Why are my electronic clocks slow?

[Payin-the-Toll]

I have a 6-yr old 31" GE regular TV with remote and the internal clock on it loses 2-3 minutes a month. My year old combo DVD/recorder/player/VCR has an internal clock that just started losing 3-4 minutes a month. My 7-yr old refubished computer has an internal clock that loses 1-2 minutes a month. This is not due to power outages and the units are on basically 24/7. I understand a wind up clock getting tired springs/etc. and going slow, but why and how do these electronic controlled clocks lose time?

 

[DRiP Guy]

My best guess is if you may be 'missing cycles' (i.e. your AC is supposed to be 60HZ in US) -- do you know what your type of power generation is?

 

[cute fuzzy bunny]

Clock drift
http://en.wikipedia.org/wiki/Clock_drift

Every electronic clock is "off" by a little bit. Many get worse over time.

There are a bazoodle of add on software products that will set your computers time to an online atomic clock. XP has this functionality built in.

By the way, the clock drift on a PC is so predictable that someone who records a series of Internet Protocol transactions over time can identify from the time stamps on the packets both the offset and frequency of the drift on the sending PC. If the sending PC is then obtained, these can be matched up like fingerprints to demonstrate that the particular computer is the one that sent the IP packets.

Interesting stuff...

 

[Nords]

By the way, the clock drift on a PC is so predictable that someone who records a series of Internet Protocol transactions over time can identify from the time stamps on the packets both the offset and frequency of the drift on the sending PC. If the sending PC is then obtained, these can be matched up like fingerprints to demonstrate that the particular computer is the one that sent the IP packets.

So now do you not only have to use proxy servers, you have to access them by randomly switching among household PCs, and reset their clocks every day!

 

[cute fuzzy bunny]

Actually its not the time setting, but the measurable drift, so you cant fake it out.

http://www.caida.org/publications/p.../KohnoBroidoClaffy05-devicefingerprinting.pdf

In a nutshell, by analyzing two sets of packet traces you can determine with some reasonable certainty whether they came from the same machine or not, providing the traces were taken within a reasonable time of each other as the clock drift changes over time.

You have to really love measurable and predictable wrongness.

 

[Donzo]

ALL of my clocks, electronic, quartz and wind up need to be adjusted - the only clock I trust is an "atomic" clock that came w/ my wireless weather system. It is updated from the "heavens" daily - also keeps track of moon cycles, date etc.---since retiring I often need help remembering the day and date - also if we are going to have a get together, I like to have it around a full moon(esp. summer) and this thing makes it easy.

 

[Telly]

I have a 6-yr old 31" GE regular TV with remote and the internal clock on it loses 2-3 minutes a month. My year old combo DVD/recorder/player/VCR has an internal clock that just started losing 3-4 minutes a month. My 7-yr old refubished computer has an internal clock that loses 1-2 minutes a month. This is not due to power outages and the units are on basically 24/7. I understand a wind up clock getting tired springs/etc. and going slow, but why and how do these electronic controlled clocks lose time?

All of those devices use a consumer-grade crystal oscillator in them for the timebase. The crystals used are dirt cheap. The cutting and lapping of crystals create stresses in the lattice. Much more expensive Industrial-grade crystals are baked to help relieve these stresses before the final manufacturing operations. You get what you (don't) pay for.

In addition, any change in series or parallel capacitance in the oscillator circuitry will pull the crystal frequency. This is both bad and good. Good, in that a small trimmer capacitor could be adjusted by the user (a Fast - Slow screwdriver adjustment) to correct a slightly off-frequency crystal. And bad, in that any aging of cheap components in the circuit could have the same effect.

For your VCR, check the instructions. Most VCR's have an automatic clock set mode, which will use a time signal sent by a TV station to synchronize the internal VCR clock. Your VCR probably has a learn mode that will scan through all available channels, and mark one that it see's a time signal on. It will then use that for the synch reference. In my case, it was a PBS TV station that had it. When your VCR is "off"it will continue to run on your internal VCR clock. When the VCR is back on, it will look at the time signal and resynch the internal clock.

 

[ERD50]

Yep, Telly has it right.

Another way to look at it, is just how accurate 4 minutes in a month really is (glass half full).

4 minutes divided by the minutes in a month (60min * 24 hrs * 30 days) = 93 millionths.

Or 93 ppm accuracy.

Or 99.9907% accurate.

Or .0093% inaccuracy.

Amazing just how good a dirt-cheap device is. Try to buy a torque wrench, or a tire pressure gauge, or a meat thermometer, or a bathroom scale that is 99.9907% accurate! That would weigh a 175 pound person to within about 1/4 of an ounce!

They could design in a better part, but it would still be off a minute every month or two. So, if you care, you would still be adjusting it. To get much better, you really need to get to some pretty fancy and somewhat costly circuits; temperature and voltage compensation, maybe a little computer chip to track all the non-linearities. It just isn't worth it for most products, esp when most people change the time twice a year anyhow. And, as stated above, there are options if you really want/need the accuracy.

I'd rather see them spend (and charge) a few more bucks to make sure the clock does not lose it's settings on every little power glitch. That is infuriating to me, yet, you can rarely find out from the product literature if it has that feature or not.

-ERD50