Ai Convert Clock Signal; Using An Internal Source; Using An External Source; Routing Ai Convert Clock To An Output Terminal - National Instruments Data Acquisition Device NI USB-621x User Manual

Chapter 4 Analog Input

AI Convert Clock Signal

Setting the conversion rate higher than the maximum rate specified for your
Caution
device will result in errors.
NI USB-621x User Manual
Use the AI Convert Clock (ai/ConvertClock) signal to initiate a single A/D
conversion on a single channel. A sample (controlled by the AI Sample
Clock) consists of one or more conversions.
You can specify either an internal or external signal as the source of
AI Convert Clock. You also can specify whether the measurement sample
begins on the rising edge or falling edge of AI Convert Clock.
By default, NI-DAQmx chooses the fastest conversion rate possible based
on the speed of the A/D converter and adds 10 μs of padding between each
channel to allow for adequate settling time. This scheme enables the
channels to approximate simultaneous sampling and still allow for
adequate settling time. If the AI Sample Clock rate is too fast to allow
for this 10 μs of padding, NI-DAQmx chooses the conversion rate so that
the AI Convert Clock pulses are evenly spaced throughout the sample.
To explicitly specify the conversion rate, use AI Convert Clock Rate
DAQmx Timing property node or function.

Using an Internal Source

One of the following internal signals can drive AI Convert Clock:
• AI Convert Clock Timebase (divided down)
• Counter n Internal Output
A programmable internal counter divides down the AI Convert Clock
Timebase to generate AI Convert Clock. Started by AI Sample Clock, the
counter counts down to zero, produces an AI Convert Clock, reloads itself,
and repeats the process until the sample is finished. It then reloads itself in
preparation for the next AI Sample Clock pulse.

Using an External Source

Use any input PFI line as the source of AI Convert Clock.

Routing AI Convert Clock to an Output Terminal

You can route AI Convert Clock (as an active low signal) out to any output
PFI terminal.
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