TRAFFIC CONTROL TELEPHONE SYSTEMS Circuit - Sam Hallas

Page 22
Thus:
17 minus (1st digit + 3rd digit) = 2nd digit.
= 17 minus (3 + 3) = 11 impulses.
Commencing at the 17th impulse K1, 2 and 3 are in contact for a period of 2 to
3 seconds during the ringing period, then K1 and 2 open, but K1 and 3 remain in
contact, holding the battery relay until the key arrives at the normal position. On the
opening of K1, K2 contacts the reversing relay is de-energised and an impulse is
transmitted which releases the selector called and any other selector which may have
held on an intermediate code pin. When the key arrives at the normal position and K1,
K3 open, the battery relay is released and an ineffective impulse is transmitted. The
system is now at normal and ready for further calls.
General Call
To set the key to call all stations seventeen uninterrupted impulses are sent to
line. These impulses advance all selectors, irrespective of the position of their code
pins, to the 17th step which is the ringing position. Thus the call bells at all Way
Stations are energised calling all the operators.
This is done by using two flat segments bridging all teeth from the top of the
ninth tooth to the ringing position.
Time Sending
In this case 22 successive impulses are transmitted which advance all selectors
to the time bar. To do this use a flat segment bridging from the centre of the first tooth
to the centre of the fourth tooth.
Mechanical Requirements for Maintenance Purposes
1. The main spring M and shafts where exposed, should be greased lightly with
petroleum jelly to Standard Spec. 50518. Appendix No. 1.
2. Pinions to be very lightly oiled with oil dag to Standard Spec. 50227.
3. Governor bearings to be very lightly lubricated with clock oil to Spec. 57544
Grade 2.
N.B. - It is important that this should be done carefully, as any oil on the
governor weights will affect the speed of the key.
As a guide to what is intended by the term "very lightly oiled" the following
definition will be of assistance.
"To apply oil very lightly, insert a pointed match-stick in the oil and allow the
amount of oil picked up by the match-stick to drain on the part to be lubricated."
We suggest that oiling is made a routine job every three months.
The above mentioned oils are obtainable from Standard Telephones and Cables
Ltd. in 1 pint, 2 pint, ½ and 1 gallon cans.