Agilent Technologies 3458A Calibration Manual page 105

Summary
Electronic internal calibration of the 3458A Multimeter simplifies and
shortens the calibration time, while maintaining accuracy and
traceability. This multimeter removes all drift errors, with the
exception of the internal reference standard drift errors. As a result,
the scheme relies on the excellent stability of the reference voltage
and resistor, and superb linearity of the analog to-digital converter.
Depending on the application, auto-calibration using the internal
reference standards results in one or more of the following benefits:
Improved measurement accuracy
•
Extended time between calibrations
•
Extended operating temperature range
•
Reduced errors resulting from other environmentally- caused
•
errors, such as circuit changes with humidity
These benefits are especially significant when compared with earlier
generation multimeters used in metrology, electronic test, and many
other demanding applications.
There are a total of 253 calibration constants stored in the 3458A
Multimeter (these constants can be queried). Of these constants, only
44 are routinely determined from external measurements.
Appendix B Electronic Calibration of the 3458A (Product Note 3458A-3)
Externally Derived Calibration Constants
Offset Constants:
DC volts, 0.1 V to 10 V ranges, Front and rear input terminal
paths; 6 offset constants
Two-wire resistance, 10 W to 1 GW ranges, Front and rear
input terminal paths; 18 offset constants
Four-wire resistance, 10 W to 1 GW ranges, Front and rear
input terminal paths; 18 offset constants
Internal Reference Constants:
Voltage - value of internal reference voltage; 1 constant
Resistance - value of internal reference resistor; 1 constant
Of the remaining 209 calibration constants in the instrument, 6 are
determined through one-time external calibrations. These constants
provide adjustments for frequency and period measurements, time
base interpolation, and the high frequency (beyond 2 MHz) AC
response.
Six additional constants are provided for user convenience. These
constants record the temperature of the last offset calibration, last
external voltage standard calibration, last external resistance standard
calibration, last auto-calibration of DC, last auto-calibration of AC,
and last auto-calibration of resistance.
The remaining 197 constants are determined through internal ratio
transfer measurements as previously described. These constants are
also updated each time auto-calibration
(ACAL ALL) is executed, reducing time, temperature, or
environmentally-induced drift errors. This capability enhances
measurement accuracies over extended time intervals and operating
temperature ranges.
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