Vehicle Measurements


By order of Mercedes Benz the measurement specialist firm INDA consult, Ludwigsburg, Germany, examines acoustic implications on a vehicle body with the central point acoustical and psycho acoustical appliances. The is a very important member of the sound source detection system. Used as a front end it supports fast evaluation of the measured acoustic signals.

The customers of INDA consult are automotive companies and their suppliers. In addition projects in the areas of domestic products, commuter traffic, motorcycles and scooters are processed. Furthermore the company organizes three days seminars to train staffs in the areas acoustics and oscillation technology.

The commitment for the automotive industry is specialized to examinations for whole cars under real driving conditions and on test units. On engine test stands engine gearbox combinations are tested according to their acoustical and oscillating behavior. Structure examinations with whole cars, empty bodies, and other components are some of the other tasks like measuring the noise of cars passing by according to ISO 362. In the last four years INDA consult cooperated with Daimler Benz AG. As a part of the cars development the main project was the designing of the new M class. The Ludwigsburg firm did any of the acoustic and oscillation examinations for whole cars and empty bodies.


Physiological Correct Recording of Acoustical Events


Because the exact determination of sound sources was difficult with earlier measurement equipment INDA consult developed in cooperation with the research department of Daimler Benz a revolutionary new method to examine non stationary operation.

The so called SLS system (SLS = Sound Localization System) combines the statuary stipulated measurements in the second and the third gear according to ISO 326 (DB(A)) with microphone array data measured at the same time. The vibrations/oscillations measured with the microphones (sound signals) of a passing car were recorded with a TEAC RX-8032 recorder at first. For all actual and further measurement tasks with Mercedes cars the new TEAC recorder system GX-1 is used. The GX-1 is not run as a conventional recorder but as a front end respectively as an analog to digital converter. The analog oscillation signals of the ICP measurement microphones were digitized by the GX-1 and transferred over a SCSI interface to a Windows NT PC.

The managing director of INDA consult Elmar David says to the impressing advantages "because we use the GX-1 as a kind of bridge between the time data measured from the microphones to the data processing PC it is possible to make analyses and computations immediately". Furthermore the immediate processing in the field brings tremendous savings of time in contrast to the older system. Basically the GX-1 is equipped with eight slots (two channels per slot) where different signal conditioners (modules) can be installed according to the individual task: Conditioner for measurement microphones, charge amplifier, rotation or thermal conditioner, and amplifier for recordings with strain gages. With a recording time of two hours 14 channels with a bandwidth from DC to 40kHz, or 30 channels with a bandwidth from DC to 20kHz, and 64 channels with a bandwidth from DC to 10kHz can be realized (extension units). Any channel can be operated with up to 200 samples per second at 16 bit resolution. This means: Recordings up to 80kHz per channel are possible.


Connecting a Windows PC


The package of the GX-1 contains a 32 bit software tool which can be run under Windows 95 and Windows NT. It allows several adjustments like setting sample rates and trigger modes. In addition oscillation signals, time signals, and calibration values can be shown on the screen. Depending on the installed modules the functions of the conditioner can be visualized. The representation of the data is possible as line or as bar graphs.