposium Proc., 11/81, pp. 396-405.
Shibata et al., "Measurements of Waveguide Structure Fluctuation in a Multimode Optical Fiber by Backscattering Technique", IEEE Jour. of Quantum El., 1/81, pp. 39-44.
Hillerich, "On Site Location of Optical Fiber Defects and Eval. of Transmission Loss", Int. Wire & Cable Symposium Proc., 11/77, pp. 373-379.
Michaels, "Time-Domain Reflectometers Tackle Fiber-Optic Cabling", Electronics Design, vol. 34, No. 18, 8/86, pp. 59, 60, 62.
Messinger Michael
Nelms David C.
Plessy Overseas Limited
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