Conductor burnishing

#1. Field of the Invention

#This invention pertains generally to measuring and testing, and more particularly to measuring liquid levels using a float and sensor. The measuring apparatus is preferably used to detect fuel levels within a receptacle such as a fuel tank.

#2. Description of the Related Art

#FIG. 1 illustrates a prior art fuel sender, and FIG. 2 illustrates a greatly magnified conductor typical of the sender of FIG. 1. FIG. 3 illustrates the surface topography of the prior art conductor in comparison to an average thickness. FIG. 4 illustrates the burnishing process of the present invention, which yields an element illustrated by greatly magnified view in FIG. 5. FIG. 6 diagrams the basic manufacturing flow required to produce an element in accord with the present invention.

#The prior art surface topography is illustrated at 310 in FIG. 3. A number of peaks and valleys are found therein, some which are typically quite sharp or jagged. In contrast a smooth line 300 is illustrated which represents the average height of surface 310, and which would represent an exceptionally smooth surface. While in the prior art an average surface height 300 was specified, this in no way took into account the potentially widely varying heights or asperities in the surface. Asperities, the present inventors discovered, such as the differences between peaks represented by 133 in FIG. 2 and valleys represented by 131 in the same figure, designated by R.sub.a, and the relative sharpness of peaks 133, were discovered to rapidly erode contactor 140 to leave a sharp edge thereon. Once this degradation occurs, contactor 140 may actually act like a knife or wedge, cutting into and removing conductors such as conductor 120 from substrate 110.

#In the typical cermet process, glass binder is not melted but is instead sintered. Even if the glass were melted, an unreasonable time above the melting point would be required to smooth the surface thereof, due to the inherent high viscosity of molten glass. Furthermore, such an extended time which would be required for melting can, as in the case of Riley, result in a complete loss of exposed conductive particles. So, while the aforementioned prior art solutions improved secondary factors such as contactor undulation on a macroscopic scale as shown by line 150, the primary issue of surface roughness was not adequately addressed. Furthermore, other techniques such as firing multiple layers fail to fully address the issue, once again due to the elevated viscosity of a cermet composition during firing.

#In the present invention, a more direct approach is used to remove surface asperity, by directly burnishing surface 130. For the purposes of this disclosure, burnishing is defined as, "making smooth or glossy by or as if by rubbing; polish." In one embodiment, burnishing may be achieved by rubbing with a tool that serves especially to smooth or polish. In the preferred embodiment, a maroon colored general purpose abrasive pad available from 3M is wrapped on a drum 400. While the exact composition and construction of the abrasive pad of the preferred embodiment is not known to the inventors, the pad is a generally fibrous, open mat, unwoven polymer construction having abrasive content therein. Drum 400 is rotated and brought down into contact with surface 130. While drum 400 is illustrated for exemplary purposes, one of ordinary skill in the art will recognize that there are a multitude of methods available for burnishing and a multitude of tools suited for each of the methods.