TRAFFIC CONTROL TELEPHONE SYSTEMS Circuit - Sam Hallas

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Page 26 CODE TABLE No. 2 (Key System only)
Cycle of Events on Receiving a Code Taking the same code as used in the description of the 4001-A Selector Key, viz.: 3-11-3, the sequence of events is as follows : On operating the selector key the battery relay of the system is operated, connecting the line battery to the line, and remaining operated during the complete revolution of the key. The initial operation of the battery relay sends an isolated impulse (not included in the 17 coding impulses) which energises all selectors on the line giving a flick to the holding spring, thereby releasing any selector which might have been held on a coding pin. The first-set of impulses from the calling key are reproduced by the impulsing relay which gives three impulses of alternating polarity to the line. These three impulses advance all the selectors three steps. Then, although the battery is held on the line the condenser in series with each selector (see Fig. 1) stops the flow of current and the armatures of all selectors release. The code wheels of all selectors, then return to normal except those coded with three as the first digit, these are held in position by the holding spring K (Fig. 10). All selectors are then advanced by the second set of impulses, 11 in this case. Of the selectors that were held in an advanced position before, only the one called will now have a code pin in the second pin position to be engaged by the holding spring, because there would be only one station on the line with the first digit of three and second digit of eleven. The selectors that returned to normal after the first digit and which have a first digit of 11 will be in position to be held by the holding spring. All other selector code wheels will restore to normal during the pause of approximately one second after the second digit. A total of 14 impulses have now been received and the selector under consideration is therefore held at the 14th step. The third set of impulses, three in number, advances all selectors three steps. Only the selector that had its code pins in the code wheel set for 3-11-3 (the selector called) will have reached the permanent code pin or ringing position, that is, a total of 17 steps from the normal position. In this position the contact spring on the top of the code wheel will be directly over the first ringing terminal and making contact with it. Some of the selectors may be held on the first code pin, but will not have advanced to the third or ringing code pin. It will be seen therefore that all selectors respond to the impulsing but only the one coded to correspond with the code transmitted reaches the ringing position. During the ringing period of approximately two seconds, a ring-back tone is heard by the Controller or other receiver across the line while the call bell is ringing. Referring to Fig. 1, the ring-back circuit is as follows: L1, .02 μF capacitor through the selector contacts, ringing battery, bell contacts, .02 μF capacitor, L2, controller's telephone and back to L1. Page 27
Page 2 and 3: TRAFFIC CONTROL TELEPHONE SYSTEMS C
Page 4 and 5: CONTENTS Part Title Page 1 Key Syst
Page 6 and 7: swing of the meter needle either si
Page 8 and 9: One No. 4002-B Selector Key Case (c
Page 11 and 12: wires. This change of polarity is t
Page 13 and 14: Case), K2 terminal (Time Sending Se
Page 15 and 16: Where satisfactory operation cannot
Page 17 and 18: one is available (if not, with an o
Page 19 and 20: PART 2 4001-A SELECTOR KEY Selector
Page 21 and 22: The keys are easily removed from th
Page 23 and 24: Letter. Name. S.T.C. Code. A Impuls
Page 25 and 26: 4. When the key is normal the tip o
Page 27: the time terminal. During selective
Page 31 and 32: Mechanical Requirements To assist i
Page 33 and 34: (b) The contact spring (Z) in the n
Page 35 and 36: Letter Name 4301-A 4304-A 4305-B A
Page 37 and 38: General PART 4 4001-B SELECTOR TEST
Page 39 and 40: 4001-B Selector Test Set, Schematic
Page 41 and 42: General PART 5 DIAL SYSTEM, SELECTI
Page 43 and 44: The speak key also connects the con
Page 45 and 46: normal, Relay IR is held operated a
Page 47 and 48: here that from SC bank contacts 29
Page 49 and 50: from Line switch SC banks 1 and 2 a
Page 51 and 52: Line Test Set . . . . . . Designed
Page 53 and 54: Line Voltage Curves Fig. 14. The op
Page 55 and 56: General PART 7 LINE TEST SET-LU.310
Page 57 and 58: Operating Instructions 1. Voltage M
Page 59 and 60: the particular line to the earthed
Page 61 and 62: Operate CVK, note meter reading on
Page 63 and 64: 10. Impulse Ratio Check on Selectiv
Page 65 and 66: 12. Telephone Communication. (See F
Page 67 and 68: Page 65
Page 69 and 70: Armature Travel Armature travel is
Page 71 and 72: Contact Sequence The standard conta
Page 73 and 74: chloride or trichlorethylene. The t
Page 75 and 76: PART 9 ADJUSTMENT AND MAINTENANCE D
Page 77 and 78: 9. Armature Restoring Springs:— T
Page 79 and 80:
Oil dag should be applied as above
Page 81 and 82:
3. Pawl Spring Tension 3.1 With the
Page 83 and 84:
8.6 The wipers shall exert a pressu
Page 85 and 86:
2.2 The wipers shall rotate smoothl
Page 87:
Registered Office: CONNAUGHT HOUSE
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TRAFFIC CONTROL TELEPHONE SYSTEMS Circuit - Sam Hallas

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