Wheelset is one of the most important parts of the train, and the malfunction of the wheelset will directly affect the driving safety. Accurate and efficient wheelset geometric parameters detection is of great significance to the development of railway systems. Online measurement system using structured light is the current research hotspot, which has the advantages of non-contact, fast speed, etc. This paper proposes an in-field calibration method that is with simple operation, high efficiency and high precision for the on-line detection system. Position of the feature points was obtained with the accuracy of sub-pixel level. Considering two kinds of (radial and tangential distortion) distortions at the same time, the LM (Levenberg-Marquardt) optimization algorithm was used to obtain the nonlinear equations with the smallest comprehensive error. Then the internal and external parameters of the camera are obtained. In addition, the method has been applied to the site. High-precision result of wheel diameter which is obtained from on-line diameter inspection equipment can be used to correct the situation when the structure light deviates from the center of the circle. The field measurements show that the error of the wheel pair parameters using this algorithm is within 0.3 mm and has good repeatability.
The recent development of interband cascade lasers (ICLs) and quantum cascade lasers (QCLs) based trace gas
sensors enables the targeting of strong fundamental rotational-vibrational transitions in the mid-infrared, which are
one to two orders of magnitude more intense than transitions in the near-infrared. This has led to the development of
mid-infrared compact, field deployable sensors based on two sensor system platforms, laser absorption and
quartz enhanced spectroscopy. These sensor platforms are applicable for environmental monitoring, atmospheric
chemistry and for use in the petrochemical industry. The spectroscopic detection and monitoring of three molecular
species, methane (CH4), ethane (C2H6) , formaldehyde (H2CO)  and hydrogen sulphide (H2S)  will be
A near-infrared (NIR) dual-channel differential gas sensor system was experimentally demonstrated based on tunable laser absorption spectroscopy (TLAS) and wavelength modulation spectroscopy (WMS). The sensor consists of four modules, including distributed feedback (DFB) lasers for the detection of targeted gases, a custom portable DFB driver compatible for butterfly-packaged DFB lasers, a 20cm-long open-reflective gas-sensing probe and a custom costeffective lock-in amplifier for harmonic signal extraction. The optical and electrical modules were integrated into a standalone sensor system, which possesses advantages of user-friendly operation, good stability, small volume and low cost. With different DFB lasers, the sensor system can be used to detect different gases. Two DFB diode lasers with emission wavelengths of 1.65 μm and 1.53 μm were used to detect CH4 and C2H2, respectively. Standard CH4 and C2H2 samples were prepared and experiments were carried out to evaluate the performance of the two-gas TLAS sensor system. The relation between the second harmonic amplitudes (2f) and gas concentrations was obtained for the two gases by means of calibration. Both the detection error and the limit of detection (LoD) were determined experimentally. The sensor system will be useful in industrial trace gas monitoring due to its use of a low-loss optical fiber and an openreflective gas-sensing probe.