Even in this digital age, a number of measurement and instrumentation applications rely on the accuracy of the value of one or more resistors.

To guarantee the performance of the system, the designer must understand what factors can affect the value of precision resistor, and how the combined effect of these factors may be evaluated.

There are essentially three types of error source to be understood. The first is measurement errors, which limit the precision with which the actual resistance value can be known. Secondly, short-term change factors, reflecting uncertainty in the resistance value in a customer’s recently assembled PCB. Thirdly, long-term change factors, reflecting value drift throughout the product’s life. The combination of all these factors is termed total excursion.

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