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Saturday, November 3, 2012

Government time standard via Web clock display

The above internet Web time clock display is provided by the U.S. Government National Institute of Standards and Technology (NIST) as a public service using the Flash Widget (See description page). It is a web clock showing the official time of day from NIST, displayed as a 12 or 24-hour clock, in a user-selectable time zone. The default time zone comes from the time zone setting on the client's computer, and it re-synchronizes with NIST every 10 minutes. It is very accurate, but is intended as a service only because it is not a traceable time standard, which is required for certain legal or scientific measurements and experiments. Note that links to a widget that works with more secure browser settings and the other government time service at will work with less secure browser security settings.

Everyone gets to change their clocks tonight by falling back one hour tonight. I have never understood Daylight Savings time and I know that dairy farmers in Minnesota have always hated it because cows don't change their schedules. Fortunately, this year I own some battery powered digital clocks that automatically receive the radio time signal from the U.S. government. They will reset themselves automatically.

Decades ago, the only time of day services available to the general public for setting their watches and clocks was wither the phone company's audio time of day message service, which could be listened to by calling a special phone number with any standard telephone, or by listening to the over-the-air radio signal broadcast by U.S. government's WWV station on the short wave radio band.

For some unknown reason, as a child I enjoyed calling the time of day phone number and later using by father's short wave radio to set my mechanical wind-up watch to the exact time. This is how I first discovered that my mechanical watch drifted by a minute per day whereas the wall clocks in my house, which were plugged into a 120V wall socket, would keep perfect time. My dad, being an old military radio technician, was able to explain to me the reason -- the electric power company, for various technical reasons, must keep the 60 cycles per second alternating current they generate exactly at 60 Hertz or suffer possible catastrophic failures of the power grid. As a result, electric clocks can be very accurate by using a gear driven synchronous motor that electro-mechanically counts the number of AC power cycles.

When electronic digital LED clocks first appeared in the 1970s, they were also able to count the power line cycles to generate very accurate time, assuming there were no power outages or noise on the power line. Of course, some of these problems can be solved with various circuit designs that also use battery backup, which can maintain the time during a power outage by courting the cycles generated by a small vibrating crystal in the clock.

Of course, keeping time by counting power line cycles requires the clock to be plugged into a known frequency, such as 60 Hertz AC power, which is standard in America. However, in Europe 50 Hertz is common and so digital clock makers must modify their clock for each country. In addition, other country's voltage standards range from 100 Volts AC to 240 Volts and more.

As a result, it can be an engineering challenge to design a wall plug that can be safely connected to and counted by low voltage digital clock circuitry. Meeting every country's safety regulations is an expensive process. To cut corners and cheapen things, too many digital clock makers today no longer count the AC power line frequency and instead use a cheap digital watch crystal to keep time, which is not very accurate.

I recently bought a Sony digital clock that plugs into the wall, but it drifts off time in a few months, probably because it is not counting power line frequency, but using a watch crystal.

I guess I'll see tonight if the above clock Widget resets itself correctly, which I assume it will.

On an unrelated note, I appear to have had more vision loss in the last few weeks and some other physical signs that are not good according to doctors -- I might become even less able to blog in the future. All I hope and pray for is that I have a peaceful death.