Research on the LN2 auto-filling system for dewar vessel based on Bang-Bang + PID control

An automatic liquid nitrogen (LN2) filling system is described. In the process of LN2 automatic filling applied in the cooling of the CCD camera applied in the Large Sky Area Multi Object Fiber Spectroscopic Telescope(LAMOST) there exist problems such as imprecise system model, time varying parameter and stronger interference from the load, which result in the overflow of LN2 or insufficient amount of LN2 in the automatic filling of the Dewar vessel. To solve the above problems, a new method of low power heating of the sensors is adopted. The control electromagnetic valve through Bang-Bang control, and PID algorithm for heating are used. Experiments on the spot indicate the above combined control has solved the described problems to make sure the LN2 through automatic filling meets the requirements for astronomical observation and that the LAMOST operates in a stable and reliable way.