Implementation of a GPS based Pass-By Measurement System

This paper describes an innovative pass-by system specifically developed to fulfil the Standard requirements. Such device runs on a highly flexible platform system, open to the various needs of the NVH field thanks to its design and software modularity. Differently from other pass-by systems, it is based on a GPS receiver able to track both the vehicle position and its speed at a rate of twenty times per second. All the test parameters are fully selectable and the driver can interact directly with the application software installed on a small and light PC. Since the system is GPS operating, there is no need to use any radar or lightbarrier. The in-vehicle module acts as an interface for the driver and gathers several kinds of data: vehicle position and speed, engine temperature and engine RPM and throttle position. In the meantime, the Ground Station collects all the information about the acoustical parameters with an audio and video stream of the pass-by test. A bi-directional high transfer rate data connection via Wireless LAN is established between the in-vehicle unit and the ground base station, allowing real time data transfer of the main parameters. All the information can be displayed both on the pilot screen and, at the same time, on the base station PC. The acoustic measurements are performed by using a multi channel acquisition system. Each channel of the instrument can measure, in parallel and in real time, SLM values, FFT and 1/3 octave analysis. At the end of the test, the main acoustical data and the GPS quality parameters are shown to the driver, who can decide whether to accept the measurement session or reject it. The driver can also decide to store the car paths together with the sound pressure level time history and the overall acoustic data of each session for further post processing.