Optical electrical signals

Techniques, such as spectroscopy (Chapter 10), potentiometry (Chapter 11), and voltammetry (Chapter 11), in which the signal is proportional to the relative amount of analyte in a sample are called concentration techniques. Since most concentration techniques rely on measuring an optical or electrical signal, they also are known as instrumental techniques. For a concentration technique, the relationship between the signal and the analyte is a theoretical function that depends on experimental conditions and the instrumentation used to measure the signal. For this reason the value of k in equation 3.2 must be determined experimentally. 

The first detector for optical spectroscopy was the human eye, which, of course, is limited both by its accuracy and its limited sensitivity to electromagnetic radiation. Modern detectors use a sensitive transducer to convert a signal consisting of photons into an easily measured electrical signal. Ideally the detector s signal, S, should be a linear function of the electromagnetic radiation s power, P,... 

Optical connectors ate used to terminate and interconnect fiber optic cables (see Fiber OPTICS). Transmission of information by light through optical fibers made of glass or plastic is less expensive in many cases than transmission of electric signals through wire. An advantage of fiber optic technology is that it is... 

All ctfecis caused by electrostatic or electromagnetic inductions are termed Inductive Interferences. With the use t)f glass optical fibre cables in new installaiioiis. this effect is overcome automatically. Optical fibre cables, as discussed later, have no metal content and cany no electrical signals. Therefore the above discussion is more appropriate for existing installations and also to provide a theoretical aspect and moi c clarity on the phenomena of inductive interferences. These can also be applied to other fields rather than communications alone. 

Collecting optics, radiation detectors and some form of indicator are the basic elements of an industrial infrared instrument. The optical system collects radiant energy and focuses it upon a detector, which converts it into an electrical signal. The instrument s electronics amplifies the output signal and process it into a form which can be displayed. There are three general types of instruments that can be used for predictive maintenance infrared thermometers or spot radiometers line scanners and imaging systems. 

Optical fibres are not yet very much in use, but there is no interference between them and electrical signals of any sort. For this reason their use will probably become more widespread. Line-of-sight optical signals require that no obstruction is inserted at any time. Such points are easily noticed when installing and commissioning, but are not so obvious if a malfunction occurs at a later date. 

Optical methods are especially useful for the selective detection of CO and C02 concentrations. In low-priced sensors, a simple miniature light bulb is used as IR-source. The radiation emitted enters an absorption chamber, through which the flue gas is pumped. An added interference filter lets only the absorption spectra of the target gas pass. The IR detector determines the reduction of the light intensity, which is then transformed into an electrical signal. The correlation between the source intensity and the received intensity is given in the Lambert-Beer equation. 

Whole cell silicate sensors14 will soon make use of the viability of cells and their ability to respond to external conditions, using genetically engineered cells tailored to emit measurable optical or electrical signals. The operation principle is shown in Figure 6.15. 

In fluorescent molecular sensors, the fluorophore is the signaling species, i.e. it acts as a signal transducer that converts the information (presence of an analyte) into an optical signal expressed as the changes in the photophysical characteristics of the fluorophore. In contrast, in an electrochemical sensor, the information is converted into an electrical signal. 

The transducer converts the reaction between the analyte and the biological component into an electrical signal which is a measure of the concentration of the analyte. A wide range of transducers are available and are broadly divided into electrochemical, optical, thermal and piezoelectrical. 

Detectors are used to convert X-ray flux into an electrical signal, which can then be digitized and stored. For imaging cabinet X-ray systems, the detectors usually consist of a folded linear array of scintillators optically coupled to photodiodes. Typically, 500-1000 such detector elements are present for single-energy imaging... 

The IR intensity of IR flares is measured by using a radiometer which consists of both optical and electronics systems. The radiometer uses the optical system consisting of mirrors and lenses to collect the radiation emitted by the object and focuses this radiation upon an IR detector which converts it into an electrical signal. This signal after amplification is processed by the computer system where it is stored. This stored data can be displayed on the monitor and printed. 

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