Using Thermocouples

I think you should wait for 1-2 hr to stablize the require low temperature and also during the test try to maintain the low temp continuously.
what technique are you using for doing low temperature?
I have encountered the same problem while testing Al. amit

I think you should wait for 1-2 hr to stablize the require low temperature and also during the test try to maintain the low temp continuously.
what technique are you using for doing low temperature?
I have encountered the same problem while testing Al. amit

No matter what you do your specimen will warm up when you open the door. You don't need a thermocouple to tell you that.
I don't understand what Class A or B are or what material/property/component you're testing.
You may have to devise a way to perform your test without opening the door or convince the people involved that the intent of the -30C requirement can be met if you can perform the test within +/-X deg C.
Lance *****
Vicky wrote on 3/19/2006 6:42 AM:

If you would really, REALLY like to follow the letter of the test, you could make up an acrylic window for the cooler door, and clamp a pair of long silicone rubber elbow gloves in window apertures. Then you would hold the surface temperature for sure, while executing the test. Another idea: NASA Tech Notes are showing a method to place very fine thermocouple wires without disturbing a specimen too much: they drill a very very small hole in the surface, plant the wires and crimp the hole over.
But here's the observation I should have made first: thermocouple readings are not controlled just by the "hot" (in your case cool) junction, but by the connections at the far junctions too.
Brian Whatcott Altus OK

If you don't want the surface temperature to rise, you must maintain the -30C environment. Therefore if the test takes greater than the time to loose temperate tolerance, you can't open the door. You need to either use controlled arms and a viewing panel or have a -30C room large enough for the test.