Stray lines

The emission spectrum from a hollow cathode lamp includes, besides emission lines for the analyte, additional emission lines for impurities present in the metallic cathode and the filler gas. These additional lines serve as a potential source of stray radiation that may lead to an instrumental deviation from Beer s law. Normally the monochromator s slit width is set as wide as possible, improving the throughput of radiation, while being narrow enough to eliminate this source of stray radiation. 

Accuracy When spectral and chemical interferences are insignificant, atomic emission is capable of producing quantitative results with accuracies of 1-5%. Accuracy in flame emission frequently is limited by chemical interferences. Because the higher temperature of a plasma source gives rise to more emission lines, accuracy when using plasma emission often is limited by stray radiation from overlapping emission lines. 

The Berlin City electrical engineer M. Kallmann reported in 1899 on a system for controlling stray currents of electric railways [64]. As early as 1894, the Board of Trade in London issued a safety regulation for the British electric railways which specified a potential differential of not more than 1.5 V where the pipeline was positive to the rails, but 4.5 V with the rails positive. Extensive research was undertaken on reducing the risk of stray current in the soil by metallic connections from pipes to rails. However, as one writer noted, a procedure on these lines should definitely be discouraged as it carries the seed of its own destruction [64]. 

If the projected pipeline is situated in an area with dc railway lines, rail/soil potential measurements should be carried out at crossing points and where the lines run parallel a short distance apart, particularly in the neighborhood of substations, in order to ascertain the influence of stray currents. Potential differences at the soil surface can give information on the magnitude of stray current effects in the vicinity of dc railway lines. It is recommended that with existing pipelines the measurements be recorded synchronously (see Section 15.5) and taken into account during design. 

The railway lines on bridges are often electrically connected with steel or reinforced steel structures which usually have a very low grounding resistance. In new installations, an electrical separation of the rails from the bridge structure is required according to the grounding resistance of the structure and the type of rail bed. Independent of this, pipelines and metal sheathing of cables are always electrically separated from the structure in order to exclude direct transmission of stray current from the rails in these conductors. 

External lines are generally found only in outlying districts and between different cities. Of considerable importance in reducing stray currents and keeping... 

Stray Currents from High-Voltage dc Power Lines... 

Figure 15-2a shows the stray current interference by a bipolar high-voltage dc power line [7]. When the system breaks down, large voltage cones occur in the soil at the grounding installation. A few kilometers away, the current density in the soil is relatively low. 

Fig. 15-5 Stray current interference in the region of dc railway (a) Polarization of the railway lines, (b) voltage between the soil in the vicinity of the rails against a remote ground. Polarization of the pipeline (c) without stray current drainage, (d) with stray current drainage without a resistor, (e) with stray current drainage via a resistor R. Current in the pipeline (f) without stray current drainage, (g) with stray current drainage.

Electrical sources static electricity, electrical current, lightning, stray currents (radiofrequency electromagnetic radiation, overhead high voltage transmission lines, galvanic and cathodic protection stray currents)... 

The foregoing paragraphs refer particularly to stray d.c. from railways, tramways, trolley vehicles, mobile cranes and similar systems where the running rails or metallic supports are in direct contact with the earth. Underground d.c. tube railways usually operate on the fourth rail system and may be enclosed within cast-iron tube linings so that there is little or no stray current. 

Stray currents Railway lines Cable break Arc welding... 

Abstract. We present preliminary results of an extensive low and high-resolution ESO-VLT spectroscopic survey of Subgiant stars in the stellar system uj Centauri. Basing on infrared Ca II triplet lines we derived metallicities and radial velocities for more than 110 stars belonging to different stellar populations of the system. The most metal rich component, the SGB-a, appears to have metallicity [Fe/H] -0.5. Moreover, SGB-a stars have been found to stray from the dynamical behaviour of the bulk population. Such evidence adds new puzzling questions on the formation and the chemical enrichment history of this stellar system. 

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