Clock No. 24

Clock No. 24

The Clock No. 24 does not transmit impulses, but is arranged to operate external relays for line switching purposes and to provide the hourly current for time synchronizing signals.

In this clock a connecting spindle C, having bevel gear at the lower end, is driven from the count-wheel arbor.  A worm-gear at the upper end of the spindle operates switching apparatus, which consists of two discs A and B, controlling the positions of contact springs.  A, situated in front, rotates once an hour, and B (not shown in the illustration) situated behind, once in 94 hours.  The disc B controls contacts which form a change-over switch, allowing for connection or disconnection between either the 10 a.m. or the 1 p.m. group relays and the contact springs controlled by A.  The notch cut in the periphery of A allows the upper of the front pair of springs to fall and complete the circuit for 180 seconds in every hour.  On B, the tooth raises the centre one of the three springs at the rear at 10 a.m. and the notch drops it at 1 p.m.  The middle spring is permanently connected to one of the two springs over A and is normally disconnected from the spring on each side of it, so that unless it has been raised or dropped by B the circuit made hourly, at the A Spring is inoperative.  The disc A also carries an insulated pin D which once an hour depresses the lever S, closing the circuit for the transmission of hourly synchronizing signals.

When the clock has been fixed it should he adjusted so that the 24 hour disc is set to 10 a.m. This may be done by rotating the mechanism forward until the middle spring is approximately on the centre of the lifting cam; A should then be rotated independently of the train (after the grub-screw which lucks the disc on its arbor has been slackened) until the count wheel, being in a zero position, allows an equal distance (approximately 90 seconds) on each side of the notch.  In this way, the group of relays having been selected by B, the circuit is made by A from 1.5 minutes before the hour until 11 minutes after the hour.  The size of the notch in A should be such that the springs are disengaged before the circuit is again made on the next rotation of A.  Care should be taken in this operation to ensure that the mechanism is not rotated backwards, as reverse rotation would tend to buckle time middle springs and to damage the pawls of the count wheel and the pin on A.

At any local office where one of these clocks is used in conjunction with another clock between it and the Chronopher, it is necessary that time notch in A be adjusted in size locally so as to allow not more than 120 seconds for the total switching time. at the local office.  Otherwise there is a risk that telegraphic signals may interfere with the Time signal.  This adjustment may be done by filling the notch with a piece of brass cut to shape and recutting the notch.  The notch must be enlarged to 190 seconds if the clock is fixed next in order to the Central Telegraph Office, London, Chronopher.

The rotation of the disc A should depress the lever S and hold it and its spring to its contact screw F, for three minutes before the exact hour.  The duration of this contact may be varied by altering the screw F.  The circuit should, however, be opened exactly at the hour.

In order to correct any slight variation in the length of the lever S an adjustment is provided by means of the screw E; this moves the whole of this contact mechanism laterally in relation to the contact pin on the disc A.

The same precautions should be taken in erecting this clock as are set forth in detail under Clock, No. 12.

The details of the pendulum maintaining mechanism and synchronizer are similar to those of Clock, No. 12.

Diagram - GMT16.

Superseded by Clock No. 12.


BACK Home page BT/GPO Telephones Search the Site Glossary of Telecom Terminology Quick Find Clocks Home

Last revised: November 16, 2023