VoltRef  Voltage Scaling System 

The following simplified method compares the different outputs of voltage standards. It enables users to make comparisons between different outputs up to 50 volts. Comparisons can be made between 1, 1.018 and 10 volts to better than 0.5 ppm. This system is included in the VRMP software described in the previous section. The only equipment needed besides the software is a Low Thermal Scanner and a voltmeter with sufficient resolution and linearity. 
then taken as before. These readings are adjusted using the preliminary meter correction. Computed values are found for the 10volt units from the leastsquaresfit calculation that are biased on the known 1volt values. The final meter correction is found by adjusting the correction so that the adjusted computed values for the 10volt devices are equal to their adjusted measured values. By using the method described only the meter readings at 9 and 10 volts are significant in determining the final values for the 10volt units.  
TENTOONE
PROCEDURE A calibration ratio for the meter is calculated by dividing the actual readings by the known value of each of the traceable reference units. This calibration factor is then applied to each of the difference measurements. The corrected measurements are used in the leastsquaresfit calculation to determine the unknown values. 

When using 10volt traceable reference units this procedure works very well. Since the readings between pairs will be approximately 9 volts, and the calibration is done at 10 volts, the voltmeter need have good linearity only over the range of 9 to 10 volts. The values for the 1volt units are computed from the leastsquaresfit calculation. ONETOTEN PROCEDURE In this procedure the measured value for each 10volt device in the test is taken along with the traceable 1 or 1.018volt reference devices. A preliminary meter correction is found. The difference measurements are 
RESULTS The accuracy of the scaling procedure is primarily dependent on the meter linearity and on the resolution available on the 10volt range. Tests using the procedure with two commercially available voltmeters have been done at laboratories that have 10volt Josephson arrays. Many test runs show that values obtained with the scaling procedure lie within 0.5 ppm of measurements made directly against the Josephson arrays. Typical measurement differences were about 0.2 ppm. The two meters tested were the HewlettPackard 3458A and the Datron 1281. Several of each of these two models were used.. Laboratories can now take advantage of the superior longterm stability of saturated cells to maintain their volt, while using the more rugged solidstate devices as working standards and for volt transfers between laboratories.



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