|P.O. ENGINEERING DEPT.
Issue 3, 22.9.59
Clock No. 17A - Description
Clocks No. l7A are used with associated apparatus (see Dgm. AT 2041) to give half-hourly audible warnings in telephone exchange
switch rooms of nine or more working positions during traffic call-counts. In new exchanges fitted with master clocks (Clocks No. 36) Clocks No. 62A are used in place of Clocks No. 17A (see B 1342).
2. Description of clock
Clock No. l7A is an 8 day mechanical lever-movement, housed in a rectangular mahogany case. The movement is wound from the front, and the winding key is kept inside the case. The clock is provided with a small circular dial divided into 60 divisions and has only one hand.
3. Description of movement
The movement consists of two spring-driven time trains. The first is a lever and escapement-controlled train, driving the single hand H. The second, which has no escapement, drives cam D which operates contacts C.
Cam A, attached to the axle of hand H, operates the lever arms B and BB at half-hourly intervals, when the hand is in the position equivalent to 6 and 12 o’clock. The operation of the levers B and BB releases the time trains associated with the cam D, which in turn operates contacts C. The contacts C close, and complete the bell circuit for approximately 3 seconds.
|Diameter of dial
|Depth (back to front)