Section 2: General operation
Model 2657A High Power System SourceMeter® Instrument Reference Manual
2-22
2657A-901-01 Rev. B/December 2012
Figure 6: Fundamental source-measure configurations
Operation considerations for the ADC
The following paragraphs discuss autozero and NPLC caching. Autozero and NPLC caching only
apply to the integrating
(on page 4-1) (ADC). They are not used with the
fast (high-speed) ADC.
Autozero
The integrating ADC of the Model 2657A uses a ratiometric A/D conversion technique. To ensure
accuracy of readings, the instrument must periodically obtain fresh measurements of its internal
ground and voltage reference. Separate reference and zero measurements are used for each
aperture.
As summarized in the "Autozero settings" table, there are three different settings for autozero. By
default, the instrument automatically checks these reference measurements whenever a signal
measurement is made (AUTO). If the reference measurements are out of date when a signal
measurement is made, the instrument will automatically take two more A/D conversions, one for the
reference and one for the zero, before returning the result. Thus, occasionally, a measurement takes
longer than normal.
B: Source I
A: Source V
V-meter
I-source
I-meter
A
I-meter
A
V
V-meter
V
V-source
+
-
Summary of Contents for 2657A
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