Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork

[Hal Murray]

> I'm actually speaking with one of Ed Boyden's students today who is
> interested in biosecurity!

Small world, but I'm getting used to that for things like this.

"biosecurity" gets interesting when you have probes directly into the brain.  
Do you know if the folks working on electronics to fight Parkinson's are 
paying attention to that area?


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork

[Chris Albertson]

I worked on a project once where a part was temperature sensitive.  Another
engineer, not me stuck a Peltier device on the part along with a
temperature sensor  and a crude servo using an op amp.   This was not
complex, a simple design and it held to about 1/2 degree C.Basically
made an oversized part with JB Weld epoxy and $15 in parts. Something
like that wold have put your clock spot-on.

Yes you can design very sophisticated controls and insolation and get
marginally better results at 100x cost.Did that one too.   Used water
cooling and a vacuum chamber for insulation.  That was more of a plumbing
job than an electrical job, getting the signals and water lines and vacuum
lines not to leak.

I learned to be a fan of designs that to 90% of perfect with 10% of the
cost.  On my Rb oscillator I took the cheap/easy route this time.  There is
a temperature sensor on the heat sink and a fan has its speed controlled to
keep the heatsink at constant temperature.Used just one chip to build
the fan controller an 8-pin AVR running an Arduino sketch.   The Rb is now
pretty stable

Those cheap 32K crystals might be really good if you find a low cost why to
temperature control them.  Strapping it so some one's wrist seems the best
and lowest cost way, just don't remove it.

On Tue, Apr 11, 2017 at 12:21 AM, Morris Odell 
wrote:

>
> > Most wristwatches do not have any temperature compensation. If worn, the
> wristwatch is pretty close at the 25°C (the human body is a quite good and
> temperature stable oven). The difference only starts to > show when the
> watch isn't worn for long periods of time.
>
> That explains my experience with the first microcontroller based clock I
> built years ago. I used a commercial module with a micro and some
> accessories including a watch crystal for timing. It's on a window ledge
> facing west in Australia where the temp varies during the year by 40°C. It
> was always a bit fast and I spent a lot of time checking my code to make
> sure I was dividing it by the right amount. I eventually tamed it by
> programming a short pause at 3:00 am. I'm sure the temp of the watch
> crystal is very rarely 25°C!!
>
> Morris
>
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-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork

[Morris Odell]

> Most wristwatches do not have any temperature compensation. If worn, the 
> wristwatch is pretty close at the 25°C (the human body is a quite good and 
> temperature stable oven). The difference only starts to > show when the watch 
> isn't worn for long periods of time.

That explains my experience with the first microcontroller based clock I built 
years ago. I used a commercial module with a micro and some accessories 
including a watch crystal for timing. It's on a window ledge facing west in 
Australia where the temp varies during the year by 40°C. It was always a bit 
fast and I spent a lot of time checking my code to make sure I was dividing it 
by the right amount. I eventually tamed it by programming a short pause at 3:00 
am. I'm sure the temp of the watch crystal is very rarely 25°C!!

Morris

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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Bob kb8tq]

Hi


> On Apr 9, 2017, at 10:01 PM, Alex Pummer <a...@pcscons.com> wrote:
> 
> actually it does not compensate for temperature it is just for reduce the 
> production cost for the crystal. We --Jean Hoerni [founder of intersil, 
> Eurosil and one of the  traitors who started Fairchild Semiconductor] and me 
> -- made something very similar at the time of begin of the quartz clock era 
> for Lipp a French watch maker in Bezancon [a city an France the spelling is 
> most likely not correct]. The company exhibited it at the Basler exhibition 
> of Horology, the clock was simple good working and not to expensive, Ebachos 
> --OMEGA -- people visited the booth, they also had their quartz  clock which 
> was much more expensive -- they looked, the Lipp clock and told na there are 
> Rolls-Royce s and deux chevaux [that was a simple little ugly but very 
> reliably French car ] as response Mr. Hoerni told them yes, and there are 
> technologies not known in your house, the Omega people recognized him and 
> walked away quietly...
> 
> 73
> 
> Alex

Just to put this in context. The “prior state of the art” was to have a trimmer 
capacitor in the watch (or clock) module to set it on 
frequency. That’s why it was obvious from a quick look that something was 
different. There were semiconductor companies making
watch modules at the same time still using trimmer capacitors. The pulse drop / 
add was not at all an “obvious” solution at the time. 

