Susan J. Kohler

June 19, 1997

There are two probes for the 400 MHz spectrometer. One is for 5mm samples, the other is for 20mm samples. To change probes, it is necessary to change both the probe which comes out of the bottom of the magnet and the insert which goes in the top.

Start by removing any sample which may be in the probe. This is done via the keyboard by typing "ej" or by using the Lift On/Off button. Once the sample is out, type "ij" or hit the Lift button again to turn off the eject air.

Next remove all cables from the bottom of the probe. This will include three black coaxial cables with BNC connectors. You will also have to remove the gradient cable (the connector is a twist-lock) if you are taking out the 5mm probe. Next remove the temperature control apparatus from the bottom of the probe. This includes the heater (spring loaded connector) and the thermocouple if it was put in previously. The thermocouple connector just pulls out. Everything up to and including the brass fitting comes out. Remove the air line (green) which also is attached to the probe.

Now all the connections to the probe should be off, and you can take out the probe itself. Hold one hand on the bottom of the probe, and with the other hand move the big handle on the right side of the probe housing away from you. This releases the probe, and it should come out the bottom of the magnet. Put it in its foam-lined box for safekeeping.

If you are changing from the 5mm probe to the 20 mm probe, you have to remove the insert from the top of the magnet. There are two connections to move from the insert to the wider ring at the top. One is the gray line in the back which measures the spinning speed. This connector unscrews. Remove the line, and place it on the appropriate connector on the wide ring. Be careful to orient the connector the right way before trying to screw it in! The second line to move is the yellow air line. To detach it, you must push in on the yellow ring while pulling out on the yellow hose. Once you get it off, just push it on to the similar connector on the big ring. (Tug a little to make sure it is firmly in place.) Then you should be able to pull the insert (with the white ring, too) out of the top of the magnet. You will feel some resistance due to the eddy currents induced by moving the metal in the magnetic field. Just pull slowly and be patient. Place the insert in its protective box.

To insert the new probe, simply wipe it off, and insert it in the bottom of the magnet. The connectors on the bottom will face left, toward the inner wall of the NMR room. When it is almost all the way in, make sure the two prongs line up with the square holes in the bottom of the magnet. Push it the rest of the way in, then pull the lever toward you to lock it in place. Reattach all the cables, including the gradient cable if you just put in the 5mm probe. Obviously you should take care to attach the appropriate cable to the appropriate connector, as marked. Attach the green air line, and insert the heater (this is needed even if you do not plan to do temperature-controlled work). If you plan on doing temperature controlled work, insert the thermocouple into the little hole in the base of the probe. If you don’t need it, you may leave it out, but make sure it is in its protective sheath.

If you just inserted the 5mm probe, you must put in the insert from the top of the magnet. Simply wipe it off and put it in. Then move the two cables from the outer ring to the insert (see above).

After completing the probe installation, it is necessary to tell the system which probe is in place, and to load the proper shim values. At the keyboard within the xwinnmr program you must type "edhead" to call up the probe menu. Then click on the Define Current button and select the proper probe from the list. Then click the Save button. Then type "rsh" to read in a shim file. Choose the appropriate file.