[volt-nuts] 3458A calibration

[Poul-Henning Kamp]

In message <133426.31358.qm at web57702.mail.re3.yahoo.com>, Randy Scott writes:

>Can someone explain this to me?  The 3458A's A/D converter uses
>+/-12V reference voltages, presumably derived from the internal
>7.2V reference.

The A/D is so precise that they can use it to calculate ratios
quite precisely.

They measure the external 10V and then the internal 7V and since
the 12V reference does not drift much over a minute, the value
of the 7V in absolute terms is now known.

Later, when you run ACAL, the 7V is measured, and using the
recorded absolute value, the voltage of the 12V reference is
calculated.

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