Bob


> 
> 
> On 4/9/2017 1:11 PM, Bill Hawkins wrote:
>> Nice article in Wikipedia. Didn't see any familiar names in the
>> reference list, though.
>> 
>> Seems to me inhibition compensation is useful for compensating for the
>> variation in purchased crystal frequencies, but not for temperature
>> compensation.
>> 
>> Also seems to me that a watch spends 2/3 of a day at wrist temperature
>> and 1/3 at bedroom temperature, which varies with the seasons.
>> 
>> Would a ceramic capacitor crafted for a certain temperature coefficient
>> work? Can the fork have a crafted tempco?
>> 
>> Bill Hawkins
>> 
>> 
>> -Original Message-
>> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Ron
>> Bean
>> Sent: Sunday, April 09, 2017 12:05 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork
>> crystal specs
>> 
>>> In your case, the car sits in an environment that matches their test
>>> setup well. In my case ?\200? not so much.
>> FWIW, mine drifts pretty badly. It's in an aftermarket stereo, and I
>> don't remember when I bought it (I moved it from my previous car).
>> 
>> I assume that all quartz clocks and watches these days use "inhibition
>> conpensation".
>> 
>> https://en.wikipedia.org/wiki/Quartz_clock#Inhibition_compensation
>> 
>> 
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>> 
>> 
>> -
>> No virus found in this message.
>> Checked by AVG - www.avg.com
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> 
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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Bob kb8tq]

Hi

The compensation process either for a clock or a watch has been embedded
in the IC for a lot of years now. They do a pulse add / pulse drop approach 
to “level out” the 1 pps drive to the display. Temperature does not move fast
enough that averaging things over a minute is an issue. That gives them < 
1 ppm resolution which is better than what they know about temperature. It
is also good enough to set it on “at the factory” to run at whatever rate they
decide on. In most cases the nominal target is for the watch or car clock to 
run a bit fast (= it’s never slow) rather than try to set it dead on. Most 
people 
yell at watches when they are late ….

Bob

> On Apr 9, 2017, at 4:11 PM, Bill Hawkins <bill.i...@pobox.com> wrote:
> 
> Nice article in Wikipedia. Didn't see any familiar names in the
> reference list, though.
> 
> Seems to me inhibition compensation is useful for compensating for the
> variation in purchased crystal frequencies, but not for temperature
> compensation.
> 
> Also seems to me that a watch spends 2/3 of a day at wrist temperature
> and 1/3 at bedroom temperature, which varies with the seasons.
> 
> Would a ceramic capacitor crafted for a certain temperature coefficient
> work? Can the fork have a crafted tempco?
> 
> Bill Hawkins
> 
> 
> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Ron
> Bean
> Sent: Sunday, April 09, 2017 12:05 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork
> crystal specs
> 
>> In your case, the car sits in an environment that matches their test 
>> setup well. In my case ?\200? not so much.
> 
> FWIW, mine drifts pretty badly. It's in an aftermarket stereo, and I
> don't remember when I bought it (I moved it from my previous car).
> 
> I assume that all quartz clocks and watches these days use "inhibition
> conpensation".
> 
> https://en.wikipedia.org/wiki/Quartz_clock#Inhibition_compensation
> 
> 
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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Alex Pummer]

actually it does not compensate for temperature it is just for reduce 
the production cost for the crystal. We --Jean Hoerni [founder of 
intersil, Eurosil and one of the  traitors who started Fairchild 
Semiconductor] and me -- made something very similar at the time of 
begin of the quartz clock era for Lipp a French watch maker in Bezancon 
[a city an France the spelling is most likely not correct]. The company 
exhibited it at the Basler exhibition of Horology, the clock was simple 
good working and not to expensive, Ebachos --OMEGA -- people visited the 
booth, they also had their quartz  clock which was much more expensive 
-- they looked, the Lipp clock and told na there are Rolls-Royce s and 
deux chevaux [that was a simple little ugly but very reliably French car 
] as response Mr. Hoerni told them yes, and there are technologies not 
known in your house, the Omega people recognized him and walked away 
quietly...


73

Alex


On 4/9/2017 1:11 PM, Bill Hawkins wrote:

Nice article in Wikipedia. Didn't see any familiar names in the
reference list, though.

Seems to me inhibition compensation is useful for compensating for the
variation in purchased crystal frequencies, but not for temperature
compensation.

Also seems to me that a watch spends 2/3 of a day at wrist temperature
and 1/3 at bedroom temperature, which varies with the seasons.

