Cooled enclosure for Eshel spectrograph

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Cooled enclosure for Eshel spectrograph

Postby Olivier GARDE » Sun Apr 26, 2015 3:40 pm

This weekend , I worked on the modification of a cooled wine cellar to keep the Eshel spectrograph at a constant temperature.

Image

Image

Next step, the development and programing of a PID for temperature regulation.
LHIRES III #5, LISA, e-Shel, C14, RC400 Astrosib, AP1600
http://o.garde.free.fr/astro/Spectro1/Bienvenue.html
Olivier GARDE
 
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Re: Cooled enclosure for Eshel spectrograph

Postby Andrew Smith » Mon Apr 27, 2015 1:53 pm

Olivier, what temperature stability are you trying to achieve? Also what wavelength stability?

Nice work on the cooler do you have one for wine as well?

Regards Andrew
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Re: Cooled enclosure for Eshel spectrograph

Postby Olivier GARDE » Tue Apr 28, 2015 7:21 am

Hello Andrew,

With my eshel spectrograph, at ambiante air temperature (room about 20°C), when the temperature go up about one degree Celcius, the shift of the wavelength (mesure with Thorium lamp) is about a maximum of 0,4 pixel (in the blue part of the spectrum : order 52) and about 0,3 pixel around H-alpha.

According to the dispersion of this spectrograph with my CCD, about 0,176 Å/pixel, the variation at ambiante air (no régulation) is about 0,07 Å/pixel.

I will try to do a regulation about 0,1 - 0,2 deg Celsius with PT100 sensor class A (I can have some better accuracy if I use DIN 1/10 sensor plus it's too expensive).

So I expect to have about a maximum of 0,1 pixel shift with this regulation. (0,017 Å/pixel)

The main problem is to find the right settings for the PID regulation module.

For my wine, I have a real cellar under my house with a constant temperature of 11°C all around the year ;)
Just natural regulation here...
LHIRES III #5, LISA, e-Shel, C14, RC400 Astrosib, AP1600
http://o.garde.free.fr/astro/Spectro1/Bienvenue.html
Olivier GARDE
 
Posts: 1043
Joined: Thu Sep 29, 2011 6:35 am
Location: Rhône Alpes FRANCE

Re: Cooled enclosure for Eshel spectrograph

Postby Andrew Smith » Tue Apr 28, 2015 3:16 pm

Olivier, I was many years ago a control engineer and tuned PID controllers for a living! If I remember correctly (it is 30 years ago) with the I and D set to zero you increase P until you get uniform oscillations then set it to one half this value. Unfortunately we were not allowed to use this method on distillation columns or chemical reactors! Then tune D to get a suitable response to a step change in set point. Set "I" to remove any offset over a timescale you think suitable. It is best to play with I and D by changing the set point and seeing how long it takes to settle down. If you get oscillations when increasing D or I try half the value.

I suspect the fastest change in temperature you will get is when the camera is turned on and it starts cooling. One place where a water cooled camera is a benefit. You could add mass in your enclosure and or insulate the Eshel even in the enclosure.

I hope you get the results you are looking for.

Regards Andrew
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Re: Cooled enclosure for Eshel spectrograph

Postby Olivier GARDE » Wed Apr 29, 2015 6:33 am

Andrew,

Thanks you for your answer, my main problem is that I haven't any experience with PID programming.
I try to get some informations, and some weeks ago, I met the technician who performed regulation on SOPHIE spectrograph at OHP on the 1m93 telescope (first discovery of an exo- planet in 1995).
They also use PID (eurotherm) for regulation and 8 temperatures sensors put on different parts of the spectrograph (slit, grating, fiber output, etc..). the regulation is very accuracy (about 0,01°C at 20°C ambiante temperature).

If you have some more information about how to program a PID for regulation, don't hesitate to send me it.....

Olivier
LHIRES III #5, LISA, e-Shel, C14, RC400 Astrosib, AP1600
http://o.garde.free.fr/astro/Spectro1/Bienvenue.html
Olivier GARDE
 
Posts: 1043
Joined: Thu Sep 29, 2011 6:35 am
Location: Rhône Alpes FRANCE

Re: Cooled enclosure for Eshel spectrograph

Postby Andrew Smith » Wed Apr 29, 2015 8:43 am

Olivier - My old books are long gone but i had a quick "Google" and found this that looks straight forward and covers some of the implementation issues http://www.scilab.ninja/doc/b4/pid.pdf I hope this helps.

