[time-nuts] SMPS or conventional?

[Neville Michie]

IN the Datum User’s Guide for the LPRO there is a set of data for MTBF.
Ambient Temperature    MTBF Hours
20 			381000
25			351000
30			320000
40			253000
50			189000
60			134000
This shows the clear advantage of keeping to unit cool.
The data also shows the improved stability if the temperature is constant.

cheers, Neville Michie




> On 21 Oct 2020, at 23:40, Wannes Sels <wannes.sels at gmail.com> wrote:
> 
> There are conflicting requirements regarding temperature in Rb's:
> 
> - For best performance, the rubidium and quartz oscillators must be kept at
> a high and stable temperature.
> - For reliability, the supporting electronics must be kept at a lower
> temperature.
> 
> The heater takes care of the high temperature. The stability of the
> temperature can be improved by increasing the thermal mass, i.e. adding a
> block of aluminium or copper.
> The electronics can be kept cooler with a heatsink, and forced ventilation
> if needed.
> 
> When you stick both the electronics and physics in a small package, this
> becomes more difficult. For the PRS-10 some form of heatsink is pretty much
> required to keep the electronics cool enough. Although I seem to remember
> reading somewhere that the "benchtop" heatsink they offer now is lighter
> than older units.
> 
> If the room temperature is not stable enough, you might want to increase
> the size of the heatsink and add a fan. This reduces the temperature swing
> inside the unit, while still cooling the electronics, at the cost of
> increased power draw for the heater.
> 
> 
> 
> 
> On Wed, Oct 21, 2020 at 5:38 AM Hal Murray <hmurray at megapathdsl.net> wrote:
> 
>> 
>>> I spent a lot of years buying Rb’s and putting them on small heatsinks.
>> I
>>> always was disappointed in their reliability. That continued to be the
>> case
>>> up to the point that the baseplate temp’s got into the 40C region.  In my
>>> case, that took a fan ….
>> 
>> How well did it work if the heat sink wasn't small?  What is your version
>> of
>> small?
>> 
>> Do you have any data (or vague memories) of how much it helps to orient
>> the
>> heat sink so the fins are vertical so they encourage warm air to flow up
>> past
>> the fins?
>> 
>> --
>> These are my opinions.  I hate spam.
>> 
>> 
>> 
>> 
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