Would a ceramic capacitor crafted for a certain temperature coefficient
work? Can the fork have a crafted tempco?

Bill Hawkins


-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Ron
Bean
Sent: Sunday, April 09, 2017 12:05 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork
crystal specs


In your case, the car sits in an environment that matches their test
setup well. In my case ?\200? not so much.

FWIW, mine drifts pretty badly. It's in an aftermarket stereo, and I
don't remember when I bought it (I moved it from my previous car).

I assume that all quartz clocks and watches these days use "inhibition
conpensation".

https://en.wikipedia.org/wiki/Quartz_clock#Inhibition_compensation


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-
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2016.0.8012 / Virus Database: 4769/14275 - Release Date: 04/09/17


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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Bill Hawkins]

Nice article in Wikipedia. Didn't see any familiar names in the
reference list, though.

Seems to me inhibition compensation is useful for compensating for the
variation in purchased crystal frequencies, but not for temperature
compensation.

Also seems to me that a watch spends 2/3 of a day at wrist temperature
and 1/3 at bedroom temperature, which varies with the seasons.

Would a ceramic capacitor crafted for a certain temperature coefficient
work? Can the fork have a crafted tempco?

Bill Hawkins


-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Ron
Bean
Sent: Sunday, April 09, 2017 12:05 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork
crystal specs

>In your case, the car sits in an environment that matches their test 
>setup well. In my case ?\200? not so much.

FWIW, mine drifts pretty badly. It's in an aftermarket stereo, and I
don't remember when I bought it (I moved it from my previous car).

I assume that all quartz clocks and watches these days use "inhibition
conpensation".

https://en.wikipedia.org/wiki/Quartz_clock#Inhibition_compensation


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[time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Mark Sims]

My 30 year old Mercedes has an analog clock in it.  I've always been amazed how 
well it keeps time.  A couple of years ago, I set it for daylight savings time 
in the spring and did not reset it in the winter.  Next spring it was still 
accurate to within the resolution of reading the hands.   I was going to let it 
run for another year, but the car battery needed to be replaced that summer.

I don't know how they implemented the clock,  but whatever they did works damn 
well.  In the summer around here a car interior can get to over 140F if left in 
the sun (with obligatory news segments of people cooking eggs and cookies in 
their cars).  The clock has never been serviced in 30 years and is still 
ticking like new.
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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Brooke Clarke]

Hi Ron:

I think HP pioneered that method in one of their hand held calculators (PH35 or 
PH41)?

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

 Original Message 

In your case, the car sits in an environment that matches their test
setup well. In my case �\200� not so much.

FWIW, mine drifts pretty badly. It's in an aftermarket stereo, and I
don't remember when I bought it (I moved it from my previous car).

I assume that all quartz clocks and watches these days use "inhibition
conpensation".

https://en.wikipedia.org/wiki/Quartz_clock#Inhibition_compensation




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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Tim Shoppa]

Interesting that someone would complain their car clock, kept at
temperature controlled 25C, runs fast.

The manufacturer would set the clock calibration, not at 25C, but at 10C
(typical winter temperature) or 40C (average of cool night and baking hot
car interior temperature in summer).

So one half of the year the average temperature is on one side of the 25C
crystal turning point hump.

And the other half of the year the average temperature is on the other side
of the 25C crystal turning point hump.

Someone who put the clock indoors, at a fixed 25C temperature, would indeed
see the clock running fast.

But someone who keeps it in the changing outdoor weather, might find it
running on time (on average) in both winter half and summer half of year.

Still impressive that it's better than 4ppm on average over summer and
winter.

Tim N3QE

On Sun, Apr 9, 2017 at 7:45 AM, Tim Shoppa  wrote:

