[time-nuts] Fwd: Fwd: HP5061B Versus HP5071 Cesium Line Frequencies

[Donald E. Pauly]

https://www.febo.com/pipermail/time-nuts/2017-June/date.html

I am familiar with this effect.  My specialty is switching amplifiers
and I wrote the classic paper for Motorola on the subject, see
http://gonascent.com/papers/an1042.pdf .  Ripple in the dc from a
switching amplifier is less than a part per thousand.  These thermal
coolers have about a 10% efficiency which means it takes 10 Watts to
pump a Watt.  That is a tiny switching amplifier.  Ovens also require
several Watts if operated at -55° C.  Thermo coolers/heaters require
little power when operated close to room temperature.  Highest power
is required at high ambient temperatures.

πθ°μΩω±√·Γ
WB0KVV
https://www.febo.com/pipermail/time-nuts/2017-June/date.html
---------- Forwarded message ----------
From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Date: Fri, Jun 2, 2017 at 4:34 PM
Subject: Re: [time-nuts] Fwd: HP5061B Versus HP5071 Cesium Line Frequencies
To: jimlux <jimlux at earthlink.net>, Discussion of precise time and
frequency measurement <time-nuts at febo.com>


Thermomechanical fatigue can significantly reduce the lifetime of
Peltier devices if the ripple current flowing in the Peltier device is
too high. This can become an issue with switchmode drive to a Peltier
cooler.

Bruce


>
>     On 03 June 2017 at 11:02 jimlux <jimlux at earthlink.net> wrote:
>
>     On 6/2/17 2:51 PM, Donald E. Pauly wrote:
>
>         > >
> >         This is an improvement of 476 to 1. You apparently have not thought
> >         thru what improvements are possible with thermal coolers/heaters.
> >         Among these is near instant warm up and greatly reduced power for
> >         thermal management.
> >
> >     >
>     without getting into the whole crystal issue, one of the advantages of a
>     heater is that it can be VERY simple (and hence reliable, just on a
>     parts count basis). With a decent package, once it's hot, the power
>     required to keep it hot can be quite low.
>
>     With a heat/cool, you need to be able to have a bipolar supply to the
>     peltier device, and they're not particularly efficient (that is, to
>     extract 1 Watt of heat, you're putting in significantly more than 1 watt
>     of DC, and rejecting 1+X watts to the outside world.
>
>     And then, if you use a linear power supply/amplifier to drive the
>     device, that is probably a class A device, and somewhat lossy. A
>     switcher would be more efficient, but then you have the problem of
>     switching noise, in close proximity to the crystal. You could put a big
>     low pass filter in, but now you're adding even more components.
>
>     There are undoubtedly some cases where the thermoelectric scheme would
>     work better - for instance, you have a system with a TCXO and it's
>     really set up for the TCXO to be at 25C, and you want to regulate that.
>
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