© National Instruments
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acquisition. Refer to the
section for more details about how this
affects analog trigger events.
•
On demand software sampling returns a single sample from an acquisition running at the
maximum supported sample rate of the module. For any on-demand, software timed
acquisition the PXIe-4340 waits for the group delay to elapse before returning the sample.
As a result, the data returned aligns closely in time with the software request and is delayed
by the sum of the analog input delay and digital filter delay.
1
Synchronizing Channels
Channels on the same board configured with the same excitation frequency and amplitude are
automatically synchronized. You can synchronize more than two channels used for resolvers or
combinations of resolvers, LVDTs, RVDTs, and synchros. You can also synchronize more than
two channels used for resolvers or combinations of resolvers, LVDTs, RVDTs, and synchros by
assigning the same voltage and frequency across the channels.
Hardware-Timed Single Point Acquisitions
Hardware-Timed Single Point (HWTSP) is a Hardware-Timed Acquisition Mode in which a
digital hardware signal (Sample Clock) controls the rate of the acquisition. The Sample Clock
signal can be imported or internally generated on the PXIe-4340 using the sample rate
configured with a NI-DAQmx task.
During Buffered acquisitions, the device may wait to transfer data to the host machine to build
larger bus transactions. This optimizes throughput. During HWTSP acquisitions, the device
sends data to the host in response to every sample clock. This optimizes latency.
These features make HWTSP ideal for real-time control applications. HWTSP acquisitions, in
conjunction with the wait for next sample clock function, provide more deterministic
synchronization between software and the hardware. Refer to the
NI-DAQmx Hardware-Timed
Single Point Lateness Checking
document for more information. To access this document, go to
and enter the Info Code
daqhwtsp
.
Hardware-Timed Single Point Acquisition Model
The HWTSP data path is optimized for low-latency applications and is different than the data
path used in Buffered Mode acquisitions.
When in HWTSP, the demodulation and sampling systems can be modeled as being decoupled,
which allows you to configure the demodulator and sampling systems independently. This
1
The maximum sample rate of the PXIe-4340 is 25.6 kS/s. In addition to the fixed analog input delay, you
must also account for the digital-filter group delay. For 25.6 kS/s with 5 kHz excitation, the digital filter
group delay is
.
The total delay is 3.01825 ms + 0.7 µs = 3.01895 ms. Refer to the
NI PXIe-4340 Device Specifications
for
more information.
.88544 ms
29 S
25.6 kS/s
---------------------------
+
3.01825 ms
=
