[time-nuts] Heated crystal? & Rb tube corrosion (FE-5680A)
bell.peter at gmail.com
Thu Dec 1 08:14:03 EST 2011
All I can say, on a purely practical level, is that every Rb vapor
frequency standard I've ever seen or worked on (starting with the old
Eframtom FRK) has run the lamp at about 100c and the Rb cell at about
80c - the exact temperatures seem to vary a little depending on the
model, but that's how it seems to work in practice.
I just had a look at some of the manuals I have around here, and they
seem to agree (Efratom FRS, Page 3-1) - "Rubidium in the lamp is
heated to a vapor state (approximately 106C) and subjected to a high
energy RF field". Later on (Page 3-8) "Cavity temperature of about
74C is maintained by the resonator heater control circuit".
I can't find my FRK manual, but from memory it was about the same.
>From the LPRO-101 manual: "The resonator heater power is determined
primarily by the resonator control
temperature of +78°C, the baseplate temperature, and the 15.3 C/W
thermal resistance from the
resonator to baseplate. The lamp heater power is determined primarily
by the lamp control temperature
of +110°C, the baseplate temperature, and the 53 C/W thermal
resistance from the lamp to
"The block temperature is sensed by two series
100kΩ thermistors, which are directly beneath the TO-220 heaters in
the oven block. (Two
sensors are used because the division of power will depend on the
heater voltage applied to
the unit.) At the operating temperature of 75°C, each thermistor will
have a resistance of
about 15kΩ. The control circuit will allow operation up to 90°C. (For
the lamp, the nominal
operating temperature is 105°C, for which each thermistor will have a
resistance of about
5.5kΩ. The maximum setpoint for the lamp is 122°C.)"
On Thu, Dec 1, 2011 at 7:21 PM, Steve . <iteration69 at gmail.com> wrote:
> Searching for "journal of applied physics Rb oven" I found an older
> document which seconds what I had thought.
> On Thu, Dec 1, 2011 at 6:16 AM, Steve . <iteration69 at gmail.com> wrote:
>> Are you sure its is 130c, and not 130f? I can't really cite where i read
>> it, Maybe the journal of applied physics, but i was under the impression
>> that we not want to run an Rb oven much beyond 80c. Ideally i believe it
>> was 50c, but the warm up time was a few weeks.
>> I'd like to know why they need to run so hot
>> On Thu, Dec 1, 2011 at 6:04 AM, Steve . <iteration69 at gmail.com> wrote:
>>> Great pictures, by the way.
>>> My experience with alkaline metal is limited to sodium, potassium and
>>> lithium. Mostly sodium, which after a long process is precipitated from
>>> sodium hydroxide as a reagent. These are all contained in an oven under
>>> very precise temperature and flow control, as the analytes which are passed
>>> over change very specific attributes of a cell. These are the results which
>>> are reported. Eventually the cell fails and the alkaline metal attacks the
>>> cheaper mounting hardware(even though the oven maintains an argon
>>> atmosphere). If not caught in time it will work it's way down the
>>> thermocouple, under the sheath and in to the support electronics. Rb is
>>> claimed to be much more active than any of the metals i have experience
>>> with so i assumed that corrosion was a preliminary sign of low life span.
>>> For completeness, I maintain the instruments in an environmental
>>> analytical laboratory. (Sulfur analyzers, CO2, CHN, Calorimeters, ion
>>> chromatograph, inductive couple plasma mass specs, gas chromatography mass
>>> spec, organic carbon analyzer. etc,etc,etc.)
>>> When i say alkalines i mean alkalies, ie, elements which belong to the
>>> alkalinity group. 99.9999% or better purity, traceable grade.
>>> On Thu, Dec 1, 2011 at 5:36 AM, Attila Kinali <attila at kinali.ch> wrote:
>>>> On Thu, 1 Dec 2011 05:19:24 -0500
>>>> "Steve ." <iteration69 at gmail.com> wrote:
>>>> > Looking at those pictures with a different mind set, I see now that the
>>>> > washers are not corroded as I had suspected. It's amazing how they
>>>> > resemble badly corroded washers which are so typically found in ovens
>>>> > which alkalines have leaked.
>>>> If you mean "alkaline batteries leaking" with "alkalines leaking",
>>>> then the corrosion you see there is from something else than
>>>> alkali metals. In alkaline batteries you have a potpury of different
>>>> highly reactive stuff. What exactly corrodes what and how is something
>>>> i cannot tell you, but it's definitly not elemental alkalimetals like
>>>> you have in Rb cells.
>>>> Attila Kinali
>>>> Why does it take years to find the answers to
>>>> the questions one should have asked long ago?
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