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SCPI Commands for the Digital Multimeter
VX4101A MultiPaq Instrument User Manual
3–245
NOTE. The formula to calculate aperture from expected resolution is the inverse.
Aperture = .2 * Range^2 / (300000. * Resolution)^2
For the 1.5 A current range and the 300 MW resistance range, use a Range of
1.5 Amps and 54 Gohms respectively, in the formulas above.
Expected resolution is only an approximation. If you are concerned about
optimizing the tradeoff between aperture/ test time and accuracy, use the
Accuracy Specifications in the Appendix to determine an aperture. The
accuracies and apertures listed in the Appendix are tested at the factory. The
accuracy at apertures in between those tested may be assumed to change
logarithmically from one specified aperture to the next aperture. For example , if
the accuracy for some measurement level calculates to 120 mV for a .2 second
aperture, and 140 mV for a .0167 second aperture, the accuracy for a .05 second
aperture may be calculated as follows:
140 mV = 120 mV + k*log(.2/.0167), solving for k, k= 18.547 mV.
.05 second aperture accuracy = 120 mV + 18.547 mV * log(.2/.05) =
131.2 mV.
NOTE. Before choosing an aperture that is not a power line cycle integer
multiple, it should be noted that the accuracy specifications assume a quiet
power environment. In many testing environments, the power line noise
contributes measurable error, particularly in the most sensitive voltage ranges
and in the highest resistance ranges. An aperture that is a power line cycle
integer multiple is recommended.
Finally, if autoranging is enabled, the aperture value will remain unchanged if
the DMM input range changes. However, the expected resolution value will be
recalculated based on the new range found.
Example. If the command SENSe:VOLT:DC:RESolution 2.8e-4 were given, and
the current DC voltage range were 30; the aperture of the measurement would
be:
Aperture= .2 × 30. × 30./300000 × 2.8c-4)
2
= 0.025510 seconds
To determine the rounded aperture, divide 0.25510 by the aperture step size of
.0008333 and round the result of 30.61 to 30.
The resulting aperture is: 30 × .0008333
The SENSe[.....]? query return the requested information.