|P.O. ENGINEERING DEPT.
Issue 1, 8.10.38
ELECTRICAL CLOCKS - IMPULSE TYPE
Clock No. 30
Clock No. 30 is provided for use on impulse clock installations for the purpose
of synchronizing half minute secondary dials (see C 1002). It is connected in the clock circuit in the manner indicated on
Diagrams GMT 26, 34, 35, and 36.
Half-minute impulses energize the electromagnet M, which attracts the armature A to the left. This causes the pawl P3, attached to the extension of the armature, to be moved to the right and to engage the next tooth in the propelling wheel W. On the cessation of the impulse, a spring (not shown in the illustration) returns the pawl to its original position, thus carrying the propelling wheel forward one tooth, which is 1/120th of its circumference. Rigidly attached to the wheel W is an index disk Dl carrying, near its periphery, two pins P1 and P2. During the revolution of wheel W, these pins engage contacts Cl and C2. The pin P1, which is in contact with the frame, and situated near the periphery of Dl, makes contact with Cl for a period from
1.5 minutes before, to 4 minutes after, the hour. The springs carrying the contact Cl can, however, be adjusted to provide for the operation of Cl at one minute before, and one minute after, the hour. The spring and associated insulator are slotted for this purpose. This adjustment will only be necessary when the synchronizing signal is provided by a second sub-chronopher (see
C 1002). Three minutes before every hour, the pin P2 operates contacts C2 and C3, and allows them to break exactly at the hour. The propelling wheel W drives, by means of a 24 to 1 reduction gear, the 24-hour disk P2, which has on its periphery a projection at a point representing 10.0 a.m. and a detent at a point representing 1.0 p.m. Two sets
of springs having contacts Cl and C8, and C4, CS, and C6, are situated adjacent to the disk D2 in such a position that contacts C7 and C8 are made to operate a few minutes before 9.0 a.m. by the projection on the periphery of the disk P2, and contacts C4 and C5 are operated a few minutes before 10.0 a.m. Contacts C5 and C6 are operated a few minutes before 1.0 p.m. by the detent on the periphery of disk P2.
NOTE:- The contacts C7 and CS are situated in such a position relative to the disk D2 that they are operated exactly one hour in advance of the operation of contacts C4 and C5. The actual time the projection on P2 is opposite contacts C7 and C8 is, therefore, 9.0 a.m.
The internal connexions of the clock are shown on diagram GMT 36. The resistance of the electromagnet is between
7.5 and 10 ohms.
The clock is suitable for wall mounting and should be fixed in a position adjacent to the master clock
(Clock No. 36).