> I've had only a few different cars over the past 25 years but I've been
> impressed with how accurate their mass-market built-in clocks are,
> especially considering the wide and completely uncontrolled temperature
> range. In the winter the interior of the car gets down below freezing most
> mornings, and in the summer the interior gets way above 120F in sunlight.
>
> (Contrast the above with the time-nuttery here where folks buy double-oven
> OCXO's and then they insist that the OCXO's have to be put in temperature
> controlled environments.)
>
> I only set the car clock twice a year, at daylight savings time changes.
> Yet between daylight savings time changes, the car clock never drifts by
> more than a minute.
>
> 60 seconds in half a year is 4ppm. So I went and looked at the specs of a
> stock 32kHz crystal, for example http://www.mouser.com/
> ds/2/77/CFS-CFV-4402.pdf
>
> 1: The crystal is speced as having a turnover point of 25C. I understand
> that.
> 2: Frequency at the turnover point is speced as being +/-20ppm. OK, that's
> not bad, most of that can be compensated for with a small trimmer cap at
> the factory to the 4ppm range. Or maybe they just program in the clock
> divider at the factory appropriate to the crystal.
> 3: The temperature coefficient of the tuning fork cut around the turnover
> point seems to always be the same: -.034ppm per deg C squared. If the temp
> goes down to 5 deg C, then, the frequency changes by 14ppm. If the temp
> goes down to -5 deg C, the frequency changes by 30ppm.
>
> With that temperature coefficient, temperatures like -5C or 5C that are
> common every winter would result in a few minutes of drift every winter.
> Yet I never observe that drift.
>
> So my conclusion, is that all these car clocks must be temperature
> compensated. And they must've been doing this for several decades at this
> point.
>
> That shouldn't be too surprising - right next to the clock display on the
> dashboard is a digital thermometer. Maybe 30 or more years ago the
> temperature compensation was done by analog circuitry, but today I'm
> guessing there's a digital chip that takes the thermometer reading and
> numerically adjusts the divider word for the 32kHz oscillator to
> temperature compensate the clock digitally.
>
> Is there a way to verify my guess at the TCXO method?
>
> I'm guessing that all the better quartz wristwatches use a similar
> technology too. Maybe they have a different crystal cut that is closer to
> body temperature for the turnover point.
>
> Tim N3QE
>
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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Bob kb8tq]

Hi



> On Apr 9, 2017, at 11:36 AM, Clint Jay  wrote:
> 
> The clocks in my car have been set by the RDS data, DAB data or GPS in the
> last five or six I've had. Drift is a thing of the past as long as i listen
> to digital radio or the BBC on analogue FM, if i listen to neither then the
> clock drifts a couple of seconds a month but it syncs right up withing a
> minute or two of DAB or BBC FM.
> 
> The GPS set clocks never noticeably change.
> 
> I have a vague memory of at least one of the crystal controlled clocks
> having a 4.194304MHz crystal which, i think, so a divide by 2^22 if memory
> serves which would make for lower drift in the 1HZ?

The advantage of the 4 MHz frequency is that it gets you in range for an AT cut 
crystal. That gives you a third order temperature coefficient rather than the 
parabola 
you get with the various bar cuts at 32 KHz. For a modest amount of money you
*could* cut an AT so it will hold 5 ppm over the 0 to 50C range (sort of but 
not really
0.5 ppm/ C) . That compares to the 20 ppm / C previously quoted for the 32 KHz 
parts (which is also a “sort of” number since the parabola gets steeper as you 
get further from the inflection) 

Bob

> 
> On 9 Apr 2017 2:01 pm, "Tim Shoppa"  wrote:
> 
>> I've had only a few different cars over the past 25 years but I've been
>> impressed with how accurate their mass-market built-in clocks are,
>> especially considering the wide and completely uncontrolled temperature
>> range. In the winter the interior of the car gets down below freezing most
>> mornings, and in the summer the interior gets way above 120F in sunlight.
>> 
>> (Contrast the above with the time-nuttery here where folks buy double-oven
>> OCXO's and then they insist that the OCXO's have to be put in temperature
>> controlled environments.)
>> 
>> I only set the car clock twice a year, at daylight savings time changes.
>> Yet between daylight savings time changes, the car clock never drifts by
>> more than a minute.
>> 
>> 60 seconds in half a year is 4ppm. So I went and looked at the specs of a
>> stock 32kHz crystal, for example
>> http://www.mouser.com/ds/2/77/CFS-CFV-4402.pdf
>> 
>> 1: The crystal is speced as having a turnover point of 25C. I understand
>> that.
>> 2: Frequency at the turnover point is speced as being +/-20ppm. OK, that's
>> not bad, most of that can be compensated for with a small trimmer cap at
>> the factory to the 4ppm range. Or maybe they just program in the clock
>> divider at the factory appropriate to the crystal.
>> 3: The temperature coefficient of the tuning fork cut around the turnover
>> point seems to always be the same: -.034ppm per deg C squared. If the temp
>> goes down to 5 deg C, then, the frequency changes by 14ppm. If the temp
>> goes down to -5 deg C, the frequency changes by 30ppm.
>> 
>> With that temperature coefficient, temperatures like -5C or 5C that are
>> common every winter would result in a few minutes of drift every winter.
>> Yet I never observe that drift.
>> 
>> So my conclusion, is that all these car clocks must be temperature
>> compensated. And they must've been doing this for several decades at this
>> point.
>> 
>> That shouldn't be too surprising - right next to the clock display on the
>> dashboard is a digital thermometer. Maybe 30 or more years ago the
>> temperature compensation was done by analog circuitry, but today I'm
>> guessing there's a digital chip that takes the thermometer reading and
>> numerically adjusts the divider word for the 32kHz oscillator to
>> temperature compensate the clock digitally.
>> 
>> Is there a way to verify my guess at the TCXO method?
>> 
>> I'm guessing that all the better quartz wristwatches use a similar
>> technology too. Maybe they have a different crystal cut that is closer to
>> body temperature for the turnover point.
>> 
>> Tim N3QE
>> ___
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>> 
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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Clint Jay]

