[Elecraft] K3EXREF Query

[Brian]

Hi Alan,

Your analysis applies to the particular unit you analyzed.

In the limit of perfect insulation, the conclusion will not be true. 
The water cannot get cold when the heaters are turned off.  Thus zero 
energy required to restore the temperature.

Clearly, the insulation of the "well insulated" water heater examined 
was not perfect.

The relevant question becomes: How close to perfect insulation is the 
OCXO under discussion.  It probably isn't even close.  The case 
temperature gets hot rather quickly.  So your conclusion may apply.

73 de Brian/K3KO

P.S. This topic brings to mind an analysis of piping insulation on a 
cylindrical pipe done way back in college. Up to a point, adding more 
insulation helps.  Beyond that point, adding insulation hurts.  The 
surface area increase overwhelms the added insulation benefit.

On 10/15/2014 00:29, G4GNX wrote:
> Some years back, I was asked to do a study on the current consumption of
> a particular style of beverage vending machine. The device had a water
> tank which was well insulated and the water was heated by a 3KW heater,
> to just below boiling point. The client wanted to know whether there
> would be a saving in consumed energy, if the heater was switched off
> overnight. Careful study re4vealed that it actually cost more to heat
> the water from cold than leave the heater connected permanently,
> controlled by its thermostat.
>
> There have been numerous papers published to this effect regarding well
> insulated domestic heating systems and although there is sometimes a
> benefit in reducing the overall temperature when the building is
> unoccupied, heating from cold as opposed to leaving the heating running
> under thermostatic control, costs more, even over a short period.
>
> The oven used by a stable crystal oscillator is a thermostatically
> controlled heating device. Nuff sed! :-)
>
> 73,
>
> Alan. G4GNX
>
> -----Original Message----- From: Edward R Cole
> Sent: Tuesday, October 14, 2014 10:47 PM
> To: Elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3EXREF Query
>
> David,
>
> 10w is 7.3 kwH/month.  I would doubt that is a large expense, even in
> GB.  Locally, its about 8 cents/kwH but in the bush it might be as
> high as a couple dollars since diesel fuel for the generators costs
> are huge (local diesel is $4.10).  I know it would require conversion
> to liters and all that to come up with equivalent costs, but most
> households run hundreds of kwh/mo.  Leave your TV plugged in but
> turned off and it still consumes about 50w.  I have plug strip to
> remove ac from all my home TV systems when not in use.  I leave power
> to the satellite receiver as it keeps the LNB powered and stable
> (Otherwise it takes 5-10 minutes to acquire signal and download data
> at startup).
>
> Simple solution is to leave the reference oscillator running
> continually.  The K3 TCXO-3 will still drift on power up but this is
> compensated by EXREF every 4-seconds so frequency stability is held
> to better than 0.1 ppm.  I measured +/- 2 Hz at 28-MHz on my K3.  But
> if you watch the REF*CAL frequency you will note it incrementing from
> 49.380.000 to something like 49.380.080 in several minutes and then
> settle down near that value (indicating start-up drift has stopped).
>
> By not running your reference full time you will have to wait 15 to
> 30 minutes for it to fully warm up.  I also have a rubidium but run
> it only for precise frequency calibration of the OCXO couple times
> per year.  My mw counter internal TCXO is always in agreement with
> the Rb so I do not bother for routine frequency checks.  The rb is
> only +/- 5 E-11 so not as good as GPS but good enough for my use.
>
> 73, Ed - KL7UW
> -------------
> From: David G4DMP <david at g4dmp.fsnet.co.uk>
> To: Mike Harris <mike.harris at horizon.co.fk>
> Cc: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3EXREF Query
> Message-ID: <ulj9AOEp0TPUFwk3 at g4dmp.fsnet.co.uk>
> Content-Type: text/plain;charset=us-ascii
>
> About 10W for the MV89A double oven CXO, when run from a linear 12V
> power supply. NOT trivial at today's prices for electricity in Great
> Britain.
>
> 73 de David G4DMP
>
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