Patent ID: 8203339

Claim:
A nuclear magnetic resonance (NMR) spectrometer comprising a magnetic field generator for generating a magnetic field of a predetermined orientation, a rotatable mechanism, having a rotational axis, which comprises a stator supporting a rotor, the rotor being adapted to hold a sample to be tested by the spectrometer by being rotated within the magnetic field, and a device for determining an angle between the stator and the magnetic field, the stator being provided at a location that, in use, is within a region of the magnetic field having the predetermined orientation generated by the generator, the device comprising a Hall Effect sensor which is mounted with respect to the stator, the Hall Effect sensor being mounted at a known fixed angle with respect to the rotational axis of the rotatable mechanism, wherein the plane of the Hall Effect sensor is oriented so as to be at an angle of no more than 5° with respect to the region of the magnetic field that passes, in use, through the Hall Effect sensor, and the device further comprises a voltage measuring apparatus connected to the Hall Effect sensor for measuring the Hall voltage of the Hall Effect sensor and an angle calculating device, for calculating an angle of the stator with respect to the magnetic field, based on a measured value of the Hall voltage, and the spectrometer further comprising a system for adjusting the angle of the stator and the magnetic field in response to an output of the Hall Effect sensor.