The application of embedded system in NMR spectrometer lock system

Homogeneous and stable magnetic field is essential for a high-resolution NMR spectrum, especially one which requires signal averaging or phase cycling. The field-frequency lock technique can effectively improve the long-term stability of the magnetic field. The whole design scheme of the lock system for NMR spectrometer is presented in this paper. The digital control is implemented with Xilinx Virtex-4 FPGA, XC4VFX12-FF668, the signal received from the probe is detected by the quadrature detector, and the resonance frequency drift is locked by the quasi-feedback loops. In the slave computer of the lock system, Wind River´s VxWorks real-time operating system is chosen to fulfill the strict requirement for the performance of real-time data acquisition and control, as well as the stability of operation system. Online debugging with the Varian 500 MHz spectrometer shows that the lock system achieves the goal of compensating for the intrinsic drift of a superconducting magnet field.