National-instruments Data Acquisition Device NI USB-621x Instrukcja Użytkownika Pobierz pdf (Strona 44)

Chapter 4 Analog Input

Analog Input Timing Signals

In order to provide all of the timing functionality described throughout this

section, USB-621x devices have a flexible timing engine. Figure 4-4

summarizes all of the timing options provided by the analog input timing

engine.

Figure 4-4. Analog Input Timing Options

USB-621x devices use AI Sample Clock (ai/SampleClock) and AI Convert

Clock (ai/ConvertClock) to perform interval sampling. As Figure 4-5

shows, AI Sample Clock controls the sample period, which is determined

by the following equation:

1/Sample Period = Sample Rate

20 MHz Timebase

100 kHz Timebase

Programmable

Clock

Divider

Programmable

Clock

Divider

AI Sample

Clock

Timebase

AI Convert

Clock

Timebase

Analog Comparison Event

Ctr n Internal Output

SW Pulse

Ctr n Internal Output

AI Convert Cloc

AI Sample Clock

1 2 ... 39 40 41 42 43 44 45 46 47 48 49 ... 184 185

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