2400 Series SourceMeter
®
User’s Manual Specifications A-7
A/D conversion
This is the time it takes to measure the specified A/D converter phase. In general, there are
three A/D phases required to generate a voltage or current reading. These phases are often
referred to as the signal, reference, and reference zero phases. The signal phase measures
the input signal. The reference and reference zero phases are associated with a precision
voltage reference inside the SourceMeter. By measuring all three phases, zero drift for the
reading is reduced. A/D conversion time is programmable with 0.01 power line cycle
resolution.
When Auto-Zero is enabled, all three phases are measured each time the SourceMeter is
triggered. With Auto-Zero disabled, only the signal is measured. Hence, speed is increased
at the expense of long term drift.
Firmware overhead
This is the time associated with A/D communication, reading calibration, and other opera-
tions necessary to perform the SDM cycle. This time is not illustrated in the following tim-
ing diagrams.
Timing diagrams
Case I: Auto-Zero enabled and measuring a single function
Figure A-1
Case I timing diagram
Trigger Latency: 225µsec max
Source Configuration: 50µsec max
A/D Conversion: [NPLC Setting × (1/power line frequency)] + 185
Firmware Overhead: 1.8msec for Source V
2.15msec for Source I
Trigger
Event
Source
On
Source On Time
Source
Off
Trigger
Delay
Trigger
Latency
Source
Configuration
Source
Delay
A/D
Conversion
(current signal
phase)
A/D
Conversion
(ref phase)
A/D
Conversion
(ref zero phase)
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