I have been doing some tests on my home made echelle and looking at the Ar lines (I use a lamp starter as reference) in order 40 and the O2 lines cropped from order 33 I get mean shifts of 0.023 +/- 0.3km/s and 0.000 +/-0.5km/s respectively for real world observation of 30 minutes with calibrations taken at the beginning and end of the target exposure. The figures are the mean and standard deviations from 8 sets of observations and the standard deviations represent 0.03 and 0.05 of a pixel respectively. I used ISIS and it's CCF routine to measure the shifts.

I may follow your lead and look at a temperature controlled enclosure at some point in the future but currently I have gone for a high thermal mass and thick insulation with the CCD cooling unit outside the enclosure.

Regards Andrew

PS when I originally posted this I had forgotten that I had been used to a real time operating system that took care of the interrupts need for keeping the strict timing of the algorithm. The paper does not cover these issues. I think I would go for a hardware controller myself as it is 40 year since I did any serious programming which was in FORTRAN on a PDP11 before that it was an Alpha with real ferrite core memory!
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Re: Cooled enclosure for Eshel spectrograph

Postby Martin Dubs » Wed Apr 29, 2015 12:30 pm

Hi Andrew and Olivier,

I have some experience with echelle stability. The biggest problem I found with the heating produced by the camera cooling. I solved it by bolting a water cooled alu plate to the back of my camera, a SBIG 8300. For good thermal contact I inserted a sheet of tin foil.
echelle water cooling.jpg
echelle water cooling.jpg (103.42 KiB) Viewed 3939 times

For the cooling I used a big pot of water, which kept the temperature stable within 1 degree during the night. Even better would be to put some block of ice in, a very simple temperature stabilization.
For the sensitivity of my echelle I measured a shift of 0.015A/°C at 6257 A, corresponding to a radial velocity shift of 750m/sec/°C. Compare this to a change of radial velocity by the index change of air of about 300 m/sec/°C or by air pressure of 80 m/sec/mbar.
Another point to consider for high precision radial velocity measurements is a shift of calibration lines to the star spectrum if the f-ratios of the two light sources are not identical. This gave in my case errors of up to +/- 500 m/sec within one order, checked by cross correlation of water lines in the H-alpha region, in addition to errors caused by temperature drift. The cause for these shifts are coma errors of the lens, in my case a Canon 85mm lens, which is also used in the eshel. For details about this see:
http://arxiv.org/abs/1001.0794

Regards,

Martin
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Re: Cooled enclosure for Eshel spectrograph

Postby Olivier GARDE » Thu Apr 30, 2015 6:18 am

Andrew, Martin

Thank you for sharing your experience.

I will try this weekend to test the stability of my spectrograph inside the cellar.
LHIRES III #5, LISA, e-Shel, C14, RC400 Astrosib, AP1600
http://o.garde.free.fr/astro/Spectro1/Bienvenue.html
Olivier GARDE
 
Posts: 1043
Joined: Thu Sep 29, 2011 6:35 am
Location: Rhône Alpes FRANCE

Re: Cooled enclosure for Eshel spectrograph

Postby Olivier GARDE » Wed Jul 29, 2015 4:43 pm

Here's my spectrograph room that I just finished today
Image
Equip with an industrial computer for the spectrograph CCD and to control the calibration modul.
A Nanodac PID regul the temperature of the wine celar witch was customized for the e-shel spectrograph
Image
All power supply for mount, CCD and telescope are here and remotely control (with IPX800 Module)
The celar is filled with bottled water and ice pack to obtain a thermal inertia
Image
And the computer screen is fixed on the wall .
Image
LHIRES III #5, LISA, e-Shel, C14, RC400 Astrosib, AP1600
http://o.garde.free.fr/astro/Spectro1/Bienvenue.html
Olivier GARDE
 
Posts: 1043
Joined: Thu Sep 29, 2011 6:35 am
Location: Rhône Alpes FRANCE


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