This is true for most vt controller. You should try to reach your desired
temperature in steps (~10 degree) instead of typing the final desired
temperature at once. For going to high temperature, the heater turns on
and the temperature overshoots. The actual temperature will be higher for
some time than you desire. At low temperature, the heater stays off, and
the temperature follows the cold gas for sometime before the heater turns
on.
You may also like to pull out the temperature controller and check for any
flaky connection between the controller and the probe
Sandip
>Pardon the double posting.
>
>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
________________________________________________________________________________
Sandip K. Sur, Ph.D. Email: sur@chem.chem.rochester.edu (W)
NMR Facility
Department of Chemistry Tel.: (716) 275 4705 (W)
B53B Hutchison Hall (716) 275 0912 (W)
River Campus (716) 586 7794 (H)
University of Rochester Pager: (716) 275-4231 (ask for me)
Rochester, NY 14627-0216 Fax: (716) 473 6889
Wednesday, February 17, 1999
________________________________________________________________________________