Microprocessor based speed and position measurement system

An on-board speed and position measurement system capable of meeting the performance and stringent safety requirements of a short headway (3 s) automated transit system is presented. A Hall effect sensor, which senses the presence of teeth on a gear, is located at each wheel and provides an uncalibrated incremental measure of the distance traveled. Microprocessors are used to implement the calculations necessary to derive accurate measurements of centerline speed and position from the raw sensor data. A direct measurement of the time between sensor pulses is used to improve speed measurement accuracy. A combination of hardware redundancy and fault detection algorithms in the microprocessors is used to meet safety requirements. This allows use of the measurements by safety functions, such as the collision avoidance and overspeed protection systems, as well as by control system functions which are not safety-critical. Use of a single system to meet all on-board needs for speed and position measurements allows use of the integrated command and control system approach that is necessary to meet the performance requirements of short headway systems and avoid excessive costs and complexity.