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Artifact calibration theory and application Application Note Introduction Electronic instruments gen- erally contain both a large number and a wide variety of components. The circuit con- figuration and the values of the components determine the characteristics of the instru- ment. Unfortunately, because nothing is absolutely stable, the value of any component varies with time, and because of this, instruments require periodic calibration to assure continued compliance with specifications. Until the advent of the micro- processor, periodic calibration generally required the physi- cal adjustment of components within the instrument. This was done to bring the instrument into compliance with external standards. Complex instruments might contain dozens of internal physical adjustment points such as potentiometers and vari- able capacitors. The adjustment process could take many hours Figure 1. A Calibration Lab in an Instrument. to complete. This approach to calibration requires traceable stimulus and measurement at each of these In the mid-1970s, instru- standards) has been utilized points. The systems used have mentation broke new ground extensively in the calibration been both manually operated by using the microprocessor, of instruments. Today, inter- and complex. Such systems not only to enhance capabili- nal software corrections have may include various refer- ties and operation, but also to eliminated the need to remove ence components or stimulus simplify the calibration process. instrument covers to make values, as well as bridges and For example, the Fluke 8500A physical adjustments in almost other instruments. The support (a high-accuracy multimeter) all types of instrumentation. of these complex and lengthy was designed to store and use However, for instruments that calibrations required a large software correction factors do not support Artifact Calibra- and costly array of equipment, to compensate for gain and tion (defined below), it is still processes and manpower. zero errors on each range of necessary to provide a large the instrument. This process array of external stimulus or of storing constants (based measurement capability for on comparison to external