Norchard Clock Equipment

The clocks at Norchard are controlled by either of two ex GPO/BT pendulum master clocks. The operational clock produces pulses every two seconds, every six seconds and every thirty seconds. A locally designed relay set is used to interconnect the pendulum clock and the clock faces around the site.

We have several circuits feeding the slave clocks. The first circuit uses ordinary ex BT clocks which require a pulse of current every thirty seconds. These clocks are connected in series using the normal telephone cabling. This circuit connects the clocks close to the master equipment.

The second circuit uses ex Underground clocks which require a permanent current which reverses direction at every clock pulse. These clocks are connected in parallel using the normal telephone cabling. This circuit connects the clocks which are remote from the master equipment.

Clock pulses are also fed to Parkend, Norchard signal box and Lydney Junction signal box over one wire of a pair to earth. At present clocks are only fitted in our apparatus rooms, however, they seem to be very reliable and it may be that we will fit clocks in these remote public areas showing "Norchard Time". The other wire is used to relay alarm conditions from these outstations back to Norchard.

The equipment normally runs with thirty second pulses, but should the clocks need adjustment, there are advance and retard switches provided in the master clocks and in the shop to make the adjustments. Using advance, the clocks step every two seconds, using retard the clocks are stopped until time catches up with the clocks.

There are separate switches in both clock circuits which can isolate each circuit from the master clock. This facility is required should the two circuits get out of step as it allows either circuit to be stepped on or stopped independently.

Norchard Clock Control Equipment

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The above arrangements still hold but were recognised as being unable to provide much growth as we had no more reversal clocks available and we were going to be asked to provide clocks distant from the main building. A second relay set was constructed which will allow an ordinary pulse clock to be operated over a fairly long line. Such clocks are now referred to as auxiliary clocks. Nine auxiliary clocks are able to be connected to the relay set.

Norchard Auxiliary and Distant Clock Control Equipment

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Distant clocks are served by sending a battery pulse along one wire of a pair to the distant point eg Parkend station. The opportunity to put all the clock equipment into the new relay set was siezed and eight distant clock drivers are incorporated into the relay set. The clock pulses are monitored by the CPA - CPH relays. Normally the clock pulses show as a pulse on the alarm lamp on the relay set, but should a pulse not be monitored and the appropriate CP relay fails to operate, relay CC also fails to operate to the pulse. With the main pulse relay CR operated and CC not operated, relay CA operates and holds to the alarm reset link on the relay set. CA3 also lights the alarm lamp continuously to show that at some time a clock pulse has gone missing.

This work has removed all of the clock equipment out of the combined alarm/clock relay set. The relay set also holds the NU tone for spare levels relays which releases all of the non alarm equipment out the alarm relay set. This will permit the alarms to be rebuilt without any interference to the clocks.


Page provided by John Bathgate

This page was last updated on
17th February 2014