[time-nuts] 5680A update
EWKehren at aol.com
EWKehren at aol.com
Tue Jan 17 16:55:13 EST 2012
Warren if you look close I did put a thermal barrier on the bottom and have
a large heat sink on the top with by my standards a large fan. All this
because I wanted it up and running with in an hour. I realize the sides also
radiate but putting a sensor at center on the bottom I am within 0.1 C. I
did this for testing quick and dirty and frankly never expected the
performance I se. So at some point I will package it in such a way that I will have
optimum temperature control. Right now I have a four channel Wavetek 52A
data logger but plan to build an 8 channel logging device based on a 16F688
PIC. From that data I will be able to pick the best placement of the
sensor. Keep in mind this work is intended for a limited temperature range, this
is not a commercial environment where one solution has to fit all. That is
why I work today every thing with cooling. Breaking that fancy Dewar has
turned into a blessing.
In a message dated 1/17/2012 2:52:47 P.M. Eastern Standard Time,
warrensjmail-one at yahoo.com writes:
What I've seen is that holding 0.1 C AT the SENSOR is pretty easy,
(Lady Heather will hold the TBolt's sensor to 0.01 deg using just a fan),
AND if you blow a lot of air around, then keeping the air gradients inside
closed 'oven box' below 0.1 deg is also NO problem.
Have you measure what the Temperature coeff is over normal room changes
and without the addition of the temp controller?
What is the best configuration to keep the fe5680 freq constant?
For the LPRO, what I found by experiment worked best for me is to place
unit upside down so the heat sink was on top.
If any air was blown on the non heat sink side, that would greatly effect
the frequency stability in a bad way.
A way to get around the compromise of where the best place is to put the
sensor, either close to the heat source or close to the device.
Best answer is BOTH. The way to get high end control and a much more
control loop, is to use TWO temperature sensors.
Put one temperature sensor near the Heat source and a second one at the
place you want to hold constant.
Then in effect 'AC couple' the heat source sensor, so that it does the
course temperature control.
One way to do this is to set it up so that the heat source sensor is the
feed-forward or "D" input for the main sensor PID control loop.
Another way to set it up is so that the device sensor's error slowly
the temperature set-point of the heat source's temperature control loop.
>I am, as I reported previously using a SMD LM335 away from the fan and
> down with a screw and a small bracket and I get consistent .1 C. I do not
>think that I would get 1 E-12 over weeks when my lab has seen more than
>5C temperature changes if my temperature readings are not correct.
>Do not forget this was a quick and dirty setup, the final product will
> more professional.
albertson.chris at gmail.com writes:
On Tue, Jan 17, 2012 at 8:38 AM, <EWKehren at aol.com> wrote:
>>> I am using a fan that holds it within .1 C Its been month since I
>>>measured it but I did report it here and I think it is 42.7C.
>>0.1C is very good for just using a fan. What is the fe5680
>>mounted to? just the heat sink or is there a thick metal plate.
>>Also what are you using as a heat sensor. Is the sensor press fit to
>>the heat sink or. I do remember reading about your temperature
>>controlled fan but not the 0.1C part. I'd have guessed you could only
>>do about 2.0C with a setup like yours.
>>Redondo Beach, California
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