[time-nuts] Used Rb Operating Lifetime

[Magnus Danielson]

David,

On 12/31/2011 08:30 PM, David wrote:
> I agree that they are an amazing value but what kind of operating
> lifetime do the Rb tubes have?  SRS has this to say:
>
>> Historically, the lifetime of rubidium frequency standards has been
>> dominated by rubidium depletion in the discharge lamp. To avoid excess
>> flicker noise, manufacturers would load less than 100 µg of rubidium
>> into spherical discharge lamps. The PRS10 uses a lamp with a side arm
>> loaded with 1 mg of rubidium. This design eliminates rubidium
>> depletion as a failure mechanism, and provides better temperature
>> control without excess flicker noise.
>
> http://www.thinksrs.com/products/PRS10.htm

Check out page 192 (page 6 in the PDF):
http://tycho.usno.navy.mil/ptti/1990/Vol%2022_13.pdf

It says:

The tests showed, that the basic aging process of the gas-discharge tube 
can be explained by surface conductance, caused by the influence of HF 
discharge plasmia on glass surface when alkali metal vapor is used. In 
its turn it creates a systematic frequency drift due to a light beam 
shift and shortens the lifetime of the gas-discharge tube. To decrcase 
the influencs of these factors, the rubidium standard utilizes the 
reduction mode. When the instrument is turned on, the gas-discharge tube 
is warmed up in a short time up to the temperature (200-250)°C. The 
conductivc film, formed on the internal tube surface, is broken and 
gas-discharge is ignited in the norrnal way. The reduction mode allowed 
us to increase a gas-discharge tube lifetime and improve the 
metrological parameters of the rubidium standard.

It should be mentioned that this comes out of a lab being quite serious 
about their materials etc. and they build impressive hydrogen masers.

The CH1-78 rubidium lamp looks like nothing I've seen elsewhere. It's a 
one of a kind.

So, they essentially did what I did with the heat gun, heat it up 
properly. This technique was not "invented" by me, I in turn had picked 
it from Gerald Molenkamp VK3GJM for the FRS-C:
http://www.vk3um.com/Rubidium%20Standard.html

Cheers,
Magnus