Error Analysis And Improvement Of Monitoring Continuous Welded Rail Stress-free Temperature By Strain-Temperature Measurement Method

Continuous welded rail(CWR) is a long rail line which is welded by several standard cell rails together and is the track structure of the current high-speed railway. It will produce internal longitudinal force in CWR when the temperature changes. This may cause stress concentration or deformation in CWR. CWR stress-free temperature refers to the temperature corresponding to the zero CWR internal stress, and is one of the important indicators for judging security status of CWR according to Railway Standard. The change of CWR stress-free temperature indicates that the CWR is not constrained completely, resulting in excess stress or strain in addition to temperature stress in the CWR. Monitoring CWR stress-free temperature can help to detect anomalies in time and guide the railway workers to repair and maintain the CWR targeted. It plays an important role in the safe and stable operation of the high-speed railway.In the paper, temperature-compensated strain gages and compensation block method are used to measure the constrained strain of the rail. Temperature sensor is used to measure the rail temperature. The CWR stress-free temperature is solved by the constrained strain and the temperature of the rail at last, based on the principle of the strain-temperature method to measure CWR stress-free temperature.To further improve the accuracy of the CWR stress-free temperature measurement by strain-temperature measurement method, the reason of the compensation block falling off and the stain gage flaking and temperature sensor failure in the previous CWR stress-free temperature measurement program is analyzed. Then the installment and the layout of the sensors are improved. A new method in which the compensation block is separated from the working strain gages is proposed. Compensation block is pre-integrated in the measurement unit in the laboratory and its temperature is kept consistent with the rail by the thermal plastic and the thermal grease. As a result, the possibility of the compensation block falling off and temperature sensors failure is significant reduced.The strain gauge position deviation and angle deviation when pasted on the rail affects the measurement accuracy of the CWR stress-free temperature. So a scribing apparatus is designed and the strain gauge deflection angle error is reduced. Rapid, accurate positioning when pasting the gauge and installing measurement unit is realized.For a number of errors affecting the measurement results during monitoring CWR stress-free temperature by strain-temperature method, the quality of the sensors and the measurement unit is tested during integration and the technical requirements are proposed to ensure good performance in the application next. The test items include time drift. temperature drift error, vibration resistance, analog measurement of the CWR stress-free temperature and temperature hysteresis effect.To reduce the temperature drift error in the process of monitoring CWR stress-free temperature by strain-temperature method, the full-bridge method instead of the half-bridge, software compensation method after measuring the temperature drift by a certain material and the bridge arm resistance screening methods are attempted respectively. Experiment shows that the temperature drift error is reduced to varying degrees by the three methods.Finally, the improved scheme is implemented to monitor the stress-free temperature in a typical operating CWR. Result shows that the measured CWR stress-free temperature range measured by the improved scheme meets the safety and stability condition of the CWR according to the railroad standards.