Designer's Corner 1278

Passenger position sensor

Automobile manufacturers offer switches to disable the passenger airbag when the seat is unoccupied or occupied with a child or infant seat. This proposed system detects passenger's size and position so that the airbag system can make its own decision about when to fire.

The system uses strain gauges to measure the bending force on two load-sensing beams under the seat. Four vertically oriented pins, attached to the beams, transmit force from the seat pan to sensor beams. This method of attachment provides an accurate vertical force measurement regardless of where the load is positioned on the seat.

By splitting the output of the forward and aft Wheatstone Bridge sensors, the system also detects tipping moments generated when a passenger sits on the edge of the seat--another situation where the airbag should stay put.

Bob Walker, Imperial Instruments
201 South Congress St.
Rushville, IL 62681
(217) 322-2912.

Bus-bar assembly

To keep fire truck subsystems operating during emergencies, Pierce Manufacturing, Appleton, WI, changed from hard wired controls for pumps, lighting, and hydraulics to a high-current, thread-mount, fork-connector, bus-bar assembly.

Placed in the cab's ceiling, the assembly includes six circuit boards and twelve AMP(R) fork connectors. Power is transferred from the bus bar to the circuit boards at 60A per fork connector.

Fork connectors attach with one piece of hardware. Tested at 200F and 10-g vibrations, these thread-mount forks sustain 500 cycles with less than a 1/10 millivolt drop.

Paul Glaser, AMP
21220 N. 19th Ave.
Phoenix, AZ 85027
(602) 581-5713.

IR spectrometer

The heart of this compact gas sensor is an integrated hollow-waveguide microspectrometer. Since a dual-beam principle looks at the absorption at the wavelength characteristic of CO₂, l = 4.23 mm, and a reference wavelength, l = 3.7 mm, gas concentration measurement is independent of light drifts.

Infrared (IR) light from a miniature tungsten lamp enters the spectrometer through the entrance slit and moves throughout the hollow waveguide, which contains the gas under study. A concave reflection grating focuses the light onto a two-element selenide detector on the emitting aperture. This detector is adjusted to the CO₂ and reference wavelength, so the intensity of both channels can be measured simultaneously.

Peter Zuska
American Laubscher Corp.
ALC Bldg, 80 Finn Ct.
Farmingdale, NY 11735
(516) 694-5900.