Varian UNITY INOVA NMR, Hardware Installation, Page: 23 / 65

Chapter 3. CP/MAS Solids Module Installation
22
UNITY
INOVA Solids Hardware Installation 01-999044-00 C0501
Refer to the User Guide: Solid-State NMR for solids operating instructions and sample
preparation procedures. Refer to the manual NMR Probes Installation for information
specific to CP/MAS probes.
The fine attenuators are controlled by
dpwrf
or, in the XPOLAR pulse sequence by,
level1f
and
level2f
, which range from 0 too 4095 (where 4095 is the maximum). The
parameter
dpwr
has a maximum value set at 49;
level1
and
level2
have maximum
values of 63. The observe fine attenuator is controlled by
tpwrf
in the range 0 to 4095.
The maximum value for
dpwr
can be set in the
config
program, using the “Attenuator”
and “Upper Limit” labels.
You may have to create the parameters for fine control; for example,
create(parameter_name,'integer')
setlimit(parameter_name,4095,0,1)
.
tpwrf
can be created similarly.
3.2 Testing the CP/MAS Solids System
The CP/MAS Solids Module for Varian NMR spectrometers is used to acquire NMR data
from solid samples. The sample, usually a powder, is packed into a hollow rotor. The rotor
is placed in the probe at the “magic angle” of 54.7° from the magnetic field and spun at a
variety of speeds of up to 24 kHz. High-speed spinning at the magic angle, coupled with
high power decoupling, narrows the broad lines that are characteristic of solid samples
(typically 20 kHz) to about 1 ppm.
CAUTION:
Read this before doing any tests:
1. Run all tests with the XPOLAR pulse sequence and dm='nny' to
provide some protection to the probe from excessive decoupler duty
cycle.
2. Do not turn on the 100 W amplifier unless the output is connected to a
properly tuned probe (with a high-pass filter at J6003), to a large 50-
ohm load, or to a large 30-dB attenuator terminated in 50 ohms.
Refer to the manual NMR Probes Installation for tuning the decoupler and observe
channels on the probe. The probe must be installed and tuned before you can run a CP/MAS
solids experiment.
WARNING:
Dangerous high rf voltages exit that can cause serious injury or death.
Avoid electric shock by completely turning off the rf and
disconnecting rf cables before removing the probe.
Testing the Amplifier
Typical power outputs are given as a guide to troubleshooting. Pulse droop should be
recorded on all systems, but accurate power measurements are only needed if the system
fails to make pulse width or
γ
B
2
specifications. Power measurements should be made
through a 30-dB, 100-W attenuator on an oscilloscope or spectrum analyzer. A spectrum
analyzer provides more accurate power measurements.
1. Check the observe amplifier (Channel B) as follows:
a. Enter
rt('/vnmr/tests/hmb')
to recall parameters.
b. Enter
xpol='y' p2=1e4 at=0.01 d1=.05 nt=1e6 level1=63
level1f=4095
to set up for rapid pulsing.
c. Attach the observe cable from the magnet leg to a large 30-dB attenuator.
Attach the output of the attenuator to a oscilloscope or spectrum analyzer.