Selection and Testing of Electronic Components for LM

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104 Fig. 16 Comparison of fault tracing costs at various check levels. (Micro circuits) Volume checked: 2 000 000 Volume checked: 10000000 Development tendencies The component development is at present progressing very rapidly, particularly in the field of micro circuits. There are already so many types of circuits for different purposes that existing demands for speed, low power consumption, insensivity to disturbances or voltage variations can usually be satisfied. However, because of the rapid development of micro circuits there has often been time for improved circuits to appear on the market during the period between the selection of components and the putting into service of the first example of a new system. It is desirable that it should be possible to exploit new achievements in the field of components in previously completed designs, for example by changing over to a new circuit family. The development of micro circuits leads to an increasing degree of complexity and flexibility. This means that the boundaries between components, units and subsystems are being wiped out. Programmable component types, such as micro processors and memories, will have a decisive influence on the design and performance of the systems. This also means that a greater part of the "knowledge" and flexibility of the exchange systems will be transferred from fixed hardware to changeable software. As regards memory components the development is towards greater capacity and speed. It is likely that the memory types that retain the information even in the case of voltage failures will become very important in future. It is also likely that selectors with mechanical contacts will to an increasing extent be replaced by electronic switching elements. Opto-electronic and purely optical components will also be very important for the transmission of information. Development of passive components follows in the wake of the applicable material and production engineering development in the semiconductor field. The resistors will be able to withstand higher voltages and will have smaller dimensions. There are already resistor networks that are mounted in micro circuit packages. It is also likely that plastic foil, oxide and ceramic capacitors will be improved.
Cross Stranding of Telephone Cable Sigurd Nordblad LM Ericsson have developed a new manufacturing process and constructed new machines for the manufacture of pair cables. The process, which is called cross stranding, combines two methods: twinning and stranding of groups in one operation and repeated changing of the relative positions of the pairs during the stranding. The changing can either be carried out systematically in accordance with a set plan or at random, so-called randomized cross stranding. The main purpose of the cross stranding is to reduce the extreme values of the crosstalk and thus improve the quality of the cable. In the article the cross stranding technique is described with the emphasis on the manufacture of pair cables with randomized changing, but cross stranding can also be used with advantage for stranding single conductors, triples, quads, quintuples etc. The cross stranding technique has now been introduced at most of the telecommunication cable factories owned by the Ericsson Group. At the Piteå plant, which wasstartedin 1972, the entire production is based on this technique. Manufacturers outside the Group also use the technique. UDC 621.315.2 621.391.31 Fig. 1 Cross stranded cables Top, 150-pair cable with 25-pair groups Bottom, 50-pair cable with 10-pair groups, jelly- In addition to line attenuation, characteristic impedance and line resistance, the crosstalk characteristics of a cable have a very great influence on its field of use. This applies particularly in the case of trunk cables but also for subscriber cables. One reason why the subscriber cables of today should have a low level of crosstalk is that modern telephone sets can then be utilized more efficiently. The usefulness of a telephone set is limited by such factors as the crosstalk level in the cable network. A reduction of the crosstalk means that greater distances can be spanned or that the conductor size can be reduced. High frequency systems, which are used nowadays to an ever increasing extent, SIGURD NORDBLAD Sieverts Kabelverk AB also require cables with improved electrical characteristics. Previously the pairs, single conductors, quads etc. of a cable have usually been assembled in concentric layers. The pairs were then parallel in each layer and were adjacent to the same pairs along the whole length of the cable. Subsequently the unit cable was introduced, but the units were still built up of concentric layers. Efforts to improve the cable characteristics have been concentrated on improving the precision of the wire drawing, insulation etc. and on suitable selection of lay lengths, i.e. improvements within the pairs, and very little attention has been paid to the effect of the cabling method on the electrical characteristics. Crosstalk occurs mainly between adjacent pairs and it is obvious that the crosstalk increases when the pairs are adjacent over a long distance. Using the conventional layer stranding technique the pairs are placed adjacently and as close as possible along the whole length of the cable. The crosstalk level between pairs varies in a cable; high level between adjacent pairs and very low level between separated pairs. However, in a telephone system the worst values often constitute a technical limit and a number of very good values does not alter this fact.
Page 1: ERICSSON REVIEW 3 1977 SELECTION AN
Page 4 and 5: Selection and Testing of Electronic
Page 6 and 7: Fig. 2 Curve tracer The special typ
Page 8 and 9: Fig. 6 Humidity test High air humid
Page 10 and 11: 100 Type of check Type of component
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Page 44 and 45: 134 ence this as congestion or a "s
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