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The device can be daisy-chained to each other or connected to external networks that support
802.1AS synchronization, and all device timebases will be automatically synchronized. Refer
to
Synchronization across a Network
for more information about supported topologies and
other technical requirements.
Network-synchronized devices can also take advantage of time-based synchronization features
in NI-DAQmx. Certain triggers can be specified in terms of time of day. Time-based triggers
and multidevice tasks (spanning multiple network-synchronized FieldDAQ devices) can help
simplify programming for large systems.
Time triggers can be specified in Host Time or I/O Device Time, depending on the needs of
your application.
•
I/O Device Time
—The time the FieldDAQ device uses internally. This time is
determined by the network configuration and is shared by all 802.1AS
network-synchronized devices on your subnet.
•
Host Time
—The time on your computer or NI Linux Real-Time controller. This is
usually the current global time, and is provided by a local real-time clock or a network
time protocol (NTP) server.
NI-DAQmx automatically translates from Host Time to I/O Device Time as necessary. The
accuracy of this translation depends on the relationship between these times and can reduce the
relative accuracy of time triggers across multiple devices. For maximum accuracy, use an
NI Linux Real-Time controller as the host in a supported topology. However, NI-DAQmx
guarantees that two tasks configured to start at the same host time always start at the same
I/O Device Time in all scenarios, preserving precise synchronization between chassis in this
common use case. Refer to the
Time Triggering
topic in the
NI-DAQmx Help
for more
information on accessing time-based features in the NI-DAQmx API.
Timebases
The following figure shows the FD-11613 clock routing circuitry and timebases.
Figure 13. Clock Routing Circuitry
÷
4
÷
200
80 MHz Timebase
100 kHz Timebase
20 MHz Timebase
Clock
Generator
Onboard
100 MHz
Oscillator
You can use the 80 MHz, 20 MHz, and 100 kHz timebases to generate the measurement
signals. The 80 MHz timebase is generated directly from the onboard clock generator. The
20 MHz and 100 kHz timebases are generated by dividing down the 80 MHz timebase.
Refer to the
FieldDAQ Timing Considerations
and
Master Timebase Synchronization
topics in
the
NI-DAQmx Help
for more information about configuring timing in the NI-DAQmx API.
FD-11613 User Guide
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© National Instruments
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