This is regarding clarificat​ion regarding frequency responce analysis

Question

This is regarding clarification regarding frequency responce analysis
using
NI
PCI 4551 add-on card, especially in the singal generation part for
stimulating
the unit under test.
1. Is it possible to generate sine, step, ramp and arbitrary waveforms
using
this particular card?
2. Ifso what is the range of frequencies that can be possible to
generate
using
PCI 4551 card?( we may require from 1mHz to 2kHZ)
3. And what is the maximum amplitude of the generated signal for full
scale
value?
4. Whether real-time octave analysis for NI DSA software can serve the
purpose
of following tests: Frequency response test, Step response test,
Velocity
test,
Strain Measurement, Linearity Test, Cyclic test.
Or any other software tool is required?
Regards,
Sreedhar T

Answer 1

Hi SreedharT,
In response to your questions, I've included my responses. I highly advise referencing the NI-4551 User Manual for more details.
1. Is it possible to generate sine, step, ramp and arbitrary waveforms
using this particular card?
NI-DSA includes functions to generate standard white noise, pink noise, band-limited noise, periodic white noise, single or dual-tone sine, and chirp signals. For step, ramp, and any other arbitrary waveforms you can use NI-DSA to define and generate an arbitrary analog output signal.
There is a good example which ships with NI-DSA that demonstrates how to generate arbitrary waveforms on the NI-4551. You can find this example in the NI-DSA function palette in LabVIEW under Application Examples>>Advanced>>Arbitrary Output Example.
By default, this example outputs a swept sine wave, but you can change the waveform to whatever you need.
2. If so, what is the range of frequencies that can be possible to
generate using PCI 4551 card?( we may require from 1mHz to 2kHZ)
The maximum output frequency you can generate with NI-DSA is 23 kHz. This limit is governed by the maximum output sampling rate of 51.2 kS/s. Because the digital-to-analog converters on the NI 455x DSA devices feature sharp roll-off, anti-imaging filters, you can generate a spectrally pure sine tone up to 23 kHz with minimal quantization noise, so when using the NI 455x devices, you do not need to worry about the output signal becoming choppy or noisy when approaching the Nyquist frequency.
The minimum frequency you can set is 0.1 Hz. This is limited by the finite size of the output buffer and the minimum update rate for the DAC. The output buffer is limited to 4,096 samples, and the DAC must maintain a minimum rate of 1.25kS/s for accurate results.
In Octave Analyzer Mode, when you're inputting a certain frequency, keep in mind the input range differs for each analysis type and the two configurable center frequencies. I've included the frequency ranges for a single channel below.
1/1-octave analysis
center frequency fs=25.6 kHz:
High: 8 kHz
Low: 16 Hz
fs=51.2 kHz
High: 16 kHz
Low: 31.5 Hz
1/3-octave analysis
fs=25.6 kHz
High: 10 kHz
Low 12.5 Hz
fs=51.2 kHz
High: 20 kHz
Low: 25 Hz
1/12-octave analysis
fs=25.6 kHz
High: 10.68 kHz
Low: 11.05 Hz
fs=51.2 kHz
High: 5.34 kHz
Low: 5.52 Hz
3. And what is the maximum amplitude of the generated signal for full
scale value?
The maximum amplitude is equal to the voltage range for the selected output channel.
4. Whether real-time octave analysis for NI DSA software can serve the
purpose of following tests: Frequency response test, Step response test,
Velocity test, Strain Measurement, Linearity Test, Cyclic test.
Or any other software tool is required?
The NI-DSA Real-Time Octave Analysis software add-on for NI-DSA supports fractional-octave analysis for 1/1, 1/3, and 1/12 octave analysis, level measurements, and A-, B-, and C-weighting. You can do octave, level, or both octave and level measurements, and have the additional option of specifying the weighting if required. This is all that can be done in real-time.
To perform a frequency response test, it is preferable to use the swept-sine analysis mode of the NI-4551 rather than a broadband FFT-based frequency response. Swept-sine analysis provides two main advantages over a broadband frequency response measurement in which all frequencies are excited and measured simultaneously. The first is a wider dynamic range. The second is flexible measurements of signal distortion and nonlinearity. For more information of swept-sine analysis, please refer to the NI-DSA Software Manual downloadable off our web site. http://www.ni.com/
For the Velocity test, Strain Measurement, Linearity Test, and Cyclic Test I should ask for more information about each test before attempting an answer. However, to answer your question, there are no methods I know of in NI-DSA that would directly perform these tests. In contrast with that answer, you may be surprised this functionality may be included with a LabVIEW development environment.
Let me know if you have further questions or this does not resolve your issue!
Chad AE
Applications Engineer