Sound and Vibration
SCS 9005 - Vehicle Pass-By Noise certification and Cabin Noise
ass-by noise measurements ruled by noise standards, are approached experimentally by realizing Pass-by, Coast-by and in vehicle measurements of the sound pressure level. In most cases car manufacturers do not only want to check that the vehicle conforms or not to the regulations, they also desire to be able to analyse measurement results within the framework of research and development studies. The aim is to identify potential sources of noise: engine, power train, tire or airborne related and to reduce it. The simultaneous feature of pass-by and on-vehicle noise measurement would help a lot in performing those trouble shooting tasks.
The Pass-by test
Pass-by noise measurements ruled by noise standards, are approached experimentally by realizing Pass-by, Coast-by and in vehicle measurements (cabin noise) of the sound pressure level. The SCS 9005 dedicated system is built around “market available” Real Time analyzers with audio recording features and it becomes possible to use all analysis power to further post-processing recorded data. In most cases car manufacturers do not only want to check that the vehicle conforms or not to the regulations, they also desire to be able to analyze measurement results within the framework of research and development studies. The aim is to identify potential sources of noise: engine, power train, tire or airborne related and to reduce it. The simultaneous feature of pass-by and on-vehicle noise measurement would help a lot in performing those trouble shooting tasks. The SCS-9005 Version 4 system features a portable 4 to 16 channel Real Time Analyzer, a dedicated software and a full range of accessories to measure RPM, speed, position, centre line vehicle positioning, meteo conditions, others. The user interface is tailored to engineers need for fast testing and exhaustive data analysis.
ISO 362 standard defines the microphone positions as well as the length of the test run. In order to comply with the standard, the measurement must be carried out under certain conditions. These conditions are related to weather conditions (maximum wind…), back-ground noise conditions, and test surroundings (type of pavement…).
Microphones and Photocells
The two microphones are placed on both side of the test track at positions defined by the standard. The photocells and their reflectors are used to trigger the measurement. The measurement should be performed with the vehicle running consecutively in both directions (entering the test area from the left or from the right). For this reason, two sets of photocells are positioned at each end of the test zone.
The radar is used to track the position and speed of the vehicle. It allows the determination of the moment the car enters the zone defined by the standard (10 m away from the microphone). The radar used is a Doppler interferometer which gives equidistant pulses as the car is moving. Integration of these pulses will enable the precise positioning of the vehicle versus time. The instantaneous frequency of the pulses will enable the calculation of the speed of the car versus time.
The engine RPM as well as the throttle position are measured with on board sensors. They are conditioned in the vehicle and sent to the analysis system via telemetry. They are received by a remote antenna directly connected to the Pass-by signal conditioning unit.
Conditioning and analysis system
All the information are sent either via cables or telemetry to the test system. Signals are pre-processed by the SCS-5095 Front End and than fed to the 4 channel Real Time portable analyzer. Processed data are then transferred to a notebook using a rugged PCMCIA card. The analyzer and the notebook are battery powered, which is essential when performing outdoor measurements.
From analysis to report edition
The interest of test engineers is also to be able to understand the details of the analysis results by analysing each component of the frequency spectrum, and even to perform thorough analysis in the order domain for instance. The analysis system is a powerful development tool such as calculation of the frequency spectrum at each vehicle position for a detailed analysis of the problem. These results are automatically obtained at the end of the test while the vehicle is getting ready for the next passage. Proceeding this way, any eventual problem in the measurement can be detected right away and the measurement repeated, therefore saving a huge amount of time and money. Signals and results are saved and available for later analysis if desired. Analysis The signal is continuously acquired during the test. Once the car has passed, the analyser processes the data giving spectra at each vehicle positions. Report edition Report edition is often a critical point in the presentation of results. Report edition is therefore included in the Pass-by user interface and for convenience can be customized to every customer’s needs to meet with any company`s internal presentation requirements.
typical result from a Pass-by measurement is displayed below. The evolution of the sound pressure level as a function of the car position is displayed on the two top plots of the window. The maximum levels and their corresponding positions are automatically extracted and shown in the statistics window. One of the first noticeable points is that the maximum level for microphone 1 is measured when the car is at 7.50 meters from the start of the measurement zone, whereas the microphone will measure a maximum later, when the car reaches 9.18 meters. The second two plots represent the spectrum corresponding to a particular position for each microphone. The blue cursor (on the overall plot) enables to display the full spectrum for the car position of interest. The frequency information is not required by the standards but it will permit a deeper analysis of the problem. This point is essential for R&D investigations. Finally, a window represents the evolution of the RPM value and of the vehicle speed as a function of the car position.
Main characteristics of the system
• Automatic measurement according to ISO 362
• 1/3 octave analysis up to 20 kHz on 4 channels
• Audio signal recording on 4 parallel channels
• Automatic report of dBA level and spectra vs position or RPM
• FFT, 1/n analysis and order tracking
• Signal editing and post processing function
• Unique Centre Line control feature with on-board display
• Unique option for simultaneous pass-by and Cabin Noise measurement and analysis
• Portable and self contained
• 7 different parameters simultaneously recorded
• Real time WEB data transfer
• Radar and GPS positioning systems