Fluke aug96pp2 free download

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MAINTAINING 10 VDC AT 0.3 PPM OR BETTER IN YOUR LABORATORY Ray Kletke Fluke Corporation Everett, Washington Abstract There is a need today to maintain dc voltage at an uncertainty of 0.3 ppm or better. We believe that most standards laboratories can do this without using an expensive Josephson Junction Array System. DC Reference Standards commonly in use today are capable of this performance providing that they are properly calibrated and that the effects of temperature, pressure and seasons are taken into account. This paper develops supporting uncertainty equations and applies them to useful scenarios. Introduction High end multifunction calibrators and digital voltmeters today require calibration uncertainties that only primary standards laboratories maintained in recent history. Uncertainties of 1.0 to 1.5 ppm are required for 10 VDC at the time of test. These standards, in turn, must be supported by reference standards having a NIST traceable uncertainty of 0.3 to 0.5 ppm if a reasonable Test Uncertainty Ratio (TUR) is to be maintained. It is possible today to maintain 10 VDC at 0.3 ppm or better in most standards laboratories without a Josephson Junction Array. However, care must be taken to minimize the effects of certain stimuli that usually contributes negligible error and, therefore, is overlooked. This paper examines some of those effects and recommends how they can be controlled so as to achieve 0.3 ppm performance or better. Classical Approach The classical approach for estimating the uncertainty of the dc voltage standard is simply to combine its stability, as specified by the manufacturer, with the uncertainty of the calibration as follows: = stab + U 2 2 U tot cal Modern zener type dc voltage standards typically have a stability of 2 ppm per year. Assuming this value and a calibration uncertainty of 0.1 ppm, the total uncertainty can be calculated as a function of time. Figure 1 gives the total uncertainty for a single cell and triple cell dc voltage standard (DCVS) as a function of its calibration cycle in months. It shows that the 0.3 ppm goal can be approached for the singe cell DCVS only if it is calibrated with a Josephson Junction Array System every two months or less. This may 1 .2 0 1 .0 0 0 .8 0 ppm 0 .6 0 0 .4 0 3 C e ll G r o u p 0 .2 0 S in gle C e ll 0 .0 0 2 2 .5 3 3 .5 4 4 .5 5 5 .5 6 C alib r a