[time-nuts] Pendulum Clock Synchronization

Brooke Clarke brooke at pacific.net
Thu Mar 5 12:55:42 EST 2009


Hi:

The Western Union clocks made by the Self Winding Clock Co. have a provision 
for hourly synchronization of the hour, minute and second hands using a pulse. 
   Since there were many thousands of these in service they are constantly on 
eBay. See:
http://www.prc68.com/I/SWCC.shtml#Sync
http://www.prc68.com/I/SWCC2.shtml#SC

When they were used in government buildings, banks, jewelry stores, etc. the 
line voltage was 120 VDC and the current was adjusted to 250 ma with a variable 
resistor.  Note that the time constant of an LR circuit is proportional to L/R 
so raising the voltage allows adding resistance speeding up the circuit.  This 
is mandatory in teletype circuits and makes a big improvement in the operation 
of the synchronizing circuit for a clock or operation of a slave clock.

Since it's only one pulse per hour I've started looking into using a free power 
supply that runs on a single AA cell.  The problem with these is that the 
voltage is about 300 VDC, but that may be OK if current limited to 250 ma (abut 
1200 Ohms).  See:
http://www.prc68.com/I/LED.shtml#SUCFBO

-- 
Have Fun,

Brooke Clarke
http://www.prc68.com





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