Temperature Effect Analysis Of The Backup Structure Of The Tianma Telescope

The Tianma telescope(TM65m)is a fully movable parabolic antenna structure.The backup structure(BUS)used to support the antenna reflection panel is complex.The pointing accuracy and surface shape accuracy of the antenna are sensitive to the temperature effect of the BUS.Therefore,it is necessary to study the temperature field of the BUS to provide data for further analysis of the temperature effect of the BUS.In this study,the TM65 m is taken as the research object,and the temperature distribution law of antenna BUS is analyzed by combining theory with experiment.The main research work is as follows :(1)infrared temperature measurement system In order to obtain as much node temperature as possible on the BUS,the infrared temperature measurement system is constructed based on the original temperature sensor temperature measurement system.The system has the advantages of non-contact measurement,fast response speed and wide measurement range,but the disadvantage is that the measurement accuracy is low,which is greatly affected by environmental temperature,surface emissivity of the measured object,measurement distance and angle of view.In view of the characteristics that the antenna BUS is curved surface,with the high-precision temperature sensor as the reference,based on the principle of infrared temperature measurement,the influence of measurement distance and angle of view on the measurement accuracy is mainly studied,and the correction model of the fourth-order and third-order polynomial of angle chord is established.The coefficient matrix of the polynomial is fitted by the least square method.At the same time,in view of the influence of environmental temperature on the accuracy of temperature measurement,through the statistical analysis of the environmental temperature data measured at the TM65 m site,the environmental temperature parameters in the temperature measurement system are adjusted to be consistent with the real environmental temperature or close to the average environmental temperature in the same period of previous years.In view of the influence of emissivity,through comparative experiments,a more accurate surface emissivity of the BUS is obtained.After parameter setting and error compensation,the infrared temperature measurement accuracy can be maintained within ±0.5°C.In addition,the control strategy is formulated and the program is compiled to ensure that the cloud platform installed with infrared thermal imager changes with the antenna elevation angle,and the temperature field of about one third of the continuous distribution nodes in the backup structure under different elevation angles is obtained,which provides a standard for subsequent verification of interpolation reliability.(2)reconstruct the temperature field According to the characteristics of the antenna back structure,the inverse distance weighted interpolation method is selected to reconstruct the temperature field of the back structure.Infrared temperature measurement and temperature sensor temperature measurement as standard temperature measurement.By comparing the root mean square error(RMS)between the interpolation temperature and the standard temperature at different distances k in the interpolation function,the inverse distance power k in the weight function of the interpolation method is determined.On this basis,the temperature field of the overall BUS is reconstructed by using the inverse distance weighted interpolation method.After analyzing the RMS of partial temperature and standard temperature in the temperature field,it can be seen that the temperature field of the BUS reconstructed by using the inverse distance weighted interpolation method is reliable.Through the statistical analysis of the temperature distribution of the chord on the BUS under various working conditions,it can be concluded that the temperature level of the antenna BUS is closely related to the solar azimuth angle,height angle,wind speed,antenna pitch angle and azimuth angle.The analysis results provide a good reference value for the subsequent temperature effect analysis of the BUS.(3)pointing error and focal length error the temperature field of the BUS obtained by interpolation reconstruction is used to calculate the temperature difference in the height direction,diameter direction and radius direction of the BUS,and then the pointing error and focal length error of the antenna are calculated.It provides a reference for the subsequent antenna pointing correction and focal length correction.