Example A Temperature Sensor

The measurement of temperature is necessary for the calibration of most probes like blood oxygen, pH, ions, voltage, and carbon dioxide sensors. The use of optical methods to invasively measure physiological temperature has the advantage of electrical isolation, when compared to traditional approaches like the use of thermocouplers. 

The fluorescence and phosphorescence of luminescent materials are modulated by the characteristics of the environment to which these materials are exposed. Consequently, luminescent materials can be used as sensors (referred also as transducers or probes) to measure and monitor parameters of importance in medicine, industry and the environment. Temperature, oxygen, carbon dioxide, pH, voltage, and ions are examples of parameters that affect the luminescence of many materials. These transducers need to be excited by light. The manner in which the excited sensor returns to the ground state establishes the transducing characteristics of the luminescent material. It is determined by the concentration or value of the external parameter. A practical and unified approach to characterize the luminescence of all sensors is presented in this chapter. This approach introduces two general mechanisms referred as the radiative and the nonradiative paths. The radiative path, in the general approach, is determined by the molecular nature of the sensor. The nonradiative path is determined by the sensor environment, e.g., value or concentration of the external parameter. The nonradiative decay rate, associated with the nonradiative path, increases 

Wolfbeis, Fiber Optic Chemical Sensors and Biosensors, Vols. 1 and 2, CRC Press, BocaRaton (1991). 

Wise and L. B. Wingard, Biosensors with Fiberoptics, Humana Press, Clifton, NJ (1991). 

Chemical Sensors and Microinstrumentation (R. W. Murray, ed.), ACS Symposium Ser. 403, American Chemical Society, Washington, D. C. (1989). 

---

The location and type of sensor can greatly affect controllability, safety, and on-time reliability. Controllability can also be improved when a different type of sensor is used. For example, a temperature sensor might be used to infer composition. Such a sensor is easy, robust, and accurate in measuring the temperature. However, the new specifications for the purity have shifted the composition to a range where temperature measurements are no longer sensitive to the composition. Refractive index measurements should be used. 

---