Cooling a detector
If you have a liquid nitrogen-cooled MCT detector, you must cool it with liquid nitrogen before you can measure data.
Time needed: 40 minutes or less.
Tools needed:
- Protective clothing and eye wear
- A small plastic laboratory funnel
- A one-liter, metal vacuum bottle
- Liquid nitrogen
A detector dewar should maintain its insulating vacuum for several years. If the vacuum leaks, the insulation will lose effectiveness.
 |
Avoid freeze burn hazard. Liquid nitrogen is extremely cold and potentially hazardous. Make sure you pour the liquid nitrogen slowly when you fill the vacuum bottle or the detector dewar. Pouring too quickly can cause liquid nitrogen to spray out. To prevent injury, always follow standard laboratory safety practices and wear protective clothing and eyewear when you use liquid nitrogen. Avoid letting liquid nitrogen come into contact with your skin. |
- Open the detector dewar cover and remove the plastic stopper from the dewar.
- Fill the metal vacuum bottle with liquid nitrogen.
| Do not spill liquid nitrogen on or near the detector window. If the window's o-ring seal cools very rapidly, the dewar may lose its vacuum and expose the detector element to damaging atmospheric pressure. |
- Insert the funnel into the detector dewar and pour the liquid nitrogen slowly into the funnel. A small amount of liquid nitrogen typically spills out of the funnel. This will not harm your instrument.
- Fill the funnel and let it drain completely two or three times. Wait until the vapor plume disappears and then repeat until the dewar is filled.
- Remove the funnel.
- Wait until the vapor plume disappears, and then replace the plastic stopper and close the dewar cover.
- Wait 20 minutes, and then repeat the preceding steps to make sure the dewar is completely filled.