Notes on Variable Temperature
IN AN EMERGENCY:
If the power fails, the gas supply is interrupted, you notice a burning smell, etc., IMMEDIAY STOP ALL VT ACTIVITIES:
1. Immediay type temp='n' su
2. Immediay set the FTS pre-conditioning unit to 20C.
3. Immediay remove the liquid nitrogen bucket if you are using it.
4. Immediay contact the NMR Facility staff.
5. Immediay remove your sample.
6. In extreme emergencies:
A. Walk around the magnet to the back of the I-400 console. DO NOT walk between the magnet and console through the cables & circuits.
B. Turn OFF the power to the VT unit by pressing the big red "POWER" button on the console VT unit （the console VT unit has a black panel with a POWER button, STATUS light, and LED display of the temperature）.

Troubleshooting the VT unit.
1. If you type temp=25 su and the VT display on the remote status module does NOT respond after a few minutes, type sethw（'vt','reset'） temp=25 su （this ONLY works on INOVA spectrometers）
2. If there is no change,
A. Walk around the magnet to the back of the I-400 console. DO NOT walk between the magnet and console through the cables & circuits.
B. Turn OFF the power to the VT unit by pressing the big red "POWER" button on the console VT unit （the console VT unit has a black panel with a POWER button, STATUS light, and LED display of the temperature）.
C. Wait 10 seconds, then press the big red "POWER" button again to turn ON the power to the console VT unit.
D. Type temp=25 su. The VT display on the remote status module should respond.
3. Check that there is NO CONSTRICTION in all VT hoses and that all hose connections are sealed tightly with no gas leaks. The most likely place for this constriction is between the pre-conditioning unit （or liquid nitrogen bucket） and the probe. BE CAREFUL when you check the hose connected directly to the probe: this connection may be frozen and the probe is VERY FRAGILE---be gentle, or you will break the probe!

To perform VT experiments between +25C and +90C:
1. MAKE SURE that your sample is stable at the lowest and highest temperature that you will use on the spectrometer. If your sample explodes in the magnet and destroys the probe, you will be responsible for the cost of equipment repair.
2. Type temp=25 su to regulate your sample at 25C.
3. Make sure that the FTS pre-conditioning unit is set at 20C.
4. After the temperature display on the remote status module has stabilized for a few minutes, type temp=temp+10 su. Do not increase the temperature by more than 10 degree increments. If your desired temperature is within 10C of the current VT temperature, type temp=## where ## is your desired temperature.
5. Repeat step #4 until you reach the desired temperature
6. Perform your experiment（s）.
7. When you are finished doing VT experiments, type temp=temp-10 su. Do not decrease the temperature by more than 10 degree increments.
8. Wait for the temperature display on the remote status module to stabilize for a few minutes. Repeat step #7 until the temperature is<30C.
9. Type temp='n' su to turn off the VT regulation.

To perform VT experiments between -35C and +30C:
1. MAKE SURE that your sample is stable at the lowest and highest temperature that you will use on the spectrometer. If your sample explodes in the magnet and destroys the probe, you will be responsible for the cost of equipment repair.
2. Type temp=25 vtc=30 su to regulate your sample at 25C.
3. Set the FTS pre-conditioning unit to 5C below the lowest temperature that you want to use. DO NOT set the pre-conditioning unit lower than -40C. Wait until the display on the pre-conditioning unit reaches the set temperature.
4. After the temperature display on the remote status module has stabilized for a few minutes, type temp=temp-10 su. Do not decrease the temperature by more than 10 degree increments. If your desired temperature is within 10C of the current VT temperature, type temp=## where ## is your desired temperature.
5. Repeat step #4 until you reach the desired temperature.
6. Perform your experiment（s）.
7. When you are finished doing VT experiments, type temp=temp+10 su. Do not increase the temperature by more than 10 degree increments.
8. Wait for the temperature display on the remote status module to stabilize for a few minutes. Repeat step #7 until the temperature is >15C.
9. Set the FTS pre-conditioning unit to 20C. Wait until the display on the pre-conditioning unit reaches the set temperature.
10. Type temp='n' su to turn off the VT regulation.

