handbook of modern sensors

16.4 Optical Temperature Sensors 493
(A)
(B)
Fig. 16.24. Fluoroptic method of temperature measurement: (A) spectral responses of the excitation
and emission signals; (B) exponential decay of the emission signal for two temperatures
(T 1 and T 2 ); e is the base of natural logarithms and τ is a decay time constant. (Adapted from
Ref. [13].)
(B)
(A)
Fig. 16.25. Placement of a phosphor compound in the fluoroptic method: (A) on the surface of
an object; (B and C) on the tip of the probe. (Adapted from Ref. [13].)
(C)
temperature range from −200 ◦ Cto+400 ◦ C. The measurement of time is usually the
simplest and most precise operation that can be performed by an electronic circuit;
thus, temperature can be measured with a good resolution and accuracy—about ±2 ◦ C
over the range without calibration.
Because the time constant is independent of excitation intensity, a variety of
designs is possible. For instance, the phosphor compound can be directly coated onto
the surface of interest and the optic system can take measurement without a physical
contact (Fig. 16.25A). This makes possible the continuous temperature monitoring
without disturbing a measured site. In another design, a phosphor is coated on the tip
of a pliable probe which can form a good contact area when brought in contact with
the object (Figs. 16.25B and 16.25C).