Airbag Accelerometer Sensors/Aftermarket Bumpers

[TxDoc]

In the thread about what happens to your airbags when you add an aftermarket bumper, it got me interested in what happens, how it happens and why. So, I am making inquiries and will try to post it as I get it.  Feel free to add anything and the source here.

 

 The greatest demand for the micromachined accelerometer is in automotive air-bag systems.   In this application, the sensor is used to determine exactly when the bag should be deployed to prevent injury to a driver or passenger.   When an impact occurs, it results in vehicle deceleration, which is sensed by the accelerometer in the form of a change in voltage.   This fluctuation is monitored by electronic control unit, which sends a signal to trigger the air bag.

 

 The ADXL50 Accelerometer

 

Analog Devices' ADXL50 accelerometer, introduced in 1991 and in volume production by 1993, distinguished itself as the first commercially available device to employ surface micromachining. Other firsts of this truly breakthrough device include:

 

The first surface micromachined accelerometer to be manufactured in high volume

The first micromachined sensor with the motion sensor element, extensive signal conditioning circuitry and self-test circuitry on a single chip

The first micromachined sensor IC whose moving part moves in the plane of the chip

The first surface micromachined sensor

The first micromachined accelerometer sensor of its size

For the automotive industry, the $5 ADXL50 was revolutionary, supporting the monumental cost reductions in airbag electronics from several hundred dollars in 1990 to $30 in model year 1998. Its combination of high performance, reliability, small size, and low price made record-breaking waves in the industry with "single point sensing" in a low-cost, highly reliable airbag system.

 

The New ADXL150/250/202 - For More Than Airbags

 

While others were still working on their first commercial device, Analog Devices introduced the ADXL150 and ADXL250 during September 1996. Complete with added features, improved performance and reduced size, they are more general purpose devices than their famous predecessor. The ADXL150 now resolves signals as low as 10 mg, while still providing full-scale measurement to ±50 g. Zero g drift has been reduced by 90% to 0.4 g over the standard industrial temperature range, and power consumption has been reduced to just 1.8 mA per axis. The features of the ADXL150 and ADXL250 translate into a smaller, lower cost, higher performing motion sensing solution which will open the door for many new applications.

 

The ADXL250 delivers performance that is identical to the ADXL150, with one difference. It provides dual-axis sensing, allowing designers to sense motion in two planes, without doubling the cost - and space - of hardware. This is the first time two sensor elements have been integrated with signal conditioning onto a single chip. Both versions incorporate their own signal conditioning, clock generator, demodulator and timer.

 

Representing the next major leap in accelerometer technology, the ADXL202 provides a digital interface with microcontrollers and microprocessors. It is for automotive, industrial, and mass market consumer applications, such as video games and other high volume electronics. Low power operation from 3 V to +5 V also makes the ADXL202 optimal for battery-powered applications.

 

 

http://www-ee.eng.hawaii.edu/~cheol/class/ee626/image4MO.JPG

(I don't know how to make the above pic show up by itself)

a)mechanical ignition airbags fit inside the steering wheel pad. When a collision occurs, the inertial sensor moves, setting off a mechanical igniter and inflator to deploy the airbag. As the sensor and igniter were in the same unit, the compact airbag unit easily fit most steering wheels, allowing broad application of the airbag unit.

b)With electrical ignition airbags, a computer monitors signals from the impact sensor. When it detects a collision, the computer sets off the airbag's igniter electrically. Therefore, the sensor need not be close to the airbag, but can be placed anywhere on the vehicle and connected to the airbag with wiring. This is especially effective when fitting both driver- and passenger-side airbags.