The clocks in my car have been set by the RDS data, DAB data or GPS in the
last five or six I've had. Drift is a thing of the past as long as i listen
to digital radio or the BBC on analogue FM, if i listen to neither then the
clock drifts a couple of seconds a month but it syncs right up withing a
minute or two of DAB or BBC FM.

The GPS set clocks never noticeably change.

I have a vague memory of at least one of the crystal controlled clocks
having a 4.194304MHz crystal which, i think, so a divide by 2^22 if memory
serves which would make for lower drift in the 1HZ?

On 9 Apr 2017 2:01 pm, "Tim Shoppa"  wrote:

> I've had only a few different cars over the past 25 years but I've been
> impressed with how accurate their mass-market built-in clocks are,
> especially considering the wide and completely uncontrolled temperature
> range. In the winter the interior of the car gets down below freezing most
> mornings, and in the summer the interior gets way above 120F in sunlight.
>
> (Contrast the above with the time-nuttery here where folks buy double-oven
> OCXO's and then they insist that the OCXO's have to be put in temperature
> controlled environments.)
>
> I only set the car clock twice a year, at daylight savings time changes.
> Yet between daylight savings time changes, the car clock never drifts by
> more than a minute.
>
> 60 seconds in half a year is 4ppm. So I went and looked at the specs of a
> stock 32kHz crystal, for example
> http://www.mouser.com/ds/2/77/CFS-CFV-4402.pdf
>
> 1: The crystal is speced as having a turnover point of 25C. I understand
> that.
> 2: Frequency at the turnover point is speced as being +/-20ppm. OK, that's
> not bad, most of that can be compensated for with a small trimmer cap at
> the factory to the 4ppm range. Or maybe they just program in the clock
> divider at the factory appropriate to the crystal.
> 3: The temperature coefficient of the tuning fork cut around the turnover
> point seems to always be the same: -.034ppm per deg C squared. If the temp
> goes down to 5 deg C, then, the frequency changes by 14ppm. If the temp
> goes down to -5 deg C, the frequency changes by 30ppm.
>
> With that temperature coefficient, temperatures like -5C or 5C that are
> common every winter would result in a few minutes of drift every winter.
> Yet I never observe that drift.
>
> So my conclusion, is that all these car clocks must be temperature
> compensated. And they must've been doing this for several decades at this
> point.
>
> That shouldn't be too surprising - right next to the clock display on the
> dashboard is a digital thermometer. Maybe 30 or more years ago the
> temperature compensation was done by analog circuitry, but today I'm
> guessing there's a digital chip that takes the thermometer reading and
> numerically adjusts the divider word for the 32kHz oscillator to
> temperature compensate the clock digitally.
>
> Is there a way to verify my guess at the TCXO method?
>
> I'm guessing that all the better quartz wristwatches use a similar
> technology too. Maybe they have a different crystal cut that is closer to
> body temperature for the turnover point.
>
> Tim N3QE
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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Ron Bean]

>In your case, the car sits in an environment that matches their test 
>setup well. In my case �\200� not so much.

FWIW, mine drifts pretty badly. It's in an aftermarket stereo, and I 
don't remember when I bought it (I moved it from my previous car).

