Varian UNITY INOVA NMR, Установка оборудования, Страница: 54 / 65

6.3 Testing CRAMPS NMR
01-999044-00 C0501 UNITY INOVA Solids Hardware Installation
53
Running the FLIPFLIP Pulse Sequence
1. Enter
flipflop
and set
d1=4 pw=1.5 fb=1e6 sw=2e6 np=128 tau=7
rof1=1.5 rof2=0
.
2. Set
phase1=0 phase2=0
(this sets up the “flipflip mode”)
phaser=0
phfid=0
or
'n' trig='n' gain=0 nt=1 dp='y'
.
Note that
trig='n'
is needed for UNITY INOVA systems since the 500-kHz synching
signal is not available and is unnecessary.
3. Acquire a FID and enter
df
to display both real and imaginary components. Adjust
the phase to minimize the imaginary signal. If this is not possible, check that the
signal is on resonance.
4. Enter
phaser=phfid phfid='n'
and reacquire. The imaginary channel
should be minimal. The real channel should show a FID pattern similar to that shown
in
Figure 24 .
5. Count the number of points in one cycle of the FID and the re-estimate the
pw
for a
90° pulse from the following relationship where
N
is the number of points in 1 cycle:
pw=pw*4/N
6. Repeat the acquisition, adjusting
pw
and then
tpwr
to get approximately a 1.5
µ
s
90° pulse.
7. Enter
gf
and then connect to the
acqi
window. Select FID and then IPA. Adjust
tpwrf
until a pattern similar that in Figure 25 is obtained. This occurs at the exact
90° pulse.
Running the FLIPFLOP Pulse Sequence
To run the FLIPFLOP pulse sequence rather that the FLIPFLIP pulse sequence, set
phase2=2
. This train of pulses alternately flips the spins into the XY plane—giving an
NMR signal—and back to the Z axis—giving no NMR signal. This sequence is used for
other adjustments in most CRAMPS/Multipulse spectrometers, but because of the phase
shifting circuit used in the
UNITY INOVA system, this sequence is only used to remove “phase
glitch” caused by asymmetric phase transients at the beginning and end of each pulse. The
resulting FID of the FLIPFLOP pulse sequence appears as a set of “tram tracks” as shown
in
Figure 26 .
Figure 23. Receiver Recovery FID