Loading a Probe File Probe files are typically created during system or probe installation. Procedures for creating probe files and probe calibration files are provided in the system Acceptance Tests Procedures manual. 1. Click the Probe button on the Hardware bar, at the bottom left corner of the VnmrJ interface. 2. Click the Select Probe drop-down menu and select the desired probe.
Tuning a Probe Tuning a probe using the TUNE INTERFACE remote takes the following steps: 1. Set up the spectrometer to observe the nucleus of interest. Often, the system is already set to the correct nucleus; if not, proceed as if you were setting up an experiment. 2. Two methods are available to set the tune frequency. Until you set up the tune frequencies with one of the methods (su or tune), the TUNE INTERFACE remote will not work after powering on or after resetting the acquisition console. • The first method is to enter go or su. Each time go or an su executes, the console receives a frequency for each channel defined for the experiment. This frequency also becomes the one used during tune. The table below shows the relationships between the channel selected and the associated parameters: Channel 1 tn sfrq tof Channel 2 dn dfrq dof Channel 3 dn2 dfrq2 dof2 Channel 4 dn3 dfrq3 dof3
• The second method is to enter qtune for a swept display. The settings remain in effect until the next go or su command executes. 3. Press the CHAN buttons until the readout is the number of the rf channel you want to tune. Start with channel 1. This turns on the tuning function for the channel. The TUNE INTERFACE display should shows a number. 4. Press the ATTEN buttons until the readout is 6, 7, or 8. 5. If necessary, insert the appropriate sticks into the probe. Refer to the probe installation manual as to which sticks are needed to tune to the desired nucleus. 6. Tune the probe. As the probe gets closer to being tuned, the number on the TUNE INTERFACE display will decrease.
7. Press the ATTEN button until the readout is 8, to increase the tuning level sensitivity. Continue tuning until the number displayed on the TUNE INTERFACE display is at a minimum.
8. Disconnect the tuning function by pressing the CHAN buttons until the readout is 0. (During normal operation, CHAN must be set to 0 or acquisition is not allowed.) 9. Repeat the steps above for each channel on the system. For further information about probe installation and tuning, refer to the probe installation manual that shipped with your probe.
1. Start ProTune for either the experimental or walkup (account owner) interfaces as follows: Experimental Interface: a. Click on Acquisition on the main menu bar. b. Select Tune Probe … Walkup interface a. Click on Tools on the main menu bar. b. Select Tune Probe … The tune probe window opens. 2. Click on the button of the Nucleus to tune. 3. Select a criterion from the drop down menu next to Tune Criterion. Coarse – within 5 percent of optimum pw Medium – within 2 percent of optimum pw Fine – within 0.5 percent of optimum pw The criterion option is not shown for Walkup Operators unless the operator panel level is set greater than 30, see VnmrJ Installation and Administration for instructions on setting panel levels. 4. Click on Tune to Criterion button 5. Select the next nucleus and repeat step 2 through step 5 and continue with the next step when all desired tuning is completed. 6. Click on Close to exit the ProTune module.
Remote Tuning from the ProTune Window The ProTune interface window (shown above) can be used to tune the probe remotely. Functions and features of ProTune are shown. 1. Start ProTune by entering the following in the VnmrJ command line: protune('calibrate') The calibration files for the probe shown on the hardware bar of the VnmrJ interface, are loaded.
2. Click on the Refresh button. 3. After the ProTune window appears, make sure that the motor and sweep communication read OK before starting manual tuning. The ProTune window with rf reflection at 499.5 MHz is shown above. 4. Enter the frequency (MHz) in the Tune To box. 5. Click the Tune To button. The software reads the appropriate channel file and starts tuning. 6. Do the following to stop the automatic tuning and tune manually: a. Click the Abort Command button (might require several clicks) to stop. b. Enter the corresponding chan # of the desired turn frequency.
