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The day that time stood still on campus

Who changes more than 3,000 clocks in offices, classrooms when standard time returns?

Time stopped at The University of Texas early on the morning of Oct. 28, for one hour.

The hands on the four faces of the clock atop the Main Building Tower and on classroom clocks all over campus stood still as the campus converted to Central Standard Time.

To change the clocks manually would require hours, maybe days. There are more than 3, 000 of them in offices classrooms and other facilities on campus.

But with a specially engineered central system, a handful of men need only flick a few switches to change them all.

The same central system keeps those clocks running, accurate to within a minute, by tying their operation to pulses broadcast by short-wave radio station WWV in Colorado.

Every minute, the station broadcasts a special tone, which the system translates into an electronic pulse. That pulse triggers the movement of the hands on the clocks.

Almost 30 floors above the ground, the 33-year-old Tower clock responds to the pulse. The pulse moves a lever, which allows a gear to rotate. That slight rotation is conveyed to all four faces simultaneously.

Worked Faithfully Since Mid-1930's

Saleem Tawil, communications engineer for the Physical Plant, said the clock mechanism in the Tower was installed when the Tower was built in the mid-1930's and has worked faithfully since.

A set of weights on a chain provides the stored energy to operate the clock. With each pulse, the weights drop a fraction of an inch. When thy reach the floor, once or twice a day, a small electric motor lifts them to the top of the chain to repeat the cycle.

The electricity used by the huge clock thus costs only about 30 cent a day, Mr. Tawil estimates.

The Tower chimes which ring every quarter-hour are tied into the clock mechanism, using simple mechanical gears to trigger hammers to ring the correct bells. An electronic keyboard, far below in the Main Building, is used to play tunes on the bells.

The Pulses Are The Key

Should the broadcast tone not be received, a master clock will send out pulses on its own across campus. And should it fail also, five "sub-master" clocks on campus can keep pulses going to clocks in their areas, Mr. Tawil explained.

The pulses are the key. Without them, most of the wall clocks and even the tower clock would stop. The wall clocks have no time-keeping mechanisms of their own behind their faces.

Early on the morning of Oct. 28, Physical Plant employees stopped all the clocks by merely disconnecting the receiver, master clock and the five sub-masters on campus. An hour later, they reconnected them.

In the spring, switching to Daylight Saving Time is even simpler, Mr. Tawil explained. Employees need only increase the number of pulses going to the clocks until they have gained an hour's time. It takes only minutes.

The semi-annual changes provide a good opportunity to check clocks for accuracy, Mr. Tawil said.

Under the pulse system, they should be within one minute of the exact coordinated universal time used by the Bureau of Standards, he said.

On Campus. November 5-11, 1979.
Article by: Martha Chamberlain

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3 May 1999
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