Development of Precise Temperature Control System for Solar Magnetism and the Activity Telescope

Birefringent filters are the key optical components of solar telescopes. The birefringence of the refracted crystal in the filter is very sensitive to temperature changes. The stabilization accuracy must be better than 0.01℃ to ensure that the filter operates stably and accurately. The high precision temperature control system of solar telescope has always been recognized as the core technology in the world, because of the complex structure of birefringent filter which is used outdoors. Temperature control system based on integral separation PI and feedforward is designed for the temperature control of the filter of Solar Magnetism and the Activity Telescope to achieve thermostatic control of the filter with High-Precision. High-Precision temperature acquisition is realized by using 24-bit AD and temperature measurement accuracy is improved by digital filtering algorithm. A compound control algorithm is designed by combining integral separated PI temperature control algorithm with a feedforward control that takes the ambient temperature as a parameter. Compared with the original filter temperature control system, this design greatly simplifies the system without loss of temperature control accuracy. As a result, PWM control strategy is output to achieve the secondary temperature control of the filter core and the insulation layer. The system had been tested for 72 hours in laboratory. When the temperature is set at 42.216 ℃, the accuracy of temperature control is better than 42.216+/-0.001 ℃. Since 2018, the system has been put into use at Huairou Solar Observing Station, and the maximum temperature fluctuation is 0.0075 ℃. The control system is accurate and stable, and a large number of high-quality scientific data are obtained.