To perform VT experiments between +90 and +150C
1. MAKE SURE that your sample is stable at the lowest and highest temperature that you will use on the spectrometer. If your sample explodes in the magnet and destroys the probe, you will be responsible for the cost or equipment repair.
2. Inform the NMR Facility staff at least two days in advance that you will need N2 gas from the N2 boil-off tanks in the wet lab.
3. Purge the VT system with N2 gas for 20 minutes.
4. Type temp=25 su to regulate your sample at 25C.
5. The difference between the pre-conditioning unit and the sample temperature should not be greater than 60C. If the next step increases temp more than 60 degrees above the pre-conditioning unit temperature, first increase the temperature of the pre-conditioning unit. DO NOT increase the pre-conditioning unit temperature above the VT temperature. DO NOT increase the pre-conditioning unit above +90C.
6. After the temperature display on the remote status module has stabilized for a few minutes, type temp=temp+10 su. Do not increase the temperature by more than 10 degree increments. If your desired temperature is within 10C of the current VT temperature, type temp=## where ## is your desired temperature.
7. Repeat steps #5 & 6 until you reach the desired temperature.
8. Perform you experiment（s）.
9. When you are finished doing VT experiments, type temp=temp-10 su. Do not decrease the temperature by more than 10 degree increments. Decrease the temperature of the pre-conditioning unit if the temperature of this unit is higher than temp.
10. Wait for the temperature display on the remote status module to stabilize for a few minutes. Repeat step #9 until the temperature is <30C.
11. Make sure that the pre-conditioning unit is set at 20C.
11. type temp='n' su to turn off the VT regulation.
12. Switch the VT system from N2 gas to air.

To perform VT experiments from -120C to +0C:
1. MAKE SURE that your sample is stable at the lowest and highest temperature that you will use on the spectrometer. If your sample explodes in the magnet and destroys the probe, you will be responsible for the cost of equipment repair.
2. Inform the NMR Facility staff at least two days in advance that you will need N2 gas from the N2 boil-off tanks in the wet lab AND that you will need to have the liquid nitrogen bucket attached to the probe.
3. Purge the VT system with N2 gas for 20 minutes.
4. Type temp=25 vtc=30 su to regulate your sample at 25C.
5. Add liquid nitrogen to the liquid nitrogen bucket. Monitor the level of liquid nitrogen THROUGHOUT your experiment, and add liquid nitrogen when the liquid level is low.
6. After the temperature display on the remote status module has stabilized for a few minutes, type temp=temp-10 su. Do not decrease the temperature by more than 10 degree increments. If your desired temperature is within 10C of the current VT temperature, type temp=## where ## is your desired temperature.
7. Repeat step #6 until you reach the desired temperature
8. Perform you experiment（s）.
9. When you are finished doing VT experiments, type temp=temp+10 su. Do not increase the temperature by more than 10 degree increments.
10. Wait for the temperature display on the remote status module to stabilize for a few minutes. Repeat step #9 until the temperature is >0C.
11. Remove the lN2 bucket when the temperature is set to 0C or higher. Continue to warm the VT unit by following step #9.
12. When temperature equals >15C, type temp='n' su to turn off the VT regulation.
13. Switch the VT system from N2 gas to air.

To Accuray Measure the Temperature:
The temperature display on the remote status module is NOT NECESSARILY the temperature of your sample. See also Important Notes about VT: note #1. While the difference between real temp and displayed temp is usually small, this difference is larger at extremely low or extremely high temperature settings. To accuray measure the temperature of your sample, do the following before or after （or before AND after） you perform your experiment:
To measure temperatures between +20C and +90C:
1. Put the ethylene glycol temperature calibration sample in the magnet. Turn the lock OFF.
2. Bring the sample to the desired temperature.
3. Equilibrate for 10 minutes.
4. Obtain a 1D 1H spectrum.
5. Display two cursors and align them on the two resonances in the spectrum
6. type tempcal（'e'） or tempcalc（'e','####.#'）.
tempcal calculates the temperature based upon the cursor position on the screen.
tempcalc calculates the temperature based upon a number （type a number in place of ####.# in the command）. There are three variations of tempcalc for the ethylene glycol sample:
• tempcalc（'e','####.#'） calculates temperature of ethylene glycol, chemical shift difference in Hz
• tempcalc（'e','####.#','h'） calculates temperature of ethylene glycol, chemical shift difference in Hz
• tempcalc（'e','####.#','p'） calculates temperature of ethylene glycol, chemical shift difference in PPM
7. The real temperature is displayed. Record this temperature AND the VT gas flow.
To measure temperatures between -90C and +40C:
1. Put the methanol temperature calibration sample in the magnet. Turn the lock OFF.
2. Bring the sample to the desired temperature.
3. Equilibrate for 10 minutes.
4. Obtain a 1D 1H spectrum.
5. Display two cursors and align them on the two resonances in the spectrum
6. type tempcal（'m'） or tempcalc（'m','####.#'）.
tempcal calculates the temperature based upon the cursor position on the screen.
tempcalc calculates the temperature based upon a number （type a number in place of ####.# in the command）. There are three variations of tempcalc for the methanol sample:
• tempcalc（'m','####.#'） calculates temperature of methanol, chemical shift difference in Hz
• tempcalc（'m','####.#','h'） calculates temperature of methanol, chemical shift difference in Hz
• tempcalc（'m','####.#','p'） calculates temperature of methanol, chemical shift difference in PPM
7. The real temperature is displayed. Record this temperature AND the VT gas flow.

