Page 180 - Mechanical Engineers' Handbook (Volume 2)
P. 180

5 Optical Methods  169








































                                                 Figure 25 Fiber-optic radiation probe.



                           which in turn delivers it to the signal processor. The low-temperature fiber can be of great
                           length, without degrading the signal, since loss coefficients for the low-temperature fiber
                           material are quoted in percent per kilometer.
                              The processing of the radiant signal can be discussed in terms of the system pattern
                           function: a set of equations that show how the system is supposed to work. The pattern
                           function for the fiber-optic system is presented below. A final calibration adjusts the output
                           to bring it into conformance with the calibration results.
                                        I (T )       CC (
, T )
                                                      1
                                                             i
                                                        d
                                                                                  i
                                                                            i
                                           i
                                                0 
 [exp(C , 
T)   1]  F(
)BS(
, T )LTF(T ) d
  (16)
                                                   5
                                                         2
                           and
                                                    I   I K sensor K cable K detector F(T )     (17)
                                                                         i
                           where I (T )   detector current, pattern function
                                   i
                                 I(T )   actual detector current, corrected for T i
                                   i
                                   
   wavelength
                                   T   temperature, K
                                   T   temperature of signal processor box
                                    i
                                  C   radiation constant: 3.743   10 ,W  m /m 2
                                                               8
                                                                      4
                                   1
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