Abstract The magnetic field is one of the most important parameters in solar physics, and a polarimeter is the key device to measure the solar magnetic field. Liquid crystals based Stokes polarimeter is a novel technology, and will be applied for magnetic field measurement in the first space-based solar observatory satellite developed by China, Advanced Space-based Solar Observatory. However, the liquid crystals based Stokes polarimeter in space is not a mature technology. Therefore, it is of great scientific significance to study the control method and characteristics of the device. The retardation produced by a liquid crystal variable retarder is sensitive to the temperature, and the retardation changes 0.09° per 0.1° C. The error in polarization measurement caused by this change is 0.016, which affects the accuracy of magnetic field measurement. In order to ensure the stability of its performance, this paper proposes a high-precision temperature control system for liquid crystals based Stokes polarimeter in space. In order to optimize the structure design and temperature control system, the temperature field of liquid crystals based Stokes polarimeter is analyzed by the finite element method, and the influence of light on the temperature field of the liquid crystal variable retarder is analyzed theoretically. By analyzing the principle of high-precision temperature measurement in space, a high-precision temperature measurement circuit based on integrated operational amplifier, programmable amplifier and 12 bit A/D is designed, and a high-precision space temperature control system is developed by applying the integral separation PI temperature control algorithm and PWM driving heating films. The experimental results show that the effect of temperature control is accurate and stable, whenever the liquid crystals based Stokes polarimeter is either in the air or vacuum. The temperature stability is within ±0.015° C, which demonstrates greatly improved stability for the liquid crystals based Stokes polarimeter.
Keywords liquid crystals based Stokes polarimeter — high-precision temperature measurement — space high-precision temperature control — temperature field analysis — PID control
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