4.4 Spinning the rotor under manual control
Prepare the pneumatic unit for operation by setting the proper probe parameters such as rotor size (BL4), magnet (SB) and rotor material (e.g. ZrO 2 ). Consult the manual for the pneumatic unit and/or section 4.4 of this manual.
For manual operation of the MAS pneumatic unit, set the unit in the local mode by pressing the local/remote button on the keypad of the pneumatic unit. Choose either manual or automatic for spinning control (see below).
It is also possible to operate the pneumatic unit from your host computer. For this, please refer to the XWINNMR manual and section 4.5.
Inserting the rotor
In order to make sure that the rotor will properly drop into the stator press the eject button on the pneumatic unit first. This will set the stator into a vertical position and ensure that a rotor which might be inside the probe will be ejected. After the eject air is on (and after removal of a rotor which has been in the probe) press stop. Then the packed rotor can be dropped into the probe via the transfer tube with the cap up. Close the insert tube and press the button insert on the pneumatic unit. This will automatically set the stator into the magic angle position after 10 seconds, if the pneumatic unit is operated in automatic mode. In manual mode you have to press the stop button again.
Spinning the sample
If the pneumatic unit is set to operate in automatic mode, you may start spinning the sample by setting the desired spin rate (Vd) and pressing the go button on the control panel. In case the rotor does not reach the desired spin rate in automatic mode, the rotor has to be spun up in manual mode.
For spinning up 4 mm Zirconia rotors in automatic mode, set the start bearing pressure to about 800 mbar, the default setting of 2000 mbar is too much for most samples. This can be done by pressing the bearing button in automatic mode and reducing the displayed Bp start to the desired value.
For manual spinning of the 4 mm Zirconia rotors use 800 mbar bearing (Bp) and 150 mbar drive pressure (Dp) to obtain a spin rate above 2.5 kHz. If the spinning rate achieved at these pressures is lower, slowly decrease BP to 100 mbar and immediately increase BP as soon as the rotor accelerates. Standard samples will easily spin in a 4 mm system, problems can be encountered for conductive materials or very heavy solid samples.
Stopping sample spinning
In automatic as well as in manual operation the rotation can be stopped by pressing the stop button. If you want to stop rotation manually from the keypad, decrease the drive pressure (Dp) first, and then lower the bearing pressure (Bp) slowly.
In order to stop spinning after variable temperature experiments, make sure that the heater is off and that gas of ambient temperature is used for the bearing!
Sample Ejection
After the rotor has stopped press the eject button on the pneumatic unit. The stator will switch back to the vertical position and the rotor be ejected. For this procedure the eject air pressure has to be adjusted by a little adjust knob on the rear of the pneumatic unit such that the pressure is high enough for the rotor to lift off, but not too high, such that the cap is not damaged when the rotor knocks against the closure of the transfer tube.