Selection and Testing of Electronic Components for LM

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122 Fig. 16 Fault detector shelf and fault detector and service unit. The instrument units are placed to the left in the shelf and the attenuation of the fault location pair. A maximum of 32 housings can be connected, on condition that the attenuation is less than 40 dB. The power feeding is carried out from the supervising station using parallel feeding. This permits branching of the fault location pair. The fault location equipment in the repeater housing consists of the fault detector and service unit, which also contains the speaker circuit equipment. All housings are equipped with identical units and the address identity is determined by means of straps. At the terminal the fault location equipment is assembled in a fault detector shelf of the M5 single shelf type, fig. 16. The shelf can accommodate the abovementioned unit for supervising the terminal repeaters in the bay. In the supervising terminal the shelf is also equipped with the instrument units, including power equipment, required for the fault location. The received error rate is indicated by a light-emitting diode strip. The error pulses are also available on a counter and a recorder output. The housing and repeater addresses are set up with thumb-wheel switches. Each fault detector shelf can terminate and monitor six fault location pairs. The unit is prepared for control from an external computer which makes possible automatic supervision. Fault location equipment ZAD 2 — 3 The fault location method with filter 2 used in the previous system generation has been retained in the 2 Mbit/s equipment. A mechanical adaptation to the new system has been carried out. In the intermediate repeater stations the fault location filter has been combined with the speaker circuit unit, and this unit can also be placed in the terminal in a fault location shelf. The fault location shelf, a M5 single shelf, can accommodate two fault localisation filters, and terminate up to six fault location pairs. The shelf can also accommodate one line terminating equipment, a facility that has been provided to cater for small stations where there is only one PCM system. The reasons for retaining the filter method were that it is simple and that many administrations have access to the required measuring instruments. It is, however, possible to adapt ZAD 2-3 to the fault location system of ZAD 8-2.
Fig. 17 The instrument "2 Mbit/s line test set" lor investigating whether cables are suitable tor PCM transmission. Practical operating conditions can be simulated and evaluated with the aid of this instrument Locating of cable faults in ZAD8-2andZAD2-3 In the case of cable breaks it is possible to locate the fault in the cable with the aid of the power feeding. The power feeding unit is then switched over to voltage feeding with reversed polarity. A current contribution is obtained from each repeater before the break point and the faulty repeater section can be singled out by measuring the sum current at the terminal. If the cable fault consists of a short circuit between the two pairs in the power feeding loop the fault can be located by measuring the output voltage. Line test sets LM Ericsson have developed special instruments, line test sets, for 8 Mbit/s and 2 Mbit/s digital line systems, in order to simplify planning, installation and fault tracing. The two instruments have the same general structure and each consists of a transmitter, receiver and accumulator with a charging device. Fig. 17 shows the 2 Mbit/s line test set, which is now in production. The various parts are combined into one robust mechanical unit. The transmitter can generate bipolar pulse trains, one of which is crystal controlled. The receiver consists of a modified one-way repeater, supple 123 mented by a bipolar error detector and a counter. The modification makes it possible to control the equalizer and the position of the decision thresholds manually. The transmission quality of the cable can be checked with the instruments by measuring the error rate, cable attenuation and eye opening. The last test provides a measure of the efficiency of the equalization and of any reflections. With the 8 Mbit/s instrument it is also possible to check the strapping chosen in the equalizer with regard to the type of cable. The instruments can also be used for crosstalk measurements or for checking the effect of external disturbances such as signalling disturbances. During these measurements it is often only the end points of the cable that are accessible, i.e. no working signal can be applied to the receiver. Through a unique property of the instruments the result can be obtained in the form of an equivalent error rate. Alternatively the noise power at the decision point can be measured. The interpretation then assumes a knowledge of its amplitude distribut ion. Summary When developing the digital pair cable systems ZAD 8-2 and ZAD 2-3 experience from the previous generation of 2 Mbit/s line systems has been utilized
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
Page 12 and 13: Fig. 12 Computer-controlled test sy
Page 14 and 15: 104 Fig. 16 Comparison of fault tra
Page 16 and 17: Fig. 2 Cable groups with the conven
Page 18 and 19: 108 Fig. 9 Take-up stand lor connec
Page 20 and 21: Insulation: Solid polyethylene Cond
Page 22 and 23: New Telephone Set Arne Boeryd and G
Page 24 and 25: Digital Line Equipments for 8 Mbit/
Page 26 and 27: Fig. 5 ALBO network for automatic e
Page 28 and 29: Fig. 8 Block diagram of the line te
Page 30 and 31: Fig. 13 Small repeater housing of t
Page 34 and 35: 124 References 1. Lindquist, S. and
Page 36 and 37: LARS G ERICSSON AKE PERSSON Telepho
Page 38 and 39: 128 Fig. 3 Standardization of progr
Page 40 and 41: 130 Fig. 6 The control room in an A
Page 42 and 43: Table 3 Number of component faults
Page 44 and 45: 134 ence this as congestion or a "s
Page 46 and 47: ABJ 101-the Modern Public Magneto S
Page 48 and 49: Fig. 3 Line unit for 10 magneto lin
Page 50 and 51: " The maximum number of lines that
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Selection and Testing of Electronic Components for LM

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