Chapter 2
Using Your NI 4472
©
National Instruments Corporation
2-11
NI 4472 User Manual
Selecting Your Sample Clock Frequency
The eight analog input channels of the NI 4472 are simultaneously sampled
at any software-programmable rate from 102.4 kS/s down to 1.0 kS/s in
190.7 µS/s increments for
f
s
> 51.2 kS/s or 95.37 µS/s increments for
f
s
≤
51.2 kS/s. The device uses direct digital synthesis (DDS) technology so
that you can choose the correct sample rate for your application. All the
input channels acquire data at the same rate. One input channel
cannot
acquire data at a different rate from another input channel.
Note
If you do not specify a rate at a multiple of the increment, NI-DAQ will
automatically choose the next higher step for you.
Note
Unlike other converter technologies, delta-sigma converters must be run
continuously and at a minimum clock rate to operate within specifications. Although the
software will let you use a lower sample rate, you must
always
use a sample rate of at least
1.0 kS/s to ensure the accuracy of your data acquisition.
Synchronizing Multiple Devices
The NI 4472 can send or receive the DDS clock signal and the
synchronization start signal to or from other NI 4472 devices on the same
bus to synchronize data acquisition. In a multi-device system, a master
device drives the clock and synchronization signals to other slave, or
receiving, devices.
Caution
Do
not
use RTSI 5/TRIG 5 to drive any signals in your system if you are
synchronizing multiple NI 4472 for PXI/CompactPCI devices. The synchronization signal
is driven on RTSI 5/TRIG 5, so driving other signals on RTSI 5/TRIG 5 could lead to
double-driving the line, which can result in unpredictable behavior and might damage your
system.
♦
NI 4472 for PCI
In a PCI system, any NI 4472 can be the master. The master broadcasts the
ADC oversample clock to the other NI 4472 devices and synchronizes the
start of the acquisition using reserved lines in the RTSI cable.
For specific LabVIEW programming instructions, refer to
Synchronizing
Multiple PCI-DSA Devices
in
LabVIEW Help
(
Start»Programs»National
Instruments»LabVIEW 6»LabVIEW Help
). For using NI-DAQ with