| Microwave digestion is a newly developed method for the preparation of sample. It has been used in various fields including biology, coal industry, metallurgy, food industry, environment protection, medicine industry and so on. Temperature is always the key point of the microwave digestion instrument. The monitoring to the sample temperature in the microwave digestion instrument is the key technique all the time. It's one of the difficulties at the same time.In recent years, the technique of fiber temperature sensor was applied to the microwave digestion instrument gradually. The virtues of the fluorescence optical fiber temperature sensor are electromagnetic interference resisting, little bulk, low transmission loss, corrosion resisting.Based on thoroughly analyzing to the present research at home and abroad, we have designed fluorescence optical fiber temperature measuring system applies to microwave digestion instrument.The basic principle and characteristic of fluorescence measurement method are discussed, and the total scheme of fluorescence optical fiber temperature measuring system is designed. Based on the fluorescence specific properties of ruby crystal are analyzed, the system adopts the LED as excitation light source in order to gain more advantages than that of the traditional method such as configuration, control mode and lifetime. With the optical fiber link, it forms optical fiber fluorescence temperature sensor. The blue LED is adopted as the excitation light source in this system. The sensor brings periodic fluorescence decay signal under the excitation of a series of light pulse from LED. After having been detected, the signal is amplified by a low noise wide band amplifier firstly. Then every decay curve is digitized. The method of least squares curve fitting is used to make the best exponential fitting curve with these data. Finally, comparing the value of the time constant with the data comparison sheet, the temperature of the sensor can be confirmed.
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