Fibre-optic cables

The use of TRDs has been facilitated by the use of fibre-optic cable assemblies (Section 6.12.4). This permits sensing in confined spaces as well as enabling the sensor to see round corners and into regions containing nuclear or electromagnetic radiation 36 . Low levels of source visibility can be overcome by employing two-colour or ratio sensors which measure radiation at two different wavelengths simultaneously. Such instruments can be used where dust or dirt obscures the source from the sensor. 

The continuous monitoring of can be obtained by using a fibre optic cable attached to the pipe itself or to the structural elements connected to the pipe. The fibre can act as a simple data transmitter (insensitive fibre) or be itself a sensor for its total length or for only selected sector (sensitive fibre). The different possibilities are presented in Figure 4. 

Simply stated, fibre-optic cable allows for the transfer of light from one point to another without going in a straight line, and as such their use in process analytical applications is highly seductive. In a likely NIR process application there may be multiple sample stream take-offs, each with different sample characteristics, located in positions spread around a process unit, with the only apparently convenient analyser location some distance away. 

Figure 3.34 Internal reflection and acceptance angle in a fibre-optic cable.

The maximum input acceptance angle for a fibre-optic cable is determined by the critical angle for total internal reflection, which is given by Snell s law. 

An interesting modification of this technique is the fibre-optic dynamic anemometer (FODA)143. A length of fibre-optic cable carries the laser beam to the interior of the dispersion. Back-scattered light, with its Doppler frequency shift, is returned to the detector along with reflected light and, again, the resulting beat frequency pattern is analysed. Since only a very small volume around... 

Optical sensors display several advantages over electronic sensors. Since photons rather than electrons carry the information, they are almost immune to electrical interference. Usually the optical components are made from glass chips or fibre-optic cable fibres, giving them excellent mechanical and thermal stability and often, moreover, a high chemical resistivity. Finally the use of glass, especially fibre-optic, fibres helps to minimise the size and weight of these sensors. Optical sensors, especially fibre-optic sensors have been the subject of several recent reviews [116-120]. 

A block-scheme of this apparatus is presented in Fig. 2.12, A and B. Compared to that given in Fig. 2.11, an adequate improvement is the use of fibre optic cable which conducts the light from Hg-Xe arc lamp to the reflected light microscope. The thickness is determined by the microinterferometric technique of Scheludko-Exerowa (see Section 2.1). 

The desire to combine the advantages of conventional multicompartment electrolysis cells and the simultaneous collection of spectroscopic information has led researchers to the use of bifurcated fibre-optic cables that connect the electrochemical cell to a remote spectrometer. Source radiation is guided into the analyte solution and returned to the detector by the reflective working electrode surface or a mirror with adjustable separation from the source. Setups for optical and IR spectroscopy have been described and successfully employed to address the issue of chemical reactivity coupled to electron transfer. 

Use of NIR energy as the mode of information transport provides the potential for high signal throughput and the use of fibre optic cables over long distances for... 

It is becoming clear that to meet the OEM s requirements which now nearly always have a combination of problems, these problems will be resolved by building up the substrate as the circuit is produced. Different layers will be added to cope with high speed signals, or to stiffen the board or to modify the thermal expansion. Heat removal will be done through heat pillars or openings in the dielectric. In Japan, fibre optical cables are being... 

The pathlength for IR samples is in the range 2-3 mm. Gases are easiest to sample in a longer pathlength cell, typically 10 cm in length. Fibre optic cables can be used where the sample is remote from the spectrometer. 

The MonARC FTIR system from Mettler Toledo identifies and quantifies chemical species based on changes in the fingerprint region of their IR spectrum. It also has a built-in ultrasonic cleaner for the diamond sensor which increases reproducibility and reduces downtime. Various types of fibre optic cable and probe heads are available depending on... 

Ray diagram for light passing down a fibre optic cable, showing the limiting ray that just undergoes total internal reflection, nf = 1.65, = 1.50, numerical aperture = 0.69,... 

Gilmore, M., Fibre Optic Cabling Theory, Design and Installation Practice, Newnes, Oxford, 1991. 

Laser Fluorimeter As 2i source of biological information we propose the use of a multi-station (up to 12 sampling locations) towed sea water laser fluorimeter for water quality analysis specific to selected hydrocarbons which might be present in the area. The laser excites elements of the plankton population and that of calibrated hydrocarbons (e.g. breakdown products of munitions contents) present in the water. The fluorescent spectra are received through a fibre optic cable, split and counted through specific filters. From this data a direct correlation of the effects of pollution on the plankton population can be made. The system would be towed in conjunction with the multi-sensor towed array. 

To provide power for construction and equipment, two 15 kV power feeds and fibre optic cables were routed up one of the main legs using cable tray. One of the 15 kV feeds was allocated to power the hoist and the other was used for construction and equipment power the power was stepped down using one of the undergroimd transformer sleds. To outfit the... 

High voltage power supply to the underground mine—1 IkV system Communication system fibre optic cable route... 

The introduction of fibre-optic cable systems and digital transmissions will undoubtedly affect future cabling arrangements and the work of the electrician. 

The energy is transferred down the cable as digital pulses of laser light, as against current flowing down a copper conductor in electrical installation terms. The light pulses stay within the fibre-optic cable because of a scientific principle known as total internal refraction which means that the laser light bounces down the cable and when it strikes the outer wall it is always deflected inwards and, therefore, does not escape out of the cable, as shown in Fig. 3.42. 

Fibre-optic cables look like steel wire armour cables (but of course they are lighter) and should be installed in the same way, and given the same level of protection, as SWA cables. Avoid tight-radius bends if possible and kinks at all costs. Cables are terminated in special joint boxes which ensure cable ends are cleanly cut and butted together to ensure the continuity of the light pulses. Fibre-optic cables are Band I circuits when used for data transmission and must therefore be segregated from other mains cables to satisfy the lET Regulations. 

The testing of fibre-optic cables requires special instruments to measure the light attenuation (i.e. light loss) down the cable. Finally, when working with fibre-optic cables, electricians should avoid direct eye contact with the low-energy laser light transmitted down the conductors. 

Computer installations, fibre optic cables and data cabling provide speedy data processing and commimications. 

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