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Introduction and Specifications
Calibration Check
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1-11
• Except for the internal ac/dc transfer standard, the internal check standards are
directly calibrated by traceable external standards every time the 5700A/5720A
Series II is calibrated.
• The internal ac/dc transfer standard is never adjusted, so its traceability is not
disturbed by calibration. Infrequent verification is done in the traditional way, by
comparing selected ac voltage outputs with an external dc voltage standard through
an external ac/dc transfer standard. Fluke recommends this be done every two years,
or as determined by the policy of your organization.
• Infrequent independent verification is also performed on stable parameters, such as
frequency flatness, determined more by circuit geometry and dielectric constants
than time.
1-19. Calibration Reports
The calibrator stores two sets of calibration constants: the set currently in use and the old
set from the previous calibration. This gives the calibrator the ability at any time to
produce a calibration report of the differences between the present settings and the
settings that were in effect before the last calibration. The report shows changes for each
range and function in +/- ppm of range and in percentage of specification limit. You can
print the report or send it to a host computer through either the RS-232-C or IEEE-488
interface.
If you request a calibration report after doing calibration but before saving the new
constants, the report shows proposed changes to the calibration constants relative to the
previously stored settings.
1-20. Calibration Check
Checking the calibration takes about an hour, and provides you with a means of
documenting the calibrator’s performance of a between calibrations. Calibration
checking is similar to calibration, except internal check standards are used as primary
references (no external standards are needed), and changes cannot be stored. The process
produces a report similar to normal calibration, showing drift relative to internal check
standards. Because cal check does not change stored calibration constants, there is no
need to enable the rear panel CALIBRATION switch. Therefore, an external computer
can do the procedure unattended.
1-21. Developing a Performance History
A Fluke specification is a set of performance limits that all products must meet. To
maintain consistent quality, Fluke calibrators are specified with enough margin to
include temperature, line, and load extremes, plus additional margin for production. This
means that a typical 5700A/5720A Series II calibrator in a typical environment operates
inside 50% of specification limits. For some exacting applications, it can be helpful to
know just how accurately a particular calibrator operates. The proper way to do this is to
accumulate a performance history by calibrating regularly and recording results on a
control chart.
Calibrating regularly and recording the results on a control chart is tedious and requires a
large array of equipment. The calibrator’s calibration check feature is an alternative with
some distinct advantages:
• Calibrated check standards are already programmed into the unit. You do not have to
use external standards.