National Instruments NI 6601, Руководство пользователя

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Chapter 2 Device Overview
© National Instruments Corporation 2-9 NI 660x User Manual
Note Transfer rates may vary depending on yo u r comp u ter hardware, operating system
and system activity. This benchmark data was determined on an AMD Athlon XP 1800
comp
u ter with 128 MB of PC-2100 DDR RAM r u nning Windows XP and LabVIEW u sing
one co u nter of the TIO device. For contin u o u s meas u rements, the transfer rate is the
maxim u m s u stained rate for 30 seconds on one co u nter.
High Precision Clock (NI 6608)
The acc u racy of yo u r time meas u rement and p u lse generation is determined
by the timing acc u racy of yo u r co u nter clock. The NI 6608 device has an
oven-controlled crystal oscillator (OCXO) that provides a highly stable
10 MHz clock that yo
u can u se as a GATE or SOURCE of a co u nter. Yo u
can also u se the OCXO as the PXI backplane clock. Mod u les phase locked
to the PXI backplane clock will acq u ire the same clock stability as the
NI 6608. For more information, refer to the KnowledgeBase at
ni.com/
s upport
and search u sing keyword
pha s e lock
.
Using the OCXO as the SOURCE Counter
Using the OCXO as the timebase so u rce of the co u nter, yo u can ro u te the
10 MHz clock to Ctr n So u rce.
Using the OCXO as the 10 MHz PXI Backplane Clock
Yo u r PXI chassis has a b u ilt-in 10 MHz backplane clock that is
independently ro u ted to each peripheral slot. An independent b u ffer on the
chassis drives the clock signal to each peripheral slot with a skew of less
than 1 ns between slots. Yo
u can u se this common reference clock signal to
synchronize m u ltiple mod u les in a meas u rement or control system.
Use the OCXO 10 MHz clock to drive the PXI backplane clock so the
mod
u les in the other slots can take advantage of the stable timebase.
Note On NI PXI-660 x devices, the maxim u m timebase is phase locked to the PXI
backplane clock.
To u se the OCXO 10 MHz clock as the PXI backplane clock, pl u g the
NI PXI-6608 device into Slot 2, or the slot immediately to the right of the
controller of the PXI chassis.
By defa u lt, NI-DAQ software drives the 10 MHz clock from the OCXO
onto the PXI CLK10 in pin so that the OCXO is u sed as the PXI backplane
clock. When the PXI chassis senses a clock on the PXI CLK10 in pin in