Distributed Temperature Sensor
As the name implies, a distributed temperature sensor (DTS) is able to measure temperature as a continuous
function of position over an extended distance. The capability for long-range distributed sensing is unique
to optical fibres.
The basic principle of a DTS is analogous to that of radar. An optical pulse is transmitted along an optical
fibre light guide and a small part of the signal is scattered back along the fibre through interactions with
the glass. Knowing the speed of light in the optical fibre, it is possible to correlate the time of arrival of
the backscattered light with the position along the fibre at which the scattering occurred (see figure).
In the case of temperature sensing, the phenomenon of Raman scattering (where light is scattered through an
interaction with molecular vibrations within the glass) provides a convenient, temperature-dependent signal.
The early workers in the field used the well-known temperature dependence of the ratio between the powers in
the upper and lower sidebands of the Raman signal as the sensing mechanism. Later on, the instrumentation was
simplified by using only the anti-Stokes (high-frequency) signal, as this is the more sensitive of the two sidebands.
However, with this approach, it is much more difficult to apply corrections for errors associated with changes
in the optical fibre, transmitter and receiver characteristics. The proprietary Sentor® DTS technology solves
this problem by using a novel system characterisation procedure to periodically recalibrate the range fibre.
This provides all of the advantages of instrumental simplicity without any loss of measurement accuracy - thereby
reducing the overall cost.
The Raman scattering mechanism lends itself to applications where a precision of ±1°C is required. Temperatures can
be measured in a range from about -100 to 600°C, depending on the type of fibre cladding that is used. However,
within this broad specification, different applications may require different combinations of range and range
resolution (i.e. the shortest distance over which changes in temperature can be resolved). The DTS research programme
at Swinburne University of Technology (SUT) aims to address these various issues, while assisting with the
commercialisation of the Sentor 101® system.