Precise Measurement Of Micro-displacement At Low Temperature

The coefficient of linear expansion is the inherent property of materials,which is embodied in the phenomenon that its volume changes accordingly when the temperature conditions change.When the pressure is constant,most substances show that when the temperature increases,the volume of substances will increase differently,and when the temperature decreases,the volume of substances will decrease differently.It is widely used in engineering.For example,in construction engineering,it is necessary to know the linear expansion coefficient of cement and take corresponding measures to prevent the extrusion of cement at high temperature.The linear expansion coefficient of parts in precision instruments and meters will have a greater impact,and the influence of the linear expansion coefficient of important engineering materials such as aerospace can not be ignored.With the development of society,the linear expansion coefficient of more and more materials has been discovered and applied to our life,but most of them are related to the material characteristics from normal temperature to high temperature environment.Because few work is carried out in low temperature environment,the linear expansion coefficient of materials at low temperature is rarely involved,but for aerospace,For the defense industry such as infrared guidance,the material characteristics at low temperature are indispensable.Therefore,a set of measuring device is designed in this paper to measure the expansion of materials at low temperature.The linear expansion coefficient of the pattern at this temperature is calculated according to the formula.The main research contents are as follows:(1)Select the sensor.Understand the basic principle of sensor measurement and select the sensor that meets the requirements.Before designing the device,find out the factors affecting the accuracy of measurement results and put forward corresponding preventive measures.(2)Built a stable low-temperature environment.Firstly,understand the current main refrigeration methods,and select the appropriate refrigerator according to the needs of the subject.Secondly,design the vacuum tank used in the main experimental sites,ensure the temperature uniformity of the measuring device by reducing three basic heat transfer methods,and check the strength of the vacuum tank with finite element software.Experiments show that the low temperature environment can be stably maintained to a low temperature of 70K.(3)Design measuring devices.Make rational use of material characteristics to ensure the accuracy of measurement results,such as using invar as the main frame to reduce the overall shrinkage of the device;The low thermal conductivity of G10 material is used to reduce the influence of external temperature on the measuring device.Use the micrometer as the adjusting mechanism to adjust the distance between the sample and the sensor.The error of the measuring device is analyzed,the error source is found out and the error is classified.According to the error transfer formula,the system error of the measuring device is only 0.38%and the accuracy is about 0.1 ?m.Meet the use requirements.(4)Experiment and data processing.Because the relative measurement method is adopted this time,it is proposed to eliminate the relative measurement error by replacing the sample with quartz of the same size.The least square method is used to fit the data.Compared with the standard data,the maximum error is 5.16%.