Important Notes about VT:
1. Inside the probe, the gas flows past the heater, then past the thermocouple, then past your sample
A. If gas is NOT flowing past the heater and the heater is turned ON, there will be a VERY RAPID build-up of heat inside the probe. This has two effects:
1. The probe could suffer damage.
2. You sample will start to increase in temperature. However, this increase will not be very rapid until the gas flow starts again. Once the gas flow starts again, the gas will flow past the VERY HOT heater, and then flow up to your sample, and your sample will rapidly increase in temperature. THEREFORE, if the gas flow is interrupted, immediay turn off the heater, especially before turning on the gas flow.
B. Because the heater is below the sample, every sample experiences a temperature gradient from the bottom of the tube to the top of the tube.
1. Limit your sample height from 28 to 32 mm to reduce this gradient.
2. This gradient may also cause refluxing or convection of your solvent, which will degrade the lock stability and resolution. Consult the NMR Facility staff about vortex plugs, which will reduce the refluxing of your solvent.
3. Increase the gas flow at extreme temperatures to reduce the change in gas temperature between the heater, thermocouple, and sample. （Caution: If you increase the gas flow too much, sample spinning may not work and/or your sample may rise out of the probe head, as if the sample was partially ejected）.
C. Because the thermocouple is below the sample, the temperature displayed on the remote status module and the real temperature of the sample are NOT NECESSARILY the same. While the difference between real temp and displayed temp is usually small, this difference is larger at extremely low or extremely high temperature settings. Increase the air flow to reduce this difference, especially at extremely low or high temperatures. （Caution: If you increase the gas flow too much, sample spinning may not work and/or your sample may rise out of the probe head, as if the sample was partially ejected）.
2. The normal flow of gas should be 10LPM
3. This connection between the rubber hose and the probe is VERY FRAGILE! BE CAREFUL if you move anything around this connection. Do not remove the rubber tube from the probe if the rubber is frozen---first thaw the rubber with your hand.
4. The liquid nitrogen usually lasts 1 to 2 hours. Do not run lN2 esperiments unattended for more than 1 hour.
5. If tin='y' and VT becomes unregulated during the experiment, the data acquisition is automatically stopped. The acquisition will NOT automatically resume if the VT becomes regulated again.
6. vtwait determines the length of time to wait for VT regulation before the experiment will start. The default value for vtwait is 180 seconds. If VT regulation is not achieved after vtwait, then "VT FAILURE" will be displayed on the Sun monitor.
7. With proper choices for pad and a temp array, a series of experiments can be automatically collected with changes in temperature between experiments.
8. High-power decoupling can heat your sample, which decrerases your VT stability and
accuracy. Consult the NMR Facility staff about methods to reduce heating by the decoupler.
9. The pre-conditioning VT unit has the following controls:
The UP arrow increases the temperature set point
The DOWN arrow decreases the temperature set point
The RUN key toggles the controller on/off. The unit is regulated only when the RUN light is on. If the RUN light is off, press the RUN button to turn it on.
To turn off the pre-conditioning unit:
A. turn the temperature controller to -60C.
B. Turn off the refridgeration switch
C. Let air continue to flow through the system until the exit air reaches +20C
D. Turn off the FTS "regulation" unit.
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