24-Bit, 204.8 kS/s Dynamic Signal Acquisition and Generation
With 118 dB dynamic range and low noise and distortion, NI 446x
devices can make very accurate frequency-domain measurements. They
have excellent amplitude flatness of 0.1 dB within the frequency range
of DC to 92 kHz, and have a typical THD of -107 dB.
TTL/CMOS-compatible and is activated by a choice of rising or falling edge.
Triggering is needed in applications that acquire transient signals. When
performing structural analysis by striking a metal beam with a hammer, for
instance, you measure transient vibrations with accelerometers with
acquisition triggered by the hammer impact.
Antialiasing
The analog inputs have both analog and digital filters implemented in
hardware to prevent aliasing. Input signals are first passed through a fixed
analog filter to remove any signals with frequency components beyond the
range of the ADCs. Then digital antialiasing filters automatically adjust
their cutoff frequency to remove any frequency components above half the
programmed sampling rate.
Calibration
National Instruments calibrates the offset voltage and gain accuracy of the
analog inputs and outputs. An onboard precision voltage reference ensures
that the gain and offset remain stable and accurate. NIST-traceable and
ISO 9002-certified calibration certificates are available on request.
Analog Outputs
NI 4461 devices have two channels of 24-bit resolution, high-fidelity
analog output. A common application of the analog output is to stimulate
a system under test while measuring the frequency response with the
analog inputs. The output conversions occur simultaneously at software-
programmable rates up to 204.8 kS/s. The analog output circuitry uses
8-times oversampling interpolators with 64-times oversampling delta-sigma
modulators to offer exceptional spectral purity. Software-programmable
Figure 2. With application software such as NI LabVIEW, you can conduct
frequency-response, swept-sine, and other common audio measurements.
attenuation of 0, 20, or 40 dB is available on the output channels. NI 4461 Software
devices have excellent amplitude flatness of 0.1 dB within DC to 92 kHz,
NI Measurement Services Software
and a THD of -95 dB at 1 kHz. You can simultaneously acquire data on the
input channels while updating the output channels.
NI 446x devices use NI measurement services software, based on the
NI-DAQmx driver, as the hardware and OS interface. You can build
automated test systems or integrate an NI 446x with other hardware,
including modular instruments and multifunction data acquisition (DAQ)
products, through NI-DAQmx function calls. NI measurement services
software also includes DAQ Assistant, an interactive guide that steps
you through configuring, testing, and programming measurement tasks
and generates the necessary code automatically for National
Anti-Imaging
NI 4461 output channels have both analog and digital anti-imaging
filters. These filters remove the unwanted out-of-band components
generated when an analog signal is produced from digital data.
The digital filters limit the bandwidth of the output signal to half the
original conversion rate, thereby rejecting images caused by the 8-times
oversampling process. The signals generated by the analog output
circuitry are low-distortion, low-noise, flat-frequency analog signals.
Instruments LabVIEW, LabWindows/CVI, or Measurement Studio.
Analysis Software
Multimodule Synchronization
LabVIEW Sound and Vibration Toolkit
For applications requiring more channels, you can synchronize the operation NI 446x devices are well-suited for audio, acoustic, and vibration
of two or more NI 446x devices with less than 0.1 deg phase mismatch.
Synchronization is achieved by sharing a digital trigger and clock between
analysis applications. The LabVIEW Sound and Vibration Toolkit
incorporates Express technology to make it easier for you to perform
multiple modules. The NI-DAQmx driver software automatically handles the sound and vibration measurement and analysis. The toolkit includes
synchronization of multiple devices in a single task.
LabVIEW Express VIs for:
• Fractional-octave analysis with weighting
• Integrated vibration level
• Weighted sound level
• Zoom power spectrum
• Peak search
Triggering
NI 446x devices offer both analog and digital triggering for signal
acquisition. The source of the trigger can come from any analog input
channel, the external digital trigger input, the PXI trigger bus (PXI devices),
or the RTSI bus (PCI devices). The external digital trigger is 5 V
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