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playground:nmr
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playground:nmr [2021/04/01 11:11] carter |
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| - Set the FIELD SWEEP control to the optimum position. The optimum setting will be near 15 for the upper three ranges of the fluxmeter and near 5 for the lower three ranges. | - Set the FIELD SWEEP control to the optimum position. The optimum setting will be near 15 for the upper three ranges of the fluxmeter and near 5 for the lower three ranges. | ||
| - set the VERTICAL GAIN control for approximately 1/16-inch of "grass" on the face of the oscilloscope. | - set the VERTICAL GAIN control for approximately 1/16-inch of "grass" on the face of the oscilloscope. | ||
| - | - Now that the NMR is set to a frequency slightly lower than the desired frequency, we can begin slowly increasing the analyzer magnet control upward toward the current that will show a resonance on the NMR. Typical resonance patterns and control positions can be seen in the {{HVEC_NMR.pdf|Original HVEC NMR Manual}} figure 1. The resonance will enter the display from the right side and move across the CRT display from right to left. When the resonance is found and centered on the CRT display, the magnet flux (frequency) can be read on the Agilent counter located above the NMR Fluxmeter. Remember that because of magnet hysteresis and saturation effects, we can only increase the magnet current from this point on. If we decrease the magnet current we will have to recycle the magnet and start over for an accurate NMR flux value. | + | - Now that the NMR is set to a frequency slightly lower than the desired frequency, we can begin slowly increasing the analyzer magnet control upward toward the current that will show a resonance on the NMR. Typical resonance patterns and control positions can be seen in the {{HVEC_NMR.pdf|Original HVEC NMR Manual}} figure 1. The resonance will enter the display from the right side and move across the CRT display from right to left. When the resonance is found and centered on the CRT display, the magnet flux (frequency) can be read on the Agilent counter located above the NMR Fluxmeter. Remember that because of magnet hysteresis and saturation effects, we can only increase the magnet current from this point on. If we decrease the magnet current we will have to recycle the magnet and start over for an accurate NMR flux value. If you are moving up to a new NMR setting you can predict the new analyzer magnet current by the calculation (new magnet current = (new NMR / old NMR) * old analyzer current). |
| - The NMR Fluxmeter is a very sensitive instrument and you must proceed slowly when raising the analyzer magnet current or you can easily miss the resonance on the CRT. When the Analyzing Magnet computer control window is in the "ExtraFine" range, magnet at about 50 Amps and the FIELD SWEEP set at 5 gauss (these parameters will modify the the sensitivity) the resonance pattern will move completely across the CRT screen with a mouse movement of about 1/8 inch. Also, the same resonance movement will be obtained with about 20 clicks of the mouse button. On this range, one mouse click = 1 step of the stepping motor driving the NMR oscillator. | - The NMR Fluxmeter is a very sensitive instrument and you must proceed slowly when raising the analyzer magnet current or you can easily miss the resonance on the CRT. When the Analyzing Magnet computer control window is in the "ExtraFine" range, magnet at about 50 Amps and the FIELD SWEEP set at 5 gauss (these parameters will modify the the sensitivity) the resonance pattern will move completely across the CRT screen with a mouse movement of about 1/8 inch. Also, the same resonance movement will be obtained with about 20 clicks of the mouse button. On this range, one mouse click = 1 step of the stepping motor driving the NMR oscillator. | ||
| - Once the resonance is found on the CRT, slowly advance the magnet and NMR frequency by alternately increase the magnet a few clicks then raise the NMR frequency by issuing the command "up #steps" in the yellow tandem window, for example, in the analyzer current control window click the right mouse button until the resonance pattern moves to the left side of the CRT (about 10 clicks) then issue the command "up 10" in the yellow tandem computer window. This should move the resonance back near the center of the CRT. This process takes some practice but you will soon get used to the sensitivities of the magnet and NMR and you can slowly move the magnet current up until the desired NMR frequency is obtained. Once you are close to the desired frequency, you cam move the resonance to the center of the CRT with the VERNIER control and then read the exact NMR frequency on the counter. | - Once the resonance is found on the CRT, slowly advance the magnet and NMR frequency by alternately increase the magnet a few clicks then raise the NMR frequency by issuing the command "up #steps" in the yellow tandem window, for example, in the analyzer current control window click the right mouse button until the resonance pattern moves to the left side of the CRT (about 10 clicks) then issue the command "up 10" in the yellow tandem computer window. This should move the resonance back near the center of the CRT. This process takes some practice but you will soon get used to the sensitivities of the magnet and NMR and you can slowly move the magnet current up until the desired NMR frequency is obtained. Once you are close to the desired frequency, you cam move the resonance to the center of the CRT with the VERNIER control and then read the exact NMR frequency on the counter. | ||
playground/nmr.txt ยท Last modified: 2023/05/08 10:42 by carter
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