The present invention relates to the field of electric meters and, more particularly, to sensors utilized in metering devices.
Many electrical devices, such as electronic electric meters and induction or electronic type watt-hour meters for measuring electric power and usage, require current sensors for sensing the line current and producing an output signal related to the line current regardless of temperature.
Present sensor fabrication methods include electron beam welding of copper blades to nickel-copper resistors. While the prior art has been effective for many years, electron beam welding is not an economical means of fabricating sensors. Further, consistency of electron beam welding between different suppliers is difficult to maintain.
Previously, projection welding, and more specifically resistance projection welding, was not typically utilized when it was desired to bond a copper part to a copper nickel part. Copper traditionally does not withstand high pressures as is typically found with a projection welding. Further, when applying a projection welding technique to copper and copper alloy parts, the parts are heated to the liquid state. When the current ceases to flow through the parts, the parts can collapse while in the liquid state. Also, current sensors require consistent metallurgical bonding, as well as impedance consistency on each side of the conductors utilized within the current sensor. These characteristics are not attributable to projection welding due to the inconsistencies in the weld penetration.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by the present invention.
In an exemplary embodiment of the present invention, a method for resistance projection welding the components of a current sensor is disclosed. The method comprises the steps of providing a first blade having a projection extending outward and a first conductor, supporting the first blade and the first conductor, positioning the first blade adjacent to the first conductor so that the projection of the first blade contacts an opposed surface on the second member defining a contact area, supplying an electrical current of a predetermined magnitude and predetermined duration to the first blade and the first conductor to create a weld at the contact area and continually applying a compressing force of a predetermined magnitude to the first blade throughout the supplying step to resistance projection weld the first blade and the first conductor at the contact area.
The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following drawings and detailed description.