TABLE OF CONTENTS The introduction of ever more sophisticated electronic measurement and data transmission systems in the 1960s for use in industrial, military, communications, and scientific applications has resulted in the increasing use of precision resistors. The performance of these components is generally two or three orders of magnitude greater than that of conventional resistors. For example, proper operation of a 20-bit analog-digital converter requires the use of resistors with ohmic values between 1,000 and 100,000 ?, tolerances of approximately 0.005% between resistors, TCR of 2 ppm/ C, and operating drift of less than 150 ppm at 125 C and 10,000 hours of operation.
It is easy to see how the development and fabrication of such components introduced requirements that were quite different from those for resistors used in less critical applications. More stringent requirements led to the development of new resistor technologies for wirewound resistors, resistive film, foil materials deposited or glued on rigid substrates, and thin films deposited on substrates and etched to create discrete resistances or resistor networks. In the current chapter we will examine these various technologies and discuss their relative merits.
The technology of precision wirewound resistors is not fundamentally different from that of power resistors. The only difference lies in the nature (the use of Karma alloys, for example. See Chap. 2) and heat treatment of the resistive wire prior to use designed to improve the TCR of the alloy to about 5 ppm/ C and the care exerted in the construction of the resistor...
