Page 39

EETE SEPTEMBER 2012

the need for change was further underlined as child booster car seats and rear-facing baby/infant car seats started to ap- FIR performance considerations pear on the market, as this raised concerns about how these For a FIr-based Ocs mechanism a wide dynamic range is not would be affected by airbag deployment. Therefore there is needed, the sensor array just has to cover -40 ⁰C to 85 ⁰C. The now a trend towards more sophisticated classification systems, optical resolution is not too demanding either, as the passen- often utilizing opto-electronic technology. ger’s position will be in a known area. the thermal resolution is far more important though - this needs to be in the ±0.25 ⁰K any Ocs solution that uses opto-electronic sensing needs to range. It is important that the heat effect of sunlight entering the be in the line of sight of the area of interest (i.e. somewhere that vehicle cabin is taken into account. to do this it is necessary to the view of where the passenger is situated is not obstructed). cut off the visible light spectra and near infrared (NIR) spectra The field of view (FoV) requirements are relatively con- using an optical filter, so that these do not interfere in any way strained, with 40 ºx10 º normally being more than enough. The with the sensor. sensor should have a reasonably low ing range in the region of one meter. POWEREfficient-hese criteria do not really poset frame rate of 4 Hz to 8 Hz, with a sens when studying the system at a more SOLUTIONS major technological difficulties, but detailed level, difficulties begin to surface if opto-electronically activated from the wall to the point of load TM Ocs arrangements use the visible part of the spectrum as their sensing media. several notable drawbacks are associ- ated with following this strategy. Problems with OCS using visible light there are of course day/night light level variations when visible light is used for Ocs sensing mechanisms, which call for active cabin illumination to be 10W~400 W included (this is normally placed on the inside of the car’s roof or on the front console). hats, long hair, beards, bright Digital Power Modules colored items clothing, etc, can all Intermediate Bus l Point of Load have a detrimental effect on the optical classification process too. As a result the accuracy of such sensor technol- ogy and its exposure to anomalies is a 0.25 W~600 W major concern. visible sensing systems require a relatively costly microcontroller Dc-Dc Converters unit (Mcu) as the processing power Board Mount l Chassis Mount involved will be fairly high. use of thermal far infrared (FIr) technology, working in the wavelength range from 5 µm to 15 µm, is becoming increasingly of interest in automotive 1W~2400 W passenger occupancy classification ap- plications. One of the great advantages Ac-Dc Power Supplies of a FIr imaging system is that, as it Open Frame l Chassis Mount l External detects radiated heat at the frequen- cies which the human body emits, it is much better at differentiating inani- mate objects from a real passenger. this methodology is not ambient light dependent, so there is no performance With a continuous focus oneffi ciency, density, andsystem optimization, difference between day or night opera- we keep our customers on theleading-edge of the power curve. tion. the need for active cabin lighting is thus dispensed with. Furthermore, considerably less processing power needs to be devoted towards it. these last two points make the overall system complexity and cost far lower. www.cui.com/power www.electronics-eetimes.com Electronic Engineering Times Europe September 2012 31


EETE SEPTEMBER 2012
To see the actual publication please follow the link above