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Oryx DTS User Manual v4
Figure 29 - Typical construction of graded index multimode optical fibre
Signal Loss in Optical Fibres
All optical fibres experience a marginal loss of signal owing to absorption, radiation
scattering and reflection. This constant loss along the fibre results in the Stokes and
anti-stokes signals showing an exponential decay with distance. Step loss points
occur on or around joins (connectors or splices) or breaks in the optical fibre. The
overall loss of the signal within a length of optical fibre is expressed by its
attenuation coefficient, which is wavelength dependent. The DTS signal loss
typically has a value of 1.2 to 1.5dB/km at a wavelength of 975nm. This is the
wavelength of the light used in the Oryx DTS system. Signal loss is an important
consideration when designing and calibrating an optical fibre sensing network. The
known signal losses of the optical fibre are used to optimise the DTS system. See
the ODV section on page 82 for more information on measuring losses in fibre
cables.
NOTE: The light signal propagates along the optical fibre from the DTS system to
the end of the optical fibre and back again. This means the system will experience a
2-way signal loss of approximately 2.4dB/km in good fibre
Effect of Optical Fibre Cable on DTS Operation
It is usually necessary to place the bare optical fibres into cables for protection.
These cables offer increased protection from environmental, mechanical and
electrical damage and interference. When placing optical fibres in cables, there are
a number of factors to consider which will affect the choice of cable to use. These
are summarised below.
•
The cable will insulate the optical fibre from the environment being
measured. This will reduce the response time to fast temperature changes.
Summary of Contents for ORYX DTS
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