c. Click the appropriate CCW (counterclockwise) and CW (clockwise) buttons to adjust the tune and match. d. Enter a frequency in the Center box and click Refresh to update the reflection window to center the window. e. Enter a frequency width in the Span entry box and click Refresh to update the reflection window to set the window span. 7. Close the ProTune window — acquisition will stop automatically. Enter aa on the ProTune Window Description
Tuning a Probe with qtune This procedure describes how to use the qtune program to tune an NMR probe. 1. Set up the system for tuning: leave the thumb wheel switch on the TUNE INTERFACE set to observe mode, or 0. 2. Enter tn='n' su, where n is the nucleus to be tuned (e.g. tn='H1'). 3. Click the Probe button on the VnmrJ hardware bar. Enter an appropriate value for Tune gain (e.g., 50) and click Tune sweep. The Tune Display and Tune Control windows opens. The Tune Display is centered on the resonant frequency of the current experiment (sfrq). To change the gain and power values, click Exit in the Tune Control Panel and re-enter the qtune command with more appropriate values. 4. In the Display field, select Full or Minimal. • Full display shows the network-analyzer-like graph. • Minimal display simplifies the tune display by showing numerical values instead of the graph. When sweeping over a range of frequencies, the minimal display shows minimum reflected power and center frequency. When in CW mode, the minimal display shows the average reflected
5. In the Audio field, select On or Off. If set to On, a volume slider becomes available and a sound is generated that indicates how close the minimum reflection is to the center of the sweep window— the lower the pitch of the sound, the closer the minimum reflection is to the center. The sound immediately stops if the response lacks a discernible minimum reflection or if CW mode is set. To use the audio capability requires: • An audio speaker on the computer. • The probe tuned well enough so that a clearly discernible minimum reflection exists in the signal. • A range of frequencies sent to the probe (i.e, audio requires sweep mode rather than CW mode). 6. Place a marker on the resonant frequency and tune the probe as follows (this option is not available in minimal display): a. In the Tune Control Panel, click on the triangle next to one of the markers to open a pull-down menu. For more detail on using markers. b. In the menu, select the resonant frequency to tuning the probe. A marker corresponding to the selected frequency appears in the Tune Display window.
7. In the Tune Control Panel, type values as appropriate in the Span, Scale, and other fields on the Tune Control Panel. Using the dB scale usually facilitates probe tuning. 8. Adjust the tune and match capacitors while watching the Tune Display window. Use the match capacitor to increase the depth of the dip as much as possible. Use the tune capacitor to center the dip on the marker created in step 6. The dip displayed in the Tune Display window shows where little power is reflected at the frequency being observed. The depth of the peak shows the accuracy of the impedance matching of the probe coil to the transmitter and receiver. The horizontal location of the dip shows the frequency at which little power is reflected. The goal of probe tuning is to increase the depth of the peak (matching) while centering the dip at the desired frequency. 9. After the probe is tuned, click Exit. Begin the experiment. Selecting a Center Frequency The center frequency is the resonant frequency to which the probe is to be tuned. A list of center frequencies appears in the Center pull-down menu in the Tune Control Panel. Note that any frequency typed into the field will not be read until pressing Return. This applies to all text entry fields.
1. In the Center field, click on the triangle to open the pull-down menu, then select a frequency that equals or is close to the frequency the desired want. 2. Adjust the frequency by typing a new value in the Center field or by clicking the – and + buttons. The – or + buttons decrease or increase the value by the width of one span. If the center frequency is either typed in or changed by the – or + button, user is displayed next to the frequency. If the typed value happens to correspond to a nuclear frequency in the pull down menu, that nucleus is displayed. If the new center is too close to either of the system frequency limits, the span is decreased to allow the new center to be accepted, the message window will beep, and an error message will appear. If the specified center is past either frequency limit, the message window will beep, and an error message will appear. Adjusting the Span The span is the sweep width, in MHz, used in the Tune Display. 1. To decrease or increase the span to the next in the series 1,2,5 10,20, etc., in the Span field, enter a value or click the – or + button. Setting the span to less than 1000 Hz causes the message window to beep and an error message to appear. Setting the span to more than maximum span causes the message window to beep and an error message to appear. Setting the span to a value beyond the maximum or minimum frequencies causes the span to decrease, the message window to beep, and user warnings to appear. 2. In the Span field, click on the triangle to open the Span pull-down menu. • Select Last Span to return to the previous span value • Select Maximum Span to make the spectrometer sweep from the minimum to maximum allowable frequencies. • Select CW to temporarily stop frequency sweeping and to make the transmitter put out a CW signal. This sets the frequency to the currently selected center frequency. This mode is useful for checking the reflected power on the tune meter or for making other tests that require a fixed frequency.
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