Selection and Testing of Electronic Components for LM

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108 Fig. 9 Take-up stand lor connection wire Fig. 7 Binding head and length measuring device Fig. 8, right Take-up stands for 10-pair groups Random pulse generator The random pulse generator, fig. 5, utilizes the white noise in a transistor to generate randomly distributed pulses for the mixer. Mixer, cross stranding device Fig. 4 shows the cross stranding of a 10-pair group. The pairs are taken through dies which move sideways in the cross stranding device. The movements of the dies —the mixing of the pairs —are controlled by a motor that is started and stopped by pulses from the random pulse generator. The pairs are fanned out over rollers, after which they are assembled and bunched together. There is no systematic order between the pairs because their positions on the rollers are changed at random. Binding head The purpose of the binding head is to fix the pairs in the same order that they have when leaving the mixer, fig. 7. The binding yarn can be used for identification purposes. A binding head usually has an electromechanical binder yarn break detector. The mechanical part of the detector has a sensing finger which is easily broken, thereby causing the machine to stop. The break detector in the cross stranding line binding head has therefore been redesigned and is fully electronic. The binder yarn tension can be adjusted during operation. Length measuring device Fig. 7 also shows the length measuring device, including the tachometer which synchronizes all drive motors of the whole line. Take-up stand Any type of take-up stand can be used for 10-pair groups. Fig. 8 shows a type of take-up stand where all drive equipment is placed on a frame above the drum which leaves the floor free for the transportation of drums. A drum twist takeup is recommended for 25-pair groups. Final assembling A conventional stranding machine with a drum twist take-up can be used for the final assembly. It need only be equipped with a few stands for pay-off reels and can thus be simple. No back-twist of the individual groups is required. Supplementary equipment Fig. 3 shows an ordinary cross stranding line. Accessories for various purposes can be included in the line, such as taping heads for different taping materials. If the group twinner is supplemented with a specially designed pay-off and take-up device it will be suitable for simultaneous twinning and coiling of connecting wire on small bobbins. Ten
Fig. 10 Distribution curves, showing the capacitance unbalance of 10-pair groups Insulation: Solid polyethylene Conductor diameter: 0.5 mm Cable length: 500 m Curve A represents approximately 1000 capacitance unbalance values within 10-pair groups in cross stranded cables manufactured In the Plteä plant during 1976. Curve B represents approximately 1000 capacitance unbalance values within concentric (2 + 8) 10-pair groups. The shaded area shows the reduction of high capacitance unbalance values obtained by introducing the cross stranding technique. The expected reduction for other curves B (due to the techniques used tor the wire drawing, twinning etc.) can be calculated approximately by shifting the shaded area Fig. 11, right Distribution curves, showing capacitance unbalance between and within 10-pair groups Insulation: Solid polyethylene Conductor diameter: 0.5 mm Cable length: 500 m Curve A represents the capacitance unbalance between 10-pair groups In cross stranded cables Curve B represents the capacitance unbalance within 10pair groups in cross stranded cables bobbins with pairs and triples or five bobbins with quadruples and quintuples can be manufactured in one operation. The take-up device is shown in fig. 9. Cross stranding line It has already been stated that since the group twinner consists of several individual twinning machines, special care was devoted to making the design reliable and simple. Thus the 10-pair group twinner has twenty pay-off shafts, each with its own brake. The risk of a breakdown because of a brake fault is then multiplied by twenty and hence the group twinner is equipped with reliable, simple rope-brakes. Size of reels It is generally considered that large pay-off reels give high efficiency, but experience shows that there is an optimum size. Too large reels give rise to such disadvantages as conductor elongation, long acceleration and retardation times etc. Most factories in which the introduction of cross stranding lines is contemplated are already provided with pay-off and take-up drums. It must therefore be possible to adapt the cross stranding equipment for use with a wide range of such drums. Space requirements A cross stranding line requires less floor space than conventional equipments, 109 owing to the fact that the pair twinning and group stranding is carried out in a single operation. The group twinner alone requires much less space than the corresponding number of single twinners even if these are of the high-speed type. Operation In the group twinner all twinning heads are idle during reloading. This factor has a negative effect on the efficiency compared with production using the corresponding number of single twinning machines. A loading table for pay-off reels has therefore been included in the cross stranding line in order to reduce the loading time. A 10-pair line has to be reloaded every third to fourth hour and the reloading time is only ten minutes. Owing to the compactness of the line and the smooth operation one operator is sufficient for the supervision of three 10-pair lines. However, it is desirable that two operators work together when reloading. Electrical characteristics of cross stranded cables Capacitance unbalance The cross stranding technique reduces the high unbalance values between the pairs and the crosstalk characteristics are improved to a corresponding degree since no pair combinations are permitted to be systematically adjacent during any large part of the cable length. This is shown in fig. 10.
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Page 42 and 43: Table 3 Number of component faults
Page 44 and 45: 134 ence this as congestion or a "s
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Page 48 and 49: Fig. 3 Line unit for 10 magneto lin
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Selection and Testing of Electronic Components for LM

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