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Author Topic: Why do radio-controlled LCD clocks show different times?  (Read 6461 times)

Offline organmorgan

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Why do radio clocks show different time .I have seen this question on forum but no good answer.i have 4 clocks sat in a row getting good signals . After 3 overnight syncs they are different on average 1 sec . Two clocks the same .i am getting good signal.I can take photo showing them different. They are lcd so no hand slip . They are different makes with two of them the same . There is a difference between the two of same make .I think i have covered everything,
john
« Last Edit: 12/07/2009 20:43:54 by chris »


 

Offline RD

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Re: Why do radio-controlled LCD clocks show different times?
« Reply #1 on: 11/07/2009 19:55:25 »
They may not all synchronise their time with the radio signal simultaneously:
one clock may check its time with the radio once a day, another clock may check once an hour.
If hours pass between a particular clock synchronising its time with the radio signal then it could gain or lose a second in that period.

Quote
... Some clocks only decode the signal once per day, others do it more often (like every 4 hours or every 6 hours).
http://tf.nist.gov/timefreq/stations/radioclocks.htm
 

Offline Edster

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Re: Why do radio-controlled LCD clocks show different times?
« Reply #2 on: 11/07/2009 20:09:55 »
Sadly I can only speculate, as what is really needed is your location, and the makes and models of the clocks, also were they bought from the internet outside your country? All from the same supplier, or not?

As you say they are non analogue displays, that dispels what would have been my first suggestion, the hand calibration/zeroing.

Edit oops pipped on send by a detail post without the above info for us both to get a full story.
« Last Edit: 11/07/2009 20:17:02 by Edster »
 

Offline Edster

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Re: Why do radio-controlled LCD clocks show different times?
« Reply #3 on: 11/07/2009 20:37:40 »
A pretty average quartz mech does better than 10 seconds a month 5 is typical and 2 or 3 for people like seiko


If hours pass between a particular clock synchronising its time with the radio signal then it could gain or lose a second in that period.


1 second in a day is quite fishy (IMHO), but it could just be that sync capture window for the final part , the regular seconds info being genlocked is 10`s of milliseconds different and the basic movements seconds register is into another second when preloaded.

As i said all speculation ( and I`m sorry I can`t read the brands and models off that photo, I tried, just writing them down makes it easier  ;) )
« Last Edit: 11/07/2009 20:39:58 by Edster »
 

Offline organmorgan

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Re: Why do radio-controlled LCD clocks show different times?
« Reply #4 on: 11/07/2009 20:44:20 »
Thanks for reply guys. i have no idea what edit oops pipped on send line means though.
I accept all your points and of course there is no way i can verify these points. How ever taking the radio clock/watch concept as a whole it is a bit of a let down. Until i had 4 clocks i thought the one was sacrosanct and perfect time . This new  info blows a hole in the concept of radio time being what most people will think of it. I am going to check them against my garmin GPS now but im not sure if it gives secs i shall see.
To my thinking that if it gives secs could say which of the 4 is correct ?
cheers john  ps you have to be in your 70s to worry about things like this !
 

Offline RD

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Re: Why do radio-controlled LCD clocks show different times?
« Reply #5 on: 11/07/2009 21:12:41 »
...which of the 4 is correct ?

If my hypothesis is is correct the clock which most recently synchronised itself with the radio signal will be the closest to the true time, i.e. it will vary throughout the day which clock is the closest to the true time if they synchronise at different times.
« Last Edit: 11/07/2009 21:15:40 by RD »
 

Offline Edster

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Re: Why do radio-controlled LCD clocks show different times?
« Reply #6 on: 11/07/2009 22:06:51 »
Sorry John I edited my post when I saw it  as RD had posted before me and I was just after info, before saying anything and going into too much ruddy detail .

The GPS time signal may be the disagreeing one. ( or not)

For domestic purposes +/- 1 second is very good,

Industrial RTC receiver`s decoders  were built from logic gates and they were minimum delay. the earlist domestic ones were expensive, as it there was a medium amount of logic to do.

The decoders in most radiocode clocks are now based around a custom programmed microcontroller and it depends on the software and the cheapness factor employed in both.

If you had two identical  models then you could see  1 second difference for perhaps a 50th of second difference in  delay in decoding the heart beat last bit of the signal on sync and load.
( depending on which 2 random samples you tried)

Absolute time isn`t that easy as you go to smaller time frames, but relative time to extraordinary accuracy and confidence  is possible.  ( Ask any friendly neighbourhood Physicist/ astronomer  :) )

Any time signal you get from domestic ( or other uncompensated) sources is late. A primary national standard as used for Gps and research labs is great for frequency accuracy, but its time info  has to go down a wire, or a piece of glass fibre, and /or get transmitted.

GPS has to get its time fix from earth and rebroadcast from a distance that puts a few hundred milliseconds in the loop. Any corrections to civilian and military time signals are beyond my clearances  :)

Hope that helps without too much meander on  details I have a lot of this in paper folders from long ago, and very little I`ve googled even matches my fading memory in detail on elf/lf time signals. there was a definitive article in Elektor magazine  around 15 years ago,  now where is is my index  cd?
bests Ed





« Last Edit: 11/07/2009 22:13:20 by Edster »
 

Offline RD

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Re: Why do radio-controlled LCD clocks show different times?
« Reply #7 on: 11/07/2009 22:28:45 »

If hours pass between a particular clock synchronising its time with the radio signal then it could gain or lose a second in that period.



