Optimization of the contact material and conductive ink used for an automotive fuel level sensor

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Optimization of the contact material and conductive ink used for an automotive fuel level sensor

Ireland, H.W. / Smith, E.F.

The initial design for a potentiometric, automotive fuel level sensor utilized a copper alloy contact (C770) sliding against both the conductive silver and resistive ink. Because the service environment required immersion in both gasoline and gasoline vapors, the sensor utilized thick film technology on an alumina substrate. The initial combination resulted in either excessive noise at low gram loading or ink wear at high normal forces. A test program, simulating the in-tank service conditions, was undertaken to increase the cyclic lifetime of the senor. By increasing the Palladium content of the conductive trace, ink wear was eliminated. It was also necessary to change the layout of the thick film traces in such a way to eliminate sliding against the resistive ink. However, with these changes, contact wear was found slightly later in life. The contact wear is thought to be caused by residual glass components that remained near the surface after firing of the conductive ink. The introduction of a harder palladium based contact material allowed the use of lower normal loads and eliminated both the noise and the wear problems. The combination of the Pd based contact material and a high Pd content, conductive ink resulted in fuel level sensor capable of long life service under the aggressive conditions found in an automotive gas tank.