Capell, Frank (1991, ASQC) John Fluke Mfg. Co., Inc., Everett, WA
This is the third paper in a series. It describes the circuit diagram, the self-adjustment routines of the microprocessor-controlled multimeter calibrator, and the ability of the calibrator to check changes in its own calibration from time to time after its initial self-adjustment.
The output values the calibrator assigns to itself when it is initially adjusted are compared with its output values, then immediately measured by external standards. A record of its internally-measured changes in calibration is statistically correlated with measurements made by external standards. Self-adjustment of the calibrator is accomplished in four basic steps: (1) Self-test Pulse Width Modulated Digital-to-Analog-Converter (PWMDAC) linearity; (2) Transfer values from external standards to internal references; (3) Disseminate values of internal references to all ranges and functions; and (4) Store calibration data obtained during self-adjustment in non-volatile memory.
A large amount of data is automatically collected by the calibrator's microprocessor. The collection of additional data from repeated external verification can also be automated. When the collected data is compared, the calibrator's performances can be characterized; then external verification intervals can be minimized. A characterized calibrator can have an improved test uncertainty ratio (TUR) and/or an extended calibration interval.
John Fluke Mfg. Co., Inc.,Metrology,Statistical tests,Calibration