I assume that all quartz clocks and watches these days use "inhibition 
conpensation".

https://en.wikipedia.org/wiki/Quartz_clock#Inhibition_compensation




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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Chris Albertson]

On Sun, Apr 9, 2017 at 4:45 AM, Tim Shoppa  wrote:
> I've had only a few different cars over the past 25 years but I've been
> impressed with how accurate their mass-market built-in clocks are,

Have you always lived in the same place.  What is the average year
round temperature there?

What I live the clocks always gain time, a minute every could mounts.
It seems I always have to set the time back a minute or two.  But then
it really never gets cold here, maybe a dip below 50F at night in the
winter



-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Scott Stobbe]

The trim method that stands out from memory for generic RTC chips is to
cycle stall or double clock, x cycles every 60 seconds. Yielding 0.5 ppm
trim resolution.

On Sun, Apr 9, 2017 at 7:45 AM, Tim Shoppa  wrote:

> I've had only a few different cars over the past 25 years but I've been
> impressed with how accurate their mass-market built-in clocks are,
> especially considering the wide and completely uncontrolled temperature
> range. In the winter the interior of the car gets down below freezing most
> mornings, and in the summer the interior gets way above 120F in sunlight.
>
> (Contrast the above with the time-nuttery here where folks buy double-oven
> OCXO's and then they insist that the OCXO's have to be put in temperature
> controlled environments.)
>
> I only set the car clock twice a year, at daylight savings time changes.
> Yet between daylight savings time changes, the car clock never drifts by
> more than a minute.
>
> 60 seconds in half a year is 4ppm. So I went and looked at the specs of a
> stock 32kHz crystal, for example
> http://www.mouser.com/ds/2/77/CFS-CFV-4402.pdf
>
> 1: The crystal is speced as having a turnover point of 25C. I understand
> that.
> 2: Frequency at the turnover point is speced as being +/-20ppm. OK, that's
> not bad, most of that can be compensated for with a small trimmer cap at
> the factory to the 4ppm range. Or maybe they just program in the clock
> divider at the factory appropriate to the crystal.
> 3: The temperature coefficient of the tuning fork cut around the turnover
> point seems to always be the same: -.034ppm per deg C squared. If the temp
> goes down to 5 deg C, then, the frequency changes by 14ppm. If the temp
> goes down to -5 deg C, the frequency changes by 30ppm.
>
> With that temperature coefficient, temperatures like -5C or 5C that are
> common every winter would result in a few minutes of drift every winter.
> Yet I never observe that drift.
>
> So my conclusion, is that all these car clocks must be temperature
> compensated. And they must've been doing this for several decades at this
> point.
>
> That shouldn't be too surprising - right next to the clock display on the
> dashboard is a digital thermometer. Maybe 30 or more years ago the
> temperature compensation was done by analog circuitry, but today I'm
> guessing there's a digital chip that takes the thermometer reading and
> numerically adjusts the divider word for the 32kHz oscillator to
> temperature compensate the clock digitally.
>
> Is there a way to verify my guess at the TCXO method?
>
> I'm guessing that all the better quartz wristwatches use a similar
> technology too. Maybe they have a different crystal cut that is closer to
> body temperature for the turnover point.
>
> Tim N3QE
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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[William H. Fite]

Good quartz watches are, indeed, temperature compensated. More info here:
http://forums.watchuseek.com/f9/thermocompensation-methods-movements-2087.html#/topics/2087?page=1

Of much greater interest to watch nerds like me is the improvement of
accuracy in mechanical watch movements. Serious watch enthusiasts don't
spend (many would say waste) a lot of time on quartz technology.

Mechanical horology is a corner of time nuttery all to itself.

Bill



On Sunday, April 9, 2017, Tim Shoppa  wrote:

