[time-nuts] Newbie with new questions: Rubidium

Chuck Harris cfharris at erols.com
Tue Aug 9 14:59:26 EDT 2005

My 5065A came to me after suffering a short in the
oven heater winding.  The heater is a bifilar wound solonoid
coil built to cancel any magnetic field that the heater current
would produce (which would steer the Rb filters).  The winding was
made of enamel coated nichrome wire (about #36 gauge).  Well,
The enamel probably had a small scrape between two of the windings,
and shorted the oven out so that all of the current was concentrated
in the small section of the coil that surrounded the lamp and its
circuit board.  The oven got so hot that the solder on the lamp board
melted and flowed away from the joints.  The PC board was a nice
chocolate brown in color.  Interestingly enough, it didn't blow any
thermal fuses (there weren't any!).

I scraped away the excess "carmelization" from the board, and filled in
the fibers with epoxy, and resoldered the empty solder joints, and the
lamp came right up.  I rewound the heater with a coaxial heating element
and everything was ducky.

Until some part in the main chassis blew.  I haven't had time to go back
to it.


jim_johnson at agilent.com wrote:
> Hi Robert,
>     I guess you're talking about real "failures",
> rather than predictable wearout mechanisms (lamp death).
> My lamp failure is similar to tires wearing out on
> a car.  One doesn't consider the car to have "failed"
> just because the tires have worn out.  Anyway, we
> have certainly seen the common failures you mention.
> My first job out of school was on a project for HP to
> design a mini-rubidium source.  We used a transistor
> to heat the oven mass and I remember cringing at that
> thought since I had just learned that heat was a
> transistor's worst enemy!  I watched somebody else go
> through the design and verification of a power oscillator
> used to drive the lamp ... a few failures there, too.  :-)
> Tnx,
> Jim
>>-----Original Message-----
>>From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
>>Behalf Of Robert Lutwak
>>Sent: Saturday, August 06, 2005 5:11 AM
>>To: Discussion of precise time and frequency measurement
>>Subject: Re: [time-nuts] Newbie with new questions: Rubidium
>>The lamp runs quite hot (typically over 100C).  Failure is 
>>generally the 
>>heater, which is typically a transistor or FET bolted to the 
>>lamp body. 
>>Occasionally, the RF transistor which drive the lamp discharge 
>>(something in 
>>the range of 60-150 MHz) will fail.  Again, it's the 
>>electronic components 
>>failing, not the physics.
>>In a very old Rb, you may see some reduction in signal level due to 
>>darkening of the lamp glass.  This may lead to diminished stability 
>>performance and contribute to long-term frequency drift, but 
>>is unlikely to 
>>cause lock failure.
>>Robert Lutwak, Senior Scientist
>>Symmetricom - Technology Realization Center
>>34 Tozer Rd.
>>Beverly, MA 01915
>>(978) 232-1461   Voice           RLutwak at Symmetricom.com   (Business)
>>(978) 927-4099   FAX             Lutwak at Alum.MIT.edu  (Personal)
>>(339) 927-7896   Mobile
>>----- Original Message ----- 
>>From: "Magnus Danielson" <cfmd at bredband.net>
>>To: <time-nuts at febo.com>; <jim_johnson at agilent.com>
>>Sent: Saturday, August 06, 2005 7:40 AM
>>Subject: Re: [time-nuts] Newbie with new questions: Rubidium
>>>From: <jim_johnson at agilent.com>
>>>Subject: RE: [time-nuts] Newbie with new questions: Rubidium
>>>Date: Fri, 5 Aug 2005 16:45:17 -0700
>>><65213341217E8D458E7C78E6640C749503BB3177 at waglmb01.labs.agilent.com>
>>>>Our experience has been that the most common
>>>>failure in Rb standards is the Rb lamp.  There
>>>>is a known wearout mechanism in the lamp and
>>>>a somewhat predictable lifespan.  The filter
>>>>and absorption cells have no wearout mechanism.
>>>Some Rubidiums have a "hot-swap" of the Rubidium lamp, such 
>>as my R&S 
>>>Unfortunatly I don't have the replacement part.
>>>With hot-swap means that all electronics, heating etc is all 
>>running as
>>>normally, but during the operation there is a natural loss 
>>of tracking.
>>>>Have a nice weekend,
>>>>Agilent Laboratories
>>>>Palo Alto, CA
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