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An update on timekeeping and accuracy

Aug 04, 2015

Hi everybody!

One of the things I like to do is to validate the quality of my work occasionally. I recently did a long term timing accuracy test of one of my 30cm WordClocks.

The test started on 20 May 2015, and ran through to 2 August 2015 – a total of 75 days (6,480,000 seconds) – I set the clock to the correct time (against a GPS standard), and I measured the time change every couple of days. I am pleased to announce that in those 75 days, the clock maintained the correct time to within 96 seconds (one minute and 36 seconds). That is a wonderful effort from a simple quartz oscillator.

Hang on – Am I saying that not keeping time is a good thing – Isn’t that really a bad thing???

Actually, no – In the clock business accuracy is very important, but that has to be measured against some realistic goals. Time is relative (I have been waiting ages to say that!) There are some beautiful timepieces that maintain accuracy, such as;

  • Citizen Chronomaster with the A660 module which is specified at about 5 seconds p/y accuracy
  • ETA thermoline – 10 seconds per year
  • Seiko 8J/9F  – 10 seconds per year
  • Citizen E510 – 10 seconds per year

These are all beautiful timepieces that are worthy of mention – and they also cost significantly more than my clocks do.

Yes, there are clocks that have GPS receivers installed in them and that allows them to maintain time in the order of 10 seconds per 500 years, but these have to have external antennas and modules to allow the GPS signal to be received.

So… My clocks use a quartz crystal, which is specified at 20 parts per million in accuracy, so 96 seconds over 75 days works out to about 1.28 seconds per day, which I consider to be insignificant. It certainty is not noticeable when the display is updated every 5 minutes 🙂 We have to stay sane when it comes to super accurate timekeeping.

I also know in Europe and the USA, that there are low frequency time standard sources that can be used to automatically set clocks, such as;

  • RTZ in Irkutsk/Russia
  • MSF in Britain
  • WWVB in the USA
  • RBU in Moscow/Russia
  • HBG in Prangins/Switzerland
  • DCF77 in Mainflingen/Germany

Each of these services is able to be received by a $5 module that allows a clock to be automatically set – What an awesome idea!!! Here in Australia we used to have our own time standard station (VNG) located in Victoria, but sadly our sheep farming, coal mining, non technologically focused federal government decided to close that station down, removing the ability to cheaply synchronise clocks within Australia. So all we can use use is GPS technologies to synchronize clocks. – Oh well…

Now – I am not discounting GPS based clocks, I think they are neat. One of the things I would like to do is to look at the feasibility of adding a GPS receiver option to my 30 cm and above wall clocks. It will add a small optional cost to the clocks for the GPS receiver and antenna, but would be a very interesting thought.

Let me know what you think in the comments below.

Doug

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4 Comments

  1. Deborah Says: August 4, 2015 5:07 pm

    I’ve been toying with adding a serial protocol to my Arduino-based clocks (of which one is a Doug’s) to keep the time on spec. I’ve weighed up various competing options, one of which is GPS, and they all suffer from the same flaw: they only tell you UTC, not your local time. Governments can and do change time zones at short notice, especially if you broaden the concept of “time zone” to daylight saving changes.

    What I’m leaning towards is to plug a Bluetooth module onto the Arduino’s serial port and have a nearby computer periodically resynchonize the time. If the computer is connected to an NTP source it has accurate time, and if it’s getting regular software updates it knows the correct time zone. The protocol could be a great deal simpler than GPS NMEA, to boot.

    Time is hard. Case in point: that 75-day period had a leap second in the middle of it, so it was actually 6480001 seconds.

    Reply
    • DougJackson Says: August 4, 2015 10:20 pm

      Ahhh – yes, there was a leap second….. I completely forgot 🙂

      I like the concept of a bluetooth module or something that talks wifi to get the time from a local computer.

      Doug

      Reply
      • Jared Says: July 11, 2016 1:44 am

        I added a temperature compensated clock a few years ago and it drifts a second or two a year.

        Reply
  2. Bryan Sweeney Says: September 8, 2016 7:43 am

    I recently acquired a MobaTime Swiss train station style wall clock. It has a GPS receiver that connects to my internet router in my home. It works flawlessly. When the power is out it resets itself. When I contacted MobaTime about this, it would seem that the GPS reciever doesn’t cost much money.

    I am assembling a wall of clocks where accuracy of each clock is essential. If one is off, then it is quite noticable. Having a GPS reciever would alleviate this issue. The GPS reciever I got from MobaTime has DIP switches so it displays the time for my time zone.

    Reply

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