> I've had only a few different cars over the past 25 years but I've been
> impressed with how accurate their mass-market built-in clocks are,
> especially considering the wide and completely uncontrolled temperature
> range. In the winter the interior of the car gets down below freezing most
> mornings, and in the summer the interior gets way above 120F in sunlight.
>
> (Contrast the above with the time-nuttery here where folks buy double-oven
> OCXO's and then they insist that the OCXO's have to be put in temperature
> controlled environments.)
>
> I only set the car clock twice a year, at daylight savings time changes.
> Yet between daylight savings time changes, the car clock never drifts by
> more than a minute.
>
> 60 seconds in half a year is 4ppm. So I went and looked at the specs of a
> stock 32kHz crystal, for example
> http://www.mouser.com/ds/2/77/CFS-CFV-4402.pdf
>
> 1: The crystal is speced as having a turnover point of 25C. I understand
> that.
> 2: Frequency at the turnover point is speced as being +/-20ppm. OK, that's
> not bad, most of that can be compensated for with a small trimmer cap at
> the factory to the 4ppm range. Or maybe they just program in the clock
> divider at the factory appropriate to the crystal.
> 3: The temperature coefficient of the tuning fork cut around the turnover
> point seems to always be the same: -.034ppm per deg C squared. If the temp
> goes down to 5 deg C, then, the frequency changes by 14ppm. If the temp
> goes down to -5 deg C, the frequency changes by 30ppm.
>
> With that temperature coefficient, temperatures like -5C or 5C that are
> common every winter would result in a few minutes of drift every winter.
> Yet I never observe that drift.
>
> So my conclusion, is that all these car clocks must be temperature
> compensated. And they must've been doing this for several decades at this
> point.
>
> That shouldn't be too surprising - right next to the clock display on the
> dashboard is a digital thermometer. Maybe 30 or more years ago the
> temperature compensation was done by analog circuitry, but today I'm
> guessing there's a digital chip that takes the thermometer reading and
> numerically adjusts the divider word for the 32kHz oscillator to
> temperature compensate the clock digitally.
>
> Is there a way to verify my guess at the TCXO method?
>
> I'm guessing that all the better quartz wristwatches use a similar
> technology too. Maybe they have a different crystal cut that is closer to
> body temperature for the turnover point.
>
> Tim N3QE
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> To unsubscribe, go to https://www.febo.com/cgi-bin/
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> and follow the instructions there.
>


-- 
William H Fite, PhD
Independent Consultant
Statistical Analysis & Research Methods
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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Bob kb8tq]

Hi

In my “test environment” car clocks always run fast. That’s been true for many
decades over many manufacturers. 

The idea of putting in an offset on a timekeeping device is an old one. You run 
the
beast over the “expected” temperature (and other environmental) range. You
observe how fast or slow it is and adjust it. To the extent your test model 
matches
the real world, the clock runs fine or not so fine. 

In your case, the car sits in an environment that matches their test setup 
well. In my
case … not so much. 

Indeed a modern watch / clock likely does some basic temperature compensation. 
The 
gotcha is that the crystals are all over the place. The “25 C” inflection 
temperature is 
anything from 15 to 35C (or more). The 20 ppm slope is anything from 10 to 30 
(or more).
They can’t afford to run the parts over temperature (as you would with a TCXO) 
so 
you get a “nominal” compensation at best. 

Bob

> On Apr 9, 2017, at 7:45 AM, Tim Shoppa  wrote:
> 
> I've had only a few different cars over the past 25 years but I've been
> impressed with how accurate their mass-market built-in clocks are,
> especially considering the wide and completely uncontrolled temperature
> range. In the winter the interior of the car gets down below freezing most
> mornings, and in the summer the interior gets way above 120F in sunlight.
> 
> (Contrast the above with the time-nuttery here where folks buy double-oven
> OCXO's and then they insist that the OCXO's have to be put in temperature
> controlled environments.)
> 
> I only set the car clock twice a year, at daylight savings time changes.
> Yet between daylight savings time changes, the car clock never drifts by
> more than a minute.
> 
> 60 seconds in half a year is 4ppm. So I went and looked at the specs of a
> stock 32kHz crystal, for example
> http://www.mouser.com/ds/2/77/CFS-CFV-4402.pdf
> 
> 1: The crystal is speced as having a turnover point of 25C. I understand
> that.
> 2: Frequency at the turnover point is speced as being +/-20ppm. OK, that's
> not bad, most of that can be compensated for with a small trimmer cap at
> the factory to the 4ppm range. Or maybe they just program in the clock
> divider at the factory appropriate to the crystal.
> 3: The temperature coefficient of the tuning fork cut around the turnover
> point seems to always be the same: -.034ppm per deg C squared. If the temp
> goes down to 5 deg C, then, the frequency changes by 14ppm. If the temp
> goes down to -5 deg C, the frequency changes by 30ppm.
> 
> With that temperature coefficient, temperatures like -5C or 5C that are
> common every winter would result in a few minutes of drift every winter.
> Yet I never observe that drift.
> 
> So my conclusion, is that all these car clocks must be temperature
> compensated. And they must've been doing this for several decades at this
> point.
> 
> That shouldn't be too surprising - right next to the clock display on the
> dashboard is a digital thermometer. Maybe 30 or more years ago the
> temperature compensation was done by analog circuitry, but today I'm
> guessing there's a digital chip that takes the thermometer reading and
> numerically adjusts the divider word for the 32kHz oscillator to
> temperature compensate the clock digitally.
> 
> Is there a way to verify my guess at the TCXO method?
> 
> I'm guessing that all the better quartz wristwatches use a similar
> technology too. Maybe they have a different crystal cut that is closer to
> body temperature for the turnover point.
> 
> Tim N3QE
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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Attila Kinali]

