Fiber Optic Temperature Sensors
About the fiber optic temperature sensors
Fiber optic cables can be used as
temperature sensors in various ways, although special attention has to
be paid to providing a suitable protective coating when high
temperatures are measured. Two out of many examples of fiber optic
temperature sensors are the fiber optic cross-talk sensor and special
types of fiber where the temperature-sensitive refractive indices of
the core and cladding are almost equal. Further examples are the
phase-modulating fiber optic temperature sensor, and forms of monomode
fiber which modulate the polarization of the light transmitted
according to the temperature.
One extremely accurate form of extrinsic fiber optic sensor is a
device known as the Accufibre temperature sensor. This is a form of
radiation pyrometer which has a black-box cavity at the focal point of
the lens system. A fiber optic cable is used to transmit radiation
from the black-box cavity to a spectrometric device which computes the
temperature. This has a measurement range of 500°C to 2000°C, a
resolution of 10-5°C and an inaccuracy of only ±0.0025% of
full scale.
Fiber optic cables are also frequently used to transmit light into
standard radiation pyrometers from a remote targeting lens. The cables
can be used in all types of radiation pyrometer, including the
two-color version. However, it is not possible to use fiber optics for
measuring very low temperatures because of the attenuation along the
fiber of the very small radiation levels which exist at low
temperatures. The minimum temperature which can be measured is about
50°C, and the light guide for this must not exceed 600 mm in length.
At temperatures exceeding 1000°C, lengths of fiber up to 20 m can be
successfully used as a light guide.
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Temperature Measurements
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