Fabrication of reference standard 1 ohm resistors from Evanohm S alloy

The fabrication of reference-standard 1- Omega resistors that have characteristics superior to those of the Thomas-type resistor is described. A coil of Evanohm S wire was fabricated into a four-terminal resistor. A program of heat soaking at temperatures below 500 degrees C for varying periods brings the first-order temperature coefficient and the resistance correction at room temperature close to zero. Resistance adjustments are made using an electrolytic etching technique to achieve the required specifications. The heat-treatment program also achieves a low initial drift rate. The finished coil is fitted into a mount incorporating three hinges that support the coil without detracting from its performance.<>