Page 1 of 1

Towards temperature Control of my Echelle

PostPosted: Sun Jun 26, 2016 1:40 pm
by Andrew Smith
Rather than follow Olivier down the wine cooler route I have got an off the shelf PID controller and an Air to Air Peltier cooler/heater module. The initial wire it up and hope it works tests seem to have gone ok so I am now looking integrate it all an enclosure. I have yet to decide if I need to enclose the camera (ducting in and out it's cooling air or just control the temperature of the echelle enclosure. Any advice would be welcome.

Regards Andrew

Re: Towards temperature Control of my Echelle

PostPosted: Sun Jul 24, 2016 3:39 pm
by Olivier GARDE
Hi Andrew,

I am very interested about your results on this thermal regulation.

What you get in control accuracy ?

Re: Towards temperature Control of my Echelle

PostPosted: Sun Jul 24, 2016 4:29 pm
by Andrew Smith
Hi Olivier, I am undertaking some improvements to the echelle so have not implemented the cooling yet. I will publish the results as soon as I have some but it could be a few months yet!

Regards Andrew

Re: Towards temperature Control of my Echelle

PostPosted: Wed Dec 28, 2016 12:47 pm
by Andrew Smith
After much delay I am ready to reassemble my echelle. I have had to get a new grating as the old one was somehow damaged.

I have built a new housing and installed the temperature control system. The SX694 camera is enclosed within the housing and provides a load for the cooler.

The attached show the results of a 72 min log of the enclosure temperature with the camera running at -10c and a enclosure setpoint of 15c. The controller has not been tuned other than getting some rough values to get it to work and is in PI mode. You can see the initial transient as the enclosure cools from ambiant and near the end one introduced by turning off the camera. The temperature sensor is in the cabinet air at present.

Re: Towards temperature Control of my Echelle

PostPosted: Tue Jan 31, 2017 11:36 am
by Andrew Smith
The echelle is now rebuilt and in the observatory. It is now a genuine black box as it is covered in 50mm of black insulation apart from the cooler heat sink and fan. The weather has been very poor so I have simulated observing runs where the temperature control is better that +/- 0.05 degrees. The intention is to set the controller at it current temperature at the start of the run and keep it there rather than always run at a given temperature, taking Th Ar calibration spectra at the beginning and end of the run.

The attached is a combined spectrum of the inside of observatory and a Th Ar lamp as I start the process of working out which order is which somewhat complicated by the fact the image is flipped from my original set up which had me fooled for a while. This totally un-optimised extraction give 0.016 nm/px and R~8000 as designed.

Regards Andrew

Re: Towards temperature Control of my Echelle

PostPosted: Tue Jan 31, 2017 11:43 am
by Andrew Smith
PS Thanks to Olivier Garde for his Thorium & Argo lines atlas whith out it I would have been lost for a lot longer.

Re: Towards temperature Control of my Echelle

PostPosted: Sun Apr 09, 2017 11:32 am
by Andrew Smith
Hi Fran├žois, here is an update on the temperature control of my echelle. Not a lot to add from the above but I can so some data.

I went for a high thermal mass design. The picture shows the general arrangement while I was focusing the collimator. The echelle grating faces down to stop dust etc.

The base is a ceramic tile and when in use it is covered by a wooden box and the whole structure covered with 50mm of insulation apart for the slot where the Peltier cooler is fitted. I start the camera (which provides a thermal load, and the cooler controller at the same time. I don't try to maintain the same temperature between sessions as this could over power the cooler. Instead I set the temperature set point to the current enclosure temperature. The temperature is maintained by a PI control algorithm tuned to be "loose" as the thermal mass stops fast changes.

I did look for correlations between the Km/s variations and other environmental measures, pressure, ambient temperature and enclosure temperature variations but did not find any. If you do succeed with pressure control please share how you did it.

Below are the data collected from the longest stability test I did.

Regards Andrew

Echelle 1 small.png

Temp_Stability.png
Temp_Stability.png (26.47 KiB) Viewed 3070 times

Km_per_s_stability.png
Km_per_s_stability.png (7.13 KiB) Viewed 3070 times