B Electronic Calibration of the 3458A (Product Note 3458A-3)
126 Keysight 3458A Calibration Manual
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.
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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