Chapter 2. CP/MAS Solids Operation
27
VNMR 6.1C User Guide: Solid-State NMR
01-999162-00 C0402
Using Air Flow to Set the Spin Speed
This procedure describes how to set the
air flow to spin the rotor. This mode of
operation is applicable when operating at
the extremes of the temperature range of
the probe.
1.
Enter
spinner
in the VNMR
input window to open the Spinner
Control window (see
2.
Click on the High speed spinner
(solids style) control button.
3.
Adjust the two slider bars to
zero.
4.
Click the Set spinner airflow
instead of speed.
5.
Click the Turn spinner off button.
6.
Adjust the bearing gas pressure to 30 psig for CP/MAS probes.
7.
Open the drive pressure regulator fully.
The rotor may initially spin when using older controllers but will stop when the
electro-pneumatic valve engages. The spinner is now in an unregulated mode in
which the airflow is set directly using the slider bar. The slider bar sets the DAC
value that controls the electro-pneumatic value. The DAC has a range of 0 (no air
flow) to 65536 (full open). Only the air flow is set there is no spin speed regulation.
8.
Set the slider bar at 2500.
9.
If the rotor fails to spin or no DAC reading appears on the tachometer, stop the rotor
and remove it from the probe, check the paint on the rotor and the tachometer cables.
Repeat this procedure beginning at step 1.
10. Adjust the slider bar until the rotor is spinning at the desired speed.
Move the slider bar slowly. If the rotor is spinning, changing the air flow in small
steps is good practice.
The fine slider bar (bottom) can be increased by one unit when the mouse pointer is
clicked in the bar. The speed displayed in the Acquisition Status window is correct.
The speed displayed pneumatics/tachometer box tends to be slower.
Do not let a sample rotor exceed the maximum rating for any of the rotor parts
during this process. Speed ratings may vary as a function of temperature and sample
density.
Using Drive and Bearing Pressure to Control Spin Speed
1.
Follow the setup instructions in
“Using Air Flow to Set the Spin Speed,” page 27
2.
Reduce the drive pressure until the rotor spinning as a result of the bearing air.
3.
Set the slider bars to their maximum position (electro-pneumatic valve is now fully
open).
4.
Adjust the drive pressure to achieve the desired rotor spin speed.
Figure 4. Spinner Speed Control Window