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Liquid Nitrogen (LN2) Pour Filled Dewar Cameras

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MrSheep:
Just a teaser for my adventure into Liquid Nitrogen Pour Filled Cameras. One benefit of these cameras over a cryocooled stirling camera is that you can change the FPA's and filters are no longer "warm" filters but "cold" filters, which increases their performance.

These cameras require a lot of additional equipment to get them going. I had to build my own vacuum system which consisted of a turbo molecular pump, diaphragm pump, a few sensors and alot of high vacuum tubing. All just to evacuate the dewar. I did not want to take the chance of pouring LN2 into a dewar that was not properly evacuated. According to the manual u need at least 1.0x10^-5 Torr.

I also had to buy a LN2 dewar and the associated accessories, such as funnels and PPE.

Although it took me a good month just to get all the equipment. I can confirm that both cameras work! I was able to obtain good images. Will post more about this in the future.

MrSheep:
This is the vacuum setup I have. Consist of a Pfeiffer Turbomolecular Pump and DCU, PKR-251 Full Range Gauge, Pfeiffer Diaphragm Pump, Edwards Pirani Gauge and Controller, isolation valves, and alot of reduces, tubes and bellows, all KF Style.

What all this ultimately attaches to is to something called a "vacuum operator". I had to look around for this as I had no idea what that was in the first place. I did a few days of searching just to figure out what this thing looked like. Essentially it is a plunger type device with vacuum seals inside. The plunger twists as well as moves in and out. This allows for the removal of the vacuum port on the back of the dewar. I was able to purchase one of these from a company called Cryofab. part number: 03V1045-3 "Operator, Vacuum Port, 1/2" w/NW-25 Flange"

I run the roughing pump first and gradually ramp up the speed of the turbo until I can easily pull out the plug. I don't want to open the dewar under high rpm because I don't know if it is under atmospheric pressure or not. I think for the future i'm going to add another gauge and isolation valve. That way I can rough down the system to about 5mbar first and check to see the vacuum pressure of the dewar. But so far my setup has worked.

MrSheep:
Reserved

KE5FX:
Interesting stuff.  Why do you have to evacuate the dewar before adding the LN2?  To avoid creating ice crystals?

MrSheep:
Yes exactly. Think of a thermos you can drink out of. There is a vacuum on the inside of it. So the dewar is basically the same concept. You want to a) insulate the surrounding atmosphere's relatively high temperature 293K (20°C) from the cold 77K (-196 °C) LN2 cooled sensor. b) Avoid any impurities and water vapor from freezing on the sensor. I think if it is bad enough it can damage the FPA sensor inside. The manual even mentions this.

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