| The Superconducting gravimeter is an excellent relative gravity instrument for performing temporal gravity measurements due to its high resolution and stability.Since the advent of superconducting gravimeter,its development has been monopolized by the GWR company in America.To realize the autonomous controllability of high-precision instruments,our group has carried out the development of a superconducting gravimeter(SG),which has been developed to the engineering prototype stage.The internal temperature fluctuation noise is the dominant factor that limits the practical application progress of SG.Accurate temperature control is a key factor to suppress the noise.Therefore,in this thesis,a highprecision temperature control system is studied to provide technical support for the suppression of temperature fluctuation noise of SG.This accelerates the application progress of superconducting gravimeters in China.The demand index of the temperature control system is proposed for the model of temperature fluctuation noise of SG,i.e.in the time domain,the temperature control level should be ±10 μK under 0.1 μGal acceleration resolution within 24 hours when the instrument’s intrinsic frequency is 4 Hz.Based on this,a temperature control scheme is proposed based on the non-equilibrium AC bridge temperature sensing circuit and the PID feedback control closed loop.The influence of each parameter on the function and performance of the temperature control system is analyzed in detail.A noise model is established,and the feasibility simulation analysis is given.Then,the temperature control system is fabricated and tested.The temperature control system is constructed and verified for temperature measurement as well as temperature control functions by relying on stored Dewars.The results show that the correlation coefficient between the self-researched temperature measurement system and the commercial thermometer reaches 99.8%,and the scale factor is about 66 V/K;the temperature fluctuation residuals in the temperature control region can be stabilized at ±10 μK for a long time,and the commercial thermometer placed in the temperature control region reaches its resolution limit of ±100 μK.A solution for suppressing of ambient temperature effect is proposed.For a highprecision low-temperature measurement system,the readout circuit has an ambient temperature fluctuation effect at the ambient temperature end,which influences the test resolution of the low-temperature 10 μK.According to the temperature error model of the ambient temperature circuit,a scheme for matching the temperature coefficients of circuit components is proposed,and the scheme is analyzed and verified.The temperature coefficients of individual components are tested by the temperature modulation method,and then the selection,matching,and board soldering are performed.Using the same method,the temperature effects of the ambient temperature readout circuits of two temperature measurement systems with and without temperature coefficient matching are tested.The results show that the system with temperature coefficient matching is 50 times more resistant to ambient temperature fluctuations than the unmatched system.The temperature control system is integrated into our superconducting gravimeter.SQUID will unlocked due to electromagnetic interference,so it is verified that the temperature control system will not interfere with the SQUID test system before integration.After integrating,the temperature control system was tested,and its temperature measurement and control functions were normal.The temperature control results show that the residuals of long-time temperature fluctuations can be stabilized at ±5 μK in the time domain.This is much lower than the temperature fluctuations of the commercial thermometer with ±100 μK.The noise level of the commercial thermometer in the frequency domain is 50μK/√Hz@0.001 Hz,and the noise level of the residuals of the self-developed temperature control system is 5 μK/√Hz@0.001 Hz.The temperature control system becomes unstable when the temperature fluctuation of the external liquid helium pool exceeds 10 m K.It points out the direction for subsequent improvement of the practicality of the temperature control system in SG. |
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