Error Analysis And Improvement Of Rail Longitudinal Force Measurement By Strain Electrical Measuring Method

Continuous welded rail is a long rail line which is welded by the standard length rails. Because its ends are completely fixed, it will produce a great longitudinal force when rail temperature changes to a large extent. The great force may cause rail buckling or breaking. which threaten running safety seriously. So accurate measurement of rail longitudinal force will be important for directing track maintenance and judging whether rail buckling and breaking happen.In the paper, based on the principles of the rail longitudinal force measurement by strain electrical measuring method, flake strain sensor and wireless strain acquisition node were adopted and connected according to half bridge circuit of compensatory approach. When the rail temperature changes, the rail strain which will not happen for the restriction will be measured in the project. And rail longitudinal force will be calculated from the measured strain. For further enhancing the measurement accuracy of rail longitudinal force, strain transmission error of flake strain sensor and temperature drift error of strain acquisition node were analyzed.According to the reason for the error of flake strain sensor, non-flake strain sensor was designed after structure improving and its manufacturing process was devised. Experimental results verified that it has the same measurement accuracy with strain gage. It protects the measurement from stiffness reinforcement effect of the flake, and eliminates the strain transmission error from the source. At the same time, its protecting process is still completed in the laboratory as flake strain sensor, and it keeps the advantage of operating simply and quickly in the measurement spot.According to the relationship between temperature drift error and the node temperature, transverse cubic spline interpolation and longitudinal piecewise linear interpolation algorithm were adopted, and software for temperature drift error compensation was written with Visual C++6.0. The compensation for temperature drift error of the wireless strain sensor node was realized. Experimental results showed that the temperature drift error were less than±10uε after the compensation within the temperature range of28~56°C. The temperature drift error was reduced more than75%using this compensation method, which significantly improves the measurement accuracy of the wireless strain sensor node. Finally, the measurement projects before and after improving were used to measure the rail longitudinal force at continuous welded rail and the measured data was compared. In the experiment, the maximum absolute error measured by the project before and after improving was224.6KN and65.9KN. and it was reduced70.7%after improvement. The average value of absolute error measured by the project before and after improving was79.9KN and23.7KN. and it was reduced70.3%after improvement. So the improved measurement project enhanced the measurement accuracy of rail longitudinal force significantly.