1 second in a day is quite fishy (IMHO)

Someone agrees with me ...
Quote
Most quartz clocks can keep time to 1 second per day or better, but some will be off by several seconds per day.
http://tf.nist.gov/timefreq/stations/radioclocks.htm
 

Offline Edster

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Re: Why do radio-controlled LCD clocks show different times?
« Reply #8 on: 11/07/2009 23:42:53 »
Now, now, calm down. less of the bolding.   :) that was not a scouse accent, honest!

it works better with the original author`s neutral stress.

I wasn`t being combative, just quoting personal experience, that can be supported by many industry source pieces of material in full without any emphasis or selectivity.
 
Around the early to mid 80`s there was a revolution in accuracy fuelled partly by certain sorts of early LCD multimeters which used a time average method for some measuremnts, this required much tighter calibration of the oscillator to get stated accuracies, this involved some of the watch firms and the cross fertilization spilled over mutually into horological modules.

 I have an LCD clock  from 1979 from an obscure manufacturer which turns out to be OEM seiko on the oscillator  bits  which still does a lot  better than a second a day, as part of a very complicated anti oversleep alarm.

 By mid 90`s you could buy a quartz  analogue hand clock which when not locked to building pulses only needed resetting every 3-4weeks  for about 50, fine you put the junior guys on on resetting them. In a broadcast environment you need a human reaction`s worth of accuracy to be on air, and that involves a verbal progressive clock check and much moaning if 1/4 wrong  from the newbies, the old pro`s  just add or subtract the seconds in their head.

A giveaway wristwatch does better than 10 seconds a month, unless it is faulty.


BIG RELEVANT QUESTION: ( oops sorry shouting)

Now who is going to buy a radio code clock? Time fanatic  or a gadget freak, or someone who really needs it for work? They seem the most likely  to me.

This will be expensive to buy as a premium object.
 
Which level of accuracy for the quartz oscillator  would you fit as a production engineer for this target market? Bearing in mind if it isn`t good enough without a synch to keep ticking over ( sorry!) to the levels of a 30 fashion wristwatch, or a freebie then wouldn`t your reputation be stuffed by the 2 sorts of people who will be very attentive to this?

I rest my case M`lud

(and  me corpse,  past pipe and slippers time).
G`night
 Ed






« Last Edit: 11/07/2009 23:48:02 by Edster »
 

Offline organmorgan

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Re: Why do radio-controlled LCD clocks show different times?
« Reply #9 on: 12/07/2009 17:04:19 »
Try again it keeps saying message box emptybut its not !
thanks for replies.
I did try comparison with GPS i have lorus watch and oregan clock in sync with GPS .
The two cheap but very clear Netto clocks are 1 sec fast.
I shall mull over what you say .Thats over a pipe ! Until
i bought the new clocks and was trying them i would never have noticed just been happy thinking the oregan scientific from argos was dead right.
cheers to all who may read John
 

Offline techmind

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Re: Why do radio-controlled LCD clocks show different times?
« Reply #10 on: 12/07/2009 20:11:18 »
The radio-controlled clocks I've come across have a "receive" button which you can press to force them to do their radio-receive "on-demand" (it takes 3-5minutes to occur from pressing the button).

You could try pressing all their collective "receive" buttons at more or less the same time, then checking the time displayed by all the clocks 5 minutes later.

I own a 1990 vintage Casio digital wristwatch (probably about £15 when I bought it in 1990 money) which gained about 20 seconds a month when I first had it. When it needed its first battery-change however, I did it myself and in the process discovered that the watch has an adjustment for time... (the outside case states "unadjusted") I tweaked this by the smallest amount I could move it with my watchmakers screwdriver... and since then it only gains about 2-3 seconds/month :)

Gaining or losing a second per day is probably not unexpected for a low-cost quartz clock. However, if the clock re-syncs daily, it should be a mere matter of software to note each day how much it gained/lost, and self-adjust (or compensate) itself. Hmmm...

You can also use the FM (absolutely not DAB) radio hourly timesignal as a check; in the UK the start of the final (long) "pip" signifies the hour.
« Last Edit: 12/07/2009 20:26:10 by techmind »
 

Offline Pumblechook

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Re: Why do radio-controlled LCD clocks show different times?
« Reply #11 on: 12/07/2009 20:15:54 »
DAB certainly introduces about a 1 -2 second delay.  FM, LW and MW introduces about a half second delay which may vary depending where you are.
 

Offline organmorgan

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Re: Why do radio-controlled LCD clocks show different times?
« Reply #12 on: 12/07/2009 20:40:44 »
Thanks Folks
its not real time i was interested in its the principle of the difference that puzzled me. I think i have some idea why now after your deliberations.
Who needs DAD in any case Will it even work in buildings and cars ?
cheers john
 

Offline techmind

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Why do radio-controlled LCD clocks show different times?
« Reply #13 on: 12/07/2009 22:23:57 »
My (operating) mobile-broadband dongle just dropped a few centimetres onto my battery powered non-radio-controlled clock... and caused the time and date to reset AND the language of the days of the week to change to French (language-change is not a documented feature for this clock).
The power of (at that moment 900MHz GSM/EDGE) radio transmissions to cause malfunction in nearby equipment  ;)

My radio-controlled clocks reset to 1am if a Vodafone phone operates (switches on / receives a text etc) within a few centimetres of them too.
« Last Edit: 16/07/2009 21:22:24 by techmind »
 

Offline organmorgan

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Why do radio-controlled LCD clocks show different times?
« Reply #14 on: 13/07/2009 17:31:23 »
well Techmind
 glad you have a sense of fun in your life.I hope you never drop off the planet could change in your absence. !

cheers fro Yorkshire
 

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Why do radio-controlled LCD clocks show different times?
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