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Chapter 3
Acquiring Analog Input
acquisition continues until you stop the operation. Continuous acquisition is also
referred to as double-buffered or circular-buffered acquisition.
If data cannot be transferred across the bus fast enough, the FIFO becomes full. New
acquisitions overwrite data in the FIFO before it can be transferred to host memory.
The device generates an error in this case. With continuous operations, if the
application program does not read data out of the PC buffer fast enough to keep up
with the data transfer, the buffer could reach an overflow condition, causing an error
to be generated.
•
Hardware-timed single point (HWTSP)—Typically, HWTSP operations are used to read
single samples at known time intervals. While buffered operations are optimized for high
throughput, HWTSP operations are optimized for low latency and low jitter. In addition,
HWTSP can notify software if it falls behind hardware. These features make HWTSP ideal
for real-time control applications. HWTSP operations, in conjunction with the
wait for
next sample clock
function, provide tight synchronization between the software layer
and the hardware layer. Refer to the white paper
NI-DAQmx Hardware-Timed Single Point
Lateness Checking
for more information. To access this document, go to
and enter the Info Code
daqhwtsp
.
Aggregate versus Single Channel Sampling Rates
The PXIe-4310 module has one ADC per channel, so the single channel maximum sample rate
can be achieved on all channels simultaneously.
The total aggregate sample rate determines the maximum bus bandwidth used by the device. The
aggregate sample rate is the product of the maximum sample rate for a single channel multiplied
by the number of AI channels that the device supports.
Table 3-1 shows the single channel and total aggregate rates for PXIe-4310 module.
Getting Started with AI Applications in Software
You can use a PXIe-4310 module in the following simultaneous analog input applications:
•
Single-point analog input
•
Finite analog input
•
Continuous analog input
The PXIe-4310 module uses the NI-DAQmx driver. NI-DAQmx includes a collection of
programming examples to help you get started developing an application. You can modify
examples to develop a new application or add example code to an existing application.
Table 3-1.
Analog Input Rates for PXIe-4310 Module
Single Channel
Total Aggregate
400 kS/s
3.2 MS/s