On Sun, 9 Apr 2017 07:45:23 -0400
Tim Shoppa  wrote:

> So my conclusion, is that all these car clocks must be temperature
> compensated. And they must've been doing this for several decades at this
> point.

Yes, definitely. Although in the 80s it was only the higher class cars.

> That shouldn't be too surprising - right next to the clock display on the
> dashboard is a digital thermometer. Maybe 30 or more years ago the
> temperature compensation was done by analog circuitry, but today I'm
> guessing there's a digital chip that takes the thermometer reading and
> numerically adjusts the divider word for the 32kHz oscillator to
> temperature compensate the clock digitally.

I'd rather guess that it is some RTC package with crystal, temp sensor
and battery in single package, and they use the internal temp sensor
of the RTC for the dashboard display.
 
> Is there a way to verify my guess at the TCXO method?

Beside opening up the dashboard and looking for the RTC or placing
the car in a climate chamber and measuring the temperature coefficient?
I don't think so.
 
> I'm guessing that all the better quartz wristwatches use a similar
> technology too. Maybe they have a different crystal cut that is closer to
> body temperature for the turnover point.

Most wristwatches do not have any temperature compensation. If worn, the
wristwatch is pretty close at the 25°C (the human body is a quite good
and temperature stable oven). The difference only starts to show when
the watch isn't worn for long periods of time.


Attila Kinali
-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[iovane--- via time-nuts]

>I only set the car clock twice a year, at daylight savings time changes.
>Yet between daylight savings time changes, the car clock never drifts by
>more than a minute.

Just to testify that I do exactly the same on the clock of my old mercedes. I' 
ve alwais been unable to estimate the half-year drift because it is always very 
less than 1 minute.

iov
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[time-nuts] Car Clock drift - the lowly 32kHz tuning fork crystal specs

[Tim Shoppa]

I've had only a few different cars over the past 25 years but I've been
impressed with how accurate their mass-market built-in clocks are,
especially considering the wide and completely uncontrolled temperature
range. In the winter the interior of the car gets down below freezing most
mornings, and in the summer the interior gets way above 120F in sunlight.

(Contrast the above with the time-nuttery here where folks buy double-oven
OCXO's and then they insist that the OCXO's have to be put in temperature
controlled environments.)

I only set the car clock twice a year, at daylight savings time changes.
Yet between daylight savings time changes, the car clock never drifts by
more than a minute.

60 seconds in half a year is 4ppm. So I went and looked at the specs of a
stock 32kHz crystal, for example
http://www.mouser.com/ds/2/77/CFS-CFV-4402.pdf

1: The crystal is speced as having a turnover point of 25C. I understand
that.
2: Frequency at the turnover point is speced as being +/-20ppm. OK, that's
not bad, most of that can be compensated for with a small trimmer cap at
the factory to the 4ppm range. Or maybe they just program in the clock
divider at the factory appropriate to the crystal.
3: The temperature coefficient of the tuning fork cut around the turnover
point seems to always be the same: -.034ppm per deg C squared. If the temp
goes down to 5 deg C, then, the frequency changes by 14ppm. If the temp
goes down to -5 deg C, the frequency changes by 30ppm.

With that temperature coefficient, temperatures like -5C or 5C that are
common every winter would result in a few minutes of drift every winter.
Yet I never observe that drift.

So my conclusion, is that all these car clocks must be temperature
compensated. And they must've been doing this for several decades at this
point.

That shouldn't be too surprising - right next to the clock display on the
dashboard is a digital thermometer. Maybe 30 or more years ago the
temperature compensation was done by analog circuitry, but today I'm
guessing there's a digital chip that takes the thermometer reading and
numerically adjusts the divider word for the 32kHz oscillator to
temperature compensate the clock digitally.

Is there a way to verify my guess at the TCXO method?

I'm guessing that all the better quartz wristwatches use a similar
technology too. Maybe they have a different crystal cut that is closer to
body temperature for the turnover point.

Tim N3QE
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