Fiberoptic Sensor Instrumentation

The excitation pulse tram is used to trigger of the excitation. Mode-locked lasers and cavity-dumped lasers are versatile excitation sources however, they are not ideal to implement portable instruments. Externally modulated solid state microlasers are a 

The procedures cited in each box of the flux diagram are discussed below.00, 21) 

SET AND ENABLE CLOCK FREQUENCY to be divided by the programmable counters or synthesizers. 

LOAD COUNTERS The load and hold registers of the programmable counters I and 2 are loaded to produce variable duty cycle pulse trains. The values loaded to the counters are determined by Eqs. (9.103) and (9.104). 

DISABLE INTERRUPTS to allow the dedication of the microprocessor to the data acquisition without interruptions in order to maintain synchronization during the data collection. 

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Most probably, the first - but non-fiberoptic - sensors for continuous use where those for pH and for oxygen. It has been known for decades that cellulosic paper can be soaked with pH indicator dyes to give pH indicator strips which, however, leached and thus were of the "single-use" type. The respective research and development is not easily traced back since it is not well documented in the public literature. However, in the 1970s, indicator strips became available where they pH indicator dye was covalently linked to the cellulose matrix, usually via vinylsulfonyl groups. These "nonbleeding" test strips allowed a distinctly improved and continuous pH measurement, initially by visual inspection. In the late 1980 s instruments were made available that enabled the color (more precisely the reflectance) of such sensor strips to be quantified and related to pH. Respective instruments are based on the use of LEDs and are small enough to be useful for field tests in that they can be even hand-held. This simple and low cost detection system is still superior to many of the complicated, if not expensive optical pH sensors that have been described in the past 20 years. 

Krohn DA (1988) Fiberoptic sensors fundeunenteils and applications, vol 138. Instrument Society of America, Research Triangle Park, NC... 

Optical fibers and the instrumentation used in fiberoptic chemical sensors are described in Section II. We describe how different optical phenomena, generated by different sensing mechanisms, can be applied to optical fibers to measure analytical signals. These sensing mechanisms are described in Section HI. Section IV reviews several fiber-optic chemical sensor analytical applications in the clinical, industrial, and environmental fields and Section V reviews recent developments in fiber-optic chemical sensors. 

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