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EX1629 Multi-Instrument Operation
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NTRODUCTION
While a single EX1629 provides a sophisticated strain gage instrument, the ability to connect
multiple instruments together as an ensemble, creating a single, high sample-rate, high channel-
count acquisition system provides enormous power. This section describes how configure such
systems. Please refer to
Synchronizing Multiple Instruments
for a detailed example with software.
In a multi-instrument configuration, one device is selected as a master and one or more devices are
slaves. The master device sources (outputs) its sample clock and synchronization signal. These
signals allow the master and slave(s) to synchronize their ADCs so that sampled data is phase-
aligned and coherently acquired. In addition, depending on the triggering needs, the master device
may output an arm and/or a trigger signal. This section describes some common multi-instrument
configurations.
Distributing Sample Clock and Synchronization Signals
To guarantee that all instruments in a multi-instrument configuration acquire coherent, phase-
aligned data, a single instrument (the “master”) is chosen by the application designer to share its
internal sample clock and synchronization signals with one or more slave instruments. These
signals are distributed to the slaves via the LXI Trigger Bus.
NOTE
The sample clock and synchronization signals may only be distributed via the LXI Trigger Bus.
Further, only an EX1629 instrument can provide these signals – no external oscillators or
synchronization signals are supported.
Due to hardware constraints, only certain LXI Trigger Bus lines may be used to distribute the
sample clock and synchronization signals (see vtex1629_set_sample_clock_source and
vtex1629_set_synch_source for more detailed information). Each instrument has two LXI Trigger
Bus Connectors that are connected together internally – they are functionally identical. When the
LXI Trigger Bus is used, both connectors must be attached to either an LXI Trigger Bus Cable or
a Trigger Bus Terminator. All LXI Trigger Bus configurations must involve two LXI Trigger Bus
Terminators, one at each end of the bus.
NOTE
When the LXI Trigger Bus is not being used (e.g., standalone mode) no LXI Trigger Bus
Terminators are needed.
Generally, there are two topologies for distributing these signals: Daisy-Chain and Star. In the
daisy-chain topology, devices are connected serially, with two LXI Trigger Bus Cables connected
to each instrument, except the two instruments at the ends of the daisy-chain, both of which have
only a single LXI Trigger Bus Cable connected, with an LXI Trigger Bus Terminator on the other
connector. The Daisy-Chain configuration is suitable for smaller ensembles of instruments, two to
twenty.
Содержание EX1629
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