[OpenSPIM] Temperature control for the SPIM chamber

[Jan Krieger]

Hi Johannes & all!

  > Depending how fast your temperature control needs to react (i.e. do you
> need to keep the temperature just stable? In that case, a big peltier
> underneath the plexi glass chamber should be good enough), you might need
> to anodize the side of the chamber, or put in a window as you say.
>
> Another idea would be to embed the peltier *inside* the chamber rather
> than underneath, so that you do not have to go through the complete
> centimeter or so of plexi glass.

We tried it with a Peltier, BUT: THe problem is a Peltier is a
Heat-PUMP, not a heater, so one side will be cooled, the other will get
hot. This is convenient for cooling, as you can simply put a big cooler
or a water-tube on the hot side to remove the heat (the efficiency
mostly depends on the temperature gradient over the Peltier). For
heating you have the problem that you have to get the heat somehow TO
the war side: A water-tube might again be a good solution, but as long
as you only want to heat, a simple resistor is much easier:
1. controling it with a microcontroller or a computer is very simple
(for a Peltier you need much more electronics here)
2. you don't need to worry about the heat-pump-thing, as the resistor
with resitance R and current I will simply have a heating power of
P=R*I^2 (or if you use PWM with a duty cycle p: P=U^2*p^2/R)


> Also keep in mind that you need to have a precise temperature sensor
> inside the chamber, preferably two: one close to the peltier, one as far
> from it as possible, to account for temperature gradients.
Yes that's really true: We use one PT100 close to the resistor which is
used for a PI loop and a second one inside the sample chamber to measure
the medium temperature. Typically we set the set point ~1°C above the
desired final temperature. We use PT100 with a 4-wire readout, which is
very precise.

Here are some links on PT100 and Peltier-temperature control:
http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=snoa481b&fileType=pdf
http://www.linear.com/product/LTC1923
http://www.maximintegrated.com/datasheet/index.mvp/id/3377
http://redlum.xohp.pagesperso-orange.fr/electronics/315M/TEC.html

cu
JAN

PS: I had a student working on this project with a peltier and whoever
is interested: I can give you the report he wrote. Just drop me a
message ;-)

>
> But please keep in mind, too, that I am a software guy, not a hardware
> guy, so hopefully scientists with more experience in the matters at hand
> will respond soon (I know that PAvel is at a workshop these days,
> introducing the OpenSPIM to yet another crowd of scientists, so he'll be
> busy, I suspect).
>
> Ciao,
> Johannes
>
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>




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