[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.
Bert Kehren. 
 
 
In a message dated 1/17/2012 2:52:47 P.M. Eastern Standard Time,  
warrensjmail-one at yahoo.com writes:

to  Chris
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 
a 
closed 'oven box' below 0.1 deg is also NO problem.

to  Bert
Have you measure what the Temperature coeff is over normal room  changes 
with 
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 
the 
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 
stable 
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 
changes 
the temperature set-point of  the heat source's temperature control  loop.

ws

***************
>I am, as I reported previously  using a SMD LM335 away from the fan and 
held
> 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 
look
>  more professional.
>Bert Kehren

*************
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.

>>Chris Albertson
>>Redondo   Beach,  California  


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