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
Charles L. Anderson, Ph.D.
Manager NMR Facilities
Department of Chemistry
University of Houston
Houston, TX 77204-5641
Office: (713)-743-2728
Fax: (713)-743-2709
"Anything one man can imagine
others can make true"
Jules Verne