Ford Motor Company Limited

Jon Tourville

Christopher J Kemp

A circuit for determining the operability an airbag squib resistor. The circuit includes a current source, the squib resistor to be measured, a first resistor whose resistance is equal to the minimum acceptable resistance of the squib resistor, a second resistor whose resistance is equal to the maximum acceptable resistance of the squib resistor, a voltage-to-current converter, a capacitor, a comparator, and a microprocessor with a counter. A first switch connects the squib resistor and first and second resistors in series. A second switch couples the inputs of the voltage-to-current converter individually across the squib resistor and first and second resistors. As the second switch is coupled to the squib resistor, the first resistor or second resistor, a third switch is opened to initiate charging of the capacitor which is coupled to the output of the voltage-to-current converter. A time measurement is made of the time required for the capacitor to charge to a predetermined threshold voltage. The time measurement is made with the second switch in each of its three states. The time measurements are compared and the squib resistor is deemed inoperative if the time measurement for the squib resistor is not within the range established by the time measurements for the first resistor and the second resistor.

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Colorado Springs, CO, United States of America

Jon Tourville