Crash detection accelerometers

One requirement of crash-detection accelerometers is to provide a self-test feature. In one manifestation of this feature, a portion of the accelerometer is used to actuate the structure on demand. Fig. 7.1.12g shows an example of a lateral accelerometer from Motorola and the associated self-test actuation section of the design. In this case, the self-test actuates the structure to an equivalent 20 g (versus the 40 g range for the crash-detection application). Self-test is performed upon initial vehicle ignition turn-on to determine the health of the sensor before operation. 

Government safety regulations have been the compelling market driver for crash-detection accelerometers. Initially, mechanical sensors were used at several locations within the car to obtain the crash signal. The MEMS accelerometer enabled... 

Fig. 7.1.1 Automotive crash-detection accel- 21] on the left and the Bosch XL-lateral accelerometers a) Analog Devices ADXL50 [8, 9] erometer (courtesy Dr. Jiri Marek) on the right...

In developing these new algorithms, the requirements for sensors added more of them outside of the central control module for two reasons. First, some types of crash were difficult to detect within the short time frame required for deployment (such as offset pole crashes) and the solution was to provide a high-g precrash sensor within the front of the vehicle. And second, the need for side-impact detection required deployment decisions even faster that the frontal crashes (within approximately 5 ms). Both of these requirements moved accelerometers to satellite positions closer to the perimeter of the vehicle where they are more likely to pick up impacts from small objects. 

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