[time-nuts] Re: poor mans environmental control for time servers (with pictures)

[Attila Kinali]

On Mon, 7 Feb 2022 13:55:23 +0100
folkert <folkert at vanheusden.com> wrote:

> https://vanheusden.com/texts/usb-asic-miner-heater/
> 
> What it is about: I've put my time-servers in a box and now them up
> using usb bitcoin miners (- they have no use anymore because they are no
> longer profitable) to 35 degrees celsius. As expected/visible in graphs,
> this stabilizes the clocks of the time-servers a bit.

Nice use of recycled electronics :-)


Some small additional notes for those who want to do the same and
use it to stabilize oscillators (OCXO, rubidium and the like)

1) If you are building a control loop, have a temperature sensor
with more than 0.1°C resolution. 0.1°C is quite a large dead-band
for a control loop in a case like this and might lead to oscillations
in the control loop. I can recommend using a BME280 break-out board
as a temperature sensor. It's relatively cheap (at least it was
before 2020), delivers temperature to 0.001°C with very little noise
(noise floor is below 0.005°C) and gives you humidity as a bonus.
Its long term stability is better than I can verify with the equipment
I have, so good enough :-)

2) Use a heating element that you can control with at least 10 bits.
It doesn't really matter whether it's some PWM with 5minutes loop time
or some heater element controlled with a DAC. Going below 10 bit will
give too little control to hold the temperature stable and thus can
lead to oscillations as well.

3) If you pass cables through the lid, tape the lid shut. Most of the
heat will be lost through convection through the holes in the lid

4) It's not explicitly written in the article, but the small fan you
see  in there is cruical. There is convection even in these small boxes
and it is very slow. You want to mix the air inside the box well
so that you don't get temperature gradients and hot/cold air bubbles
that move around.


			Attila Kinali

-- 
The driving force behind research is the question: "Why?"
There are things we don't understand and things we always 
wonder about. And that's why we do research.
		-- Kobayashi Makoto