COLD VT  OPERATION ON THE VARIAN 500

Inverse or BB probe on the 500 can be used from  – 80^o C  to  + 130 °C

Low temperature VT is based on the flow rate of gas to control the “coldness” and the heater controlling to the exact temperature.   So you “overcool” and then nudge up with the heater.

KNOW WHERE THE EMERGENCY EJECT BUTTON IS!!

KNOW WHERE THE EMERGENCY SWITCH ON THE HEATER IS!!  (for overheating only)

ANY RAPID CHANGE IN TEMPERATURE CAN DAMAGE THE PROBE – DON’T!!

LOW TEMPERATURE BETWEEN - 30^oC AND + 25^oC using the FTS system

If you are going between   > -30^oC and <25 °C you may use the FTS system which is always on.  This controls with refrigeration the air coming into the probe...it cools it down below where you want to be and then the probe heater brings it up to the desired temperature.

1.      Put in your sample in the normal way.  Lock  and  shim.  Take RT spectrum if desired. [Always keep your eye on the lock level and the spinning in the acqstat window as this is the first sign something is going wrong.  If the sample freezes, the lock level will drop out.  If you have moisture in the lines, the sample will not spin.]

2.      Type “temp” on the command line, to bring up window.  Select a temperature, using the slide bar around 8 °C.  Select SP2  ( 0 °C)  on the FTS unit. It should start going to 0 °C.

3.      Set the VT flow rate on the magnet leg box to ~ 15. DO NOT EXCEED ~ 18 or the tube might start to lift in the probe. Watch the spinning rate as this will indicate a problem.

4.      Type “su” on the command line. DO NOT TYPE ANYTHING ELSE..WAIT FOR THE BEEP .... The beep means that it is stable, and it will say “setup complete” in the text window.

5.      You can now slowly lower the temperature and take spectra.  Lower the temperature on the slide bar, no more than 15 degrees at a time.  You should give the sample ~10 min to equilibrate at a different temperature, and you should re-shim.  DO NOT GO FAST!!

IF YOU ARE DOING CARBON YOU WILL NEED TO RETUNE THE PROBE FOR H & C at YOUR FINAL TEMPERATURE - FOR PROTON RETUNING GIVES A BETTER SPECTRUM

6.      If you need to go lower (0  to  -20), now select SP3  ( -20 °C)  on the FTS unit, and it will move to    -20.  Set your new temperature in the “temp” window; type “su” and wait for equilibration; re-shim.  To go lower in temperature  ( -20 to  -30)  select SP4 ( -40 °C) on the FTS. Set the slide and wait for equilibration, then reshim.   GO SLOW!     DO THIS STEPWISE; don’t just hit SP4 and go for it!

7.      When you are done, set the FTS to SP1  (20 °C)  and raise the temperature control bar by increments of 15 degrees. Take your time!  At the end, set the VT flow rate back to ~ 10

          SP1    above  20  °C                                         SP2        0   to  20  °C

          SP3    0  to  -20    °C                                       SP4      -20 to -40    °C   

LOW-TEMPERATURE   – 80^oC   to   +25^oC USING LIQUID NITROGEN

If you are going below < - 30 °C   YOU MUST USE TANK NITROGEN and liquid nitrogen in the bucket    (be sure you have a full tank and a transport dewar with liquid nitrogen).

FOR TROUBLE - DROP THE LIQUID NITROGEN BUCKET FIRST !!!   Bring the temp up to 15 °C.

KNOW WHERE THE EMERGENCY EJECT BUTTON IS !!  (get that sample out-overheating or cooling)

KNOW WHERE THE EMERGENCY SWITCH ON THE HEATER IS !!  (for overheating)

ANY RAPID CHANGE IN TEMPERATURE CAN DAMAGE THE PROBE – DON’T

1.                  Turn on the nitrogen tank at about 60 lbs (blue line). Turn off the air  (yellow lever). Turn on the nitrogen (red lever) (off is perpendicular -- on is parallel to the pipe)

2.                  Type “temp” on the command line, to bring up the window.  Turn the VT OFF – make sure it stays   off.   Watch the temperature decrease until it stops around 20 °C (FTS temp).

3.                  Remove the big black tube from the probe, and turn off the FTS (both switches).

4.                  Disconnect the tee with the incoming lines (quick disconnect) from the back of the FTS and connect it to the input of the coil in the bucket. 

5.                  Check to see if the nitrogen is flowing through the coil. Then hook up the output of the bucket to the probe where you had removed the big black FTS connection.

6.                  Hit the “reset VT” button, then turn the temperature control “on” and slide to select 15 °C.

7.                  Check to see that the VT flow rate on the magnet leg box is ~ 8; then wait about 5 minutes for the line and coil to flush thoroughly with nitrogen.

8.                  Take out the black rubber stopper in the white Styrofoam bucket and then pour liquid nitrogen from a dewar into the bucket. Make sure the coil is covered.

9.                  Type “su” on the command line and wait for the beep, when 15 °C is reached.

10.              Watch the acqstat window.  It should say “status: VT regulation” on the top, then “setting:        15 °C” and the  “actual temperature”  (temp is also in red digital display on left of monitor).

11.              If it goes down too far too fast, lower the VT flow rate on the gas leg a little but no lower than five.   As you go down in temperature you should raise the flow rate back to ~10. This flow rate controls the “coldness” you are adding.

12.              Put in your sample in the normal way.  Lock and shim.  Always keep your eye on the lock level and the spinning in the acqstat window as this is the first sign something is going wrong.  If the sample freezes (or boils), the lock level will drop out.  If you have moisture in the lines, the sample will not spin.

13.              You can now slowly lower the temperature and take spectra.  Lower the temperature on the slide bar, no more than 15 degrees at a time.  Give the sample ~10 min to equilibrate at a different temperature, and you should re-shim.  DO NOT GO FAST!!

14.              When done, raise the temperature control bar by increments of 15 degrees, take your time!  At a steady 15 °C, lower the bucket from the coil and turn OFF the VT.

15.              When the frost is gone from the coil and temperature is above 15, quickly turn off the nitrogen tank and then the red nitrogen lever, turn the air back on with the yellow lever.   

16.              Now reverse the procedure.  Remove the input line from the bucket to the probe.

17.              Remove the tee from the gas input line to the bucket and put it back on the back of the FTS system.

18.              Turn on the FTS with the desired temperature at 20 °C (SP1).   When it is at 20 °C, reconnect the large black line from the FTS system to the probe.

19.              Turn on the VT to 25.  Several hours later you should wipe the Styrofoam bucket dry and put the bucket back up.  Leave the black stopper off for the rest of the day.

       NEVER TURN OFF THE CONTROLLER WITHOUT FIRST DROPPING THE BUCKET.

SHOULD YOU HAVE TO STOP IN THE MIDDLE .....DO NOT TURN OFF THE CONTROLLER.