[time-nuts] 10811 foam enclosure
EWKehren at aol.com
EWKehren at aol.com
Sun Jan 9 14:07:30 UTC 2011
Being a Shera Fan I finally broke down and bought a Tbolt. I experimented
with a foam enclosure with roughly 1 centimeter on all sides. What I found
that it only increased the board temperature by 19 C. It was still as
sensitive to ambient. Thanks to Lady Heater it even shows an increase of 40 mC
when I walk up to it with one minute delay.. Changing to an aluminum
extrusion the increase is only 7 C and the response is much slower. In its final
assembly it will be inside a larger metal mass, I do not think that the
higher temperature of 56 C is conducive to longer life. Opinion: putting foam
around a 10811 will only give you a warm feeling unless you make it much
larger than shown in the picture of of KH6GRT.
Based on the above test results I feel mass is more important. So I took a
aluminum enclosed dewar weighing 943 gr. and did first put a resistor in it
and heated it up with 2 W. Temp. did rise to 70 C. Next I disassembled my
worse 10811, which is very easy, since it is a nice compact unit and
inserted it in the dewar. Monitoring temp with my YSI it shows 65.2 C with 24 C
ambient. Power dissipation is 1.575 W. Will track it over time before I
replace the 10811 with one of my better ones for frequency tests.
Questions to our experts:
A) will Removing the foam mess with the temp. control loop
B) How low can total power into the 10811 be before temp control can become
a problem, I think I am ok now, but once in a chassis with Shera and
power and battery the temp. surrounding the dewar may become a problem.
C) What is the preferred orientation of the unit.
I asked already once before if any one has data on the 1 1 PPS output of
the Tbolt over time, since I am considering it as an alternative to a stand
alone GPS receiver, and if there are GPS receivers that outperform a Tbolt
what is the recommendation. It will be used to control a Rb.
In a message dated 1/7/2011 8:22:51 P.M. Eastern Standard Time,
tvb at LeapSecond.com writes:
Has anyone experimented with the amount of insulation on a
10544 or 10811 oscillator? They are meant to run hot by
design and I worry that adding any insulation, or too much
insulation, will either cause over-heating or limit the ability
of the oven control to maintain the set point.
None of the hp/Agilent bench test equipment that uses these
oscillators uses insulation. Perhaps that's a clue.
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