Design Of PID-Based Units For NMR Spectrometers

NMR (Nuclear Magnetic Resonance) spectrometers, which are recognized as very important tools for research and analyzing, have got more and more attention. The variable-temperature and sample handling pneumatics system and the MAS controller are two essential parts to ensure the NMR experiments to be successful.Modern NMR spectrometers are always desired to be automatic and intelligent. Considering that PID (Proportional, Integral and Derivative) cybernetics are suffici--ent for many control problems and are found in large numbers in all industries, it is feasible to apply PID algorithm to the design of NMR spectrometers to provide fea--tures like automatic tuning, rapid response and continuous adaption. This paper pre-sented designs of the temperature and speed controllers based on PID. Hardware and software schemes and implementations are described particularly here.A variable-temperature and sample handling pneumatics system was designed to regulate the temperature and spinning. An ARM (Advanced RISC Machine) proc-essor with on-chip CAN bus interface is used to control the airflow and sample tem-perature through PID algorithm. Circularly measured difference between the setpoi--nt and the process variable is used to achieve a sum of three terms called P, I and D. Further, this design made an attempt at a variation of the basic PID to get a sectioned control structure that substantially improves its performance and operability.The design of a MAS controller is presented to meet the demand of solid NMR spectrometers. Double closed feedback loop is formed by both electrocircuit and the embedded programs. An STM32controller is used to run the PID algorithm, confi--gure IC chips, and communicate with the other subsystems. Both the speed and air press--ure are measured and managed to get control output. An automatic PID cont--roller tuning method is designed, which provides a stable of alternative parameters. After distinguishing the error field, given coefficients can be ascertain. It is forsee--able that control quality can be improved by gain scheduling and adaptive control.Test results proved that the designs presented in this paper are viable.In conclusion, suggestions are proposed.