Shaoxiong Wu, Ph.D.
Director, NMR Research Center
Emory University
404-727-6621
>The VT unit on our QE-300 is driving me nuts. It has become
>unpredictable,
>sometimes it will go to the desired set point and maybe the next entry it
>will run-away. For example, if I enter the set point of -78 the temp will
>drop as it should, but it may continue to to drop past the set point. If
>I
>retype the set point of -78 a couple of times it seems to finally catch
>and
>go to the desired temp. If I increase the temp from -78 to -40 it will go
>past this point and continue to rise. It reached +74 before I ejected my
>standard. The tube was hot so the thermal couple seems to be reading the
>actual temp on the run aways. The VT seems to work sometimes and goes to
>the entered set point, it may do this a couple of time before it will run
>away again. Once it does reach the desired set point it is rock solid
>until it is changed to another temp. The flow rate of the N2 is set
>correctly so I don't think that is the source of my problems. It will
>also
>run-away on the house air when high temp experiments are carried out.
>
>If anyone has an idea about about the source of this problem or has had a
>similar experienced please let me know how to solve it. Of course this
>always seem to happen when someone has to do a critical experiment for a
>paper at the request of a referee or a thesis committee.
>
>Thanks in advance,
>
>Chuck