Investigating inertial measurements using MEMS devices in trainborne automatic track condition monitoring applications

The majority of train-borne automatic track condition monitoring systems in operation throughout the UK rail infrastructure incorporate some form of inertial measurement unit. The rate gyroscopes and accelerometers which make up these units tend to be high value, relatively large and sometimes difficult to acquire. This paper explores the possibility of substituting readily available MEMS sensors into existing systems, initially in order to reduce support costs and improve spares availability. It is imagined that a miniature MEMS based IMU with multiple redundant sensors can be created in the long-term. Inertial measurements in the vertical profile are selected as the basis for a trial between a candidate MEMS device and the standard fitment accelerometer. The specifications of the measurement system are used to determine the minimum performance requirements of the replacement accelerometer. A suitable device is sourced and interfaced with the measurement system by means of a low noise two-stage noninverting operational amplifier circuit. Trial data is collected from the same four mile section of track, recorded repeatedly at constant speeds between 20mph and 90mph in 10mph intervals, and the data is then analysed graphically and statistically in order to determine the level of agreement between the two sensor types. The trial MEMS accelerometer is proven theoretically to be suitable for use with the current measurement system down to speeds of 25mph. The practical trial suffered from a compromised installation position but still proved that the MEMS accelerometer shows good agreement with the force-balance servo accelerometer, particularly at speeds above 50mph. The data suggests that a further trial with improved installation position would be worth pursuing.