Fft find frequency

I am new to Labview. I need to plot the data (2 cols, one is time, x array, the other one is signal intensity,y array)provided by my instructor in time domain, which I already did. Then I need to convert the data into frequency domain. What should I do? I tried FFT function for my y array. But how can I find out the frequency informaiton? From the x array, I know it's sampling rate is 2500Hz. T= 40s, N=100,000. the effective maxmium frequency should be 1250Hz, right?
And I also need to isolate the 1000Hz signal... I am totally confused.
Hope you can help me. Thanks in advance.
John
Solved!
Go to Solution.
Attachments:
raw.vi ‏17 KB

Norbert makes some good points- you need to have a play and maybe get a good book on signal processing (not LabVIEW specific).
The 'effective' frequency you talk about is I assume the Nyquist frequency=sample rate/2. If this is what you mean, you don't have to do anything about it- just be aware that the maximum frequency your power spectrum will show is sample rate/2.
You can isolate a specific time domain signal in the manner you mention, FFT->zero spectral bins you're not interested in->inverse FFT, (use FFT not power spectrum for this). A standard FFT will put out a double sided spectrum, which is symmetrical for time series that do not contain complex numbers, so you will need to blank a given bin on both sides of the spectrum- which is maybe what you were talking about RE: effective frequency. Use the whole thing (not just +ve half) to reconstitute the original signal.
The 'blank a bin and inverse FFT' method is not considered a 'good' way of obtaining time series in a reduced band for real signal processing for reasons I won't explain here. You usually just use a filter on the time series, of which LabVIEW provides many.

Similar Messages

Find frequency from input signal

Hi
How can i find frequencies from input signal (*.txt file) that consist of 7000 samples. I know the sampling rate.

This is a question about this thread.
I am working on a program to pull the two frequencies from a touchtone phone signal and figure out what number was pressed. I used the Spectral Measurements VI to perform an FFT on the data. I want it to work in real time, but I can't figure out how to get the max two frequencies out of the 2D array that is coming out of the Spectral Measurments VI. I am experimenting with the ptbypt functions, but can only get the single MAX value. I need to then compare these with a lookup table. Any ideas?
I am attaching the VI.
Thanks,
Eric
Attachments:
DSP FFT Sound Card AutoPower Spectrum.vi ‏133 KB

TABLE/TCODE to find frequency of Transaction used

We are having a situation in project where we need to find by which Tcode/Table we can have the Frequency of the Transaction codes used.For example:Suppose MM03 or some ZCode is used by the client.Then in last couple of months how many times the same transaction have been used?Is there any TCode/table to idfentify such scenario?
Pointers on this will be highly appreciated and will be helpful.

Hi,
Use Transaction code ST03 or ST03N
a®

How can I find Smart Card frequency ?

I have been developing an ATR parser class to parse ATR, calculate Bauds rate and and something like that, I have two question to ask:
- first is that I don't know where can I find frequency value to calculate Bauds Rare?
- second is that are we able to change any card bauds rate?

Sebastien,
The ATR specifies the "FI" and "DI" parameters which are mapped to respectively the supported clock rate conversion factor F (and maximum frequency fs) and the bitrate adjustment factor D, all of which are used to calculate the ETU and bitrate. Refer to ISO/IEC 7816-3 Section 8, specifically Table 7 and 8.
The clock frequency used by the reader must be supported by the card for a given protocol (T=0, T=1, etc).
EDIT:
This ties in with what you said about PPS exchange (a.k.a. protocol negotiation a.k.a. PTS request):
If the ATR indicates that protocol negotiation is allowed, the reader can send a PTS request to the card containing the reader's preferred choice of the FI and DI parameters for a transmission mode; the card's response will indicate whether those parameters can be used for subsequent communication. Alternatively, the reader can use the first protocol given in the ATR and default values for FI and DI.
This is just an overview - there are many more details regarding protocol negotiation; refer to ISO/IEC 7816 Sections 6.2.4, 6.3 and 9.
Note that protocol negotiation (PTS request) may take place at one time only: after the reader has received the ATR but before it sends any other traffic. Protocol negotiation does not follow the usual command-response APDU exchange format. For this reason the reader (or its driver) handles the negotiation transparently.
I hope that clarifies things...
Adriaan

MyRIO FPGA FFT Express VI timing analysis for multiple input mode - trying to perform fft's on a 3-axis accelerometer

Hi Everyone!
Project Background:
I've been working with the myRIO FPGA in an attempt to generate an application capable of sampling a tri-axis accelerometer and performing an fft on each axis. I've successfully developed an application for a single axis, but attempting to duplicate the code to sample the second and third axes in parallel results in an estimated 150% resource utilization for the tiny FPGA's LUT's. Additionally, I'm looking to avoid sequentially processing each accelerometer input using triggers and a single fft block because that reduces my fft update frequency significantly (e.g. I can't calculate another fft for input 1 until I calculate an fft for inputs 2 and 3).
After reading up on the fft vi, I'm thinking that I can use the M-interval input indexes / Continuous output indexes Input/Output Index Pattern mode. My thought is that I can edit the vi to remove any math that "recombines" these three vectors into a single fft, resulting in 3 separate fft's. I'm also hoping that this process requires less time than using the sequential method described above.
The Questions:
1. Has anyone done an fft on three inputs using the myRIO at sampling rates > 20kHz and fft sizes of 1024 or larger? If so, I may just be lacking some proper resource management.
2. Does anyone know where to find timing information on the M-interval input indexes / Continuous output indexes Input/Output Index Pattern mode? The manual only provides timing diagrams for singel channel / single input modes. I don't want to waste my time modifying the vi if it will still take 3x as long (assuming modifying the vi is even a possibility).
Further Information:
I already have an application written that samples the accelerometers at >20kHz and then performs the fft on the main processor, but now I'm looking to see if it is possible to perform all signal processing on the FPGA side. The processor performs decently enough, but the timing is not as consistent as I would like it to be. Lastly, I am aware that the myRIO itself has a built in accelerometer, but I need to mount the accelerometer in an environment where the myRIO would probably be damaged and definitely cannot fit.
Any thoughts are much appreciated! The excessive FPGA compile times for this thing make the old guess and check method less appealing.
-Chris

Hi Chris,
Thanks for posting and the detailed background on the project! To answer some of your questions:
1. The FFT Express VI does use a significant amount of space. The FPGA on the myRIO is somewhat limited space-wise. Your best option may to implement the FFT for 1 channel on the FPGA and the other two on the RT side.
2. I converted the FFT Express VI to a subVI and I am not sure if you can trim too much code from it. The subVI is also very complex so re-working it would be a significant amount of work. I could not find much documentation on M-interval input indexes / Continuous output indexes Input/Output Index Pattern mode timing.
I hope that this helps!
Thanks,
Frank
Application Engineer
National Instruments

Transient analysis frequency estimate

Hi,
I have a simple analog tone generator that produces a sine wave after some short startup delay. Is there a function in Multisim that would allow me to take my transient analysis data and estimate the frequency of oscillation? What I'm looking for is similar to the frequency counter available in the runtime tools.
Specifically, I need to generate a table of results from a Monte carlo transient analysis. Currently, I'm forced to export the 200 or so MC time series and perform an FFT in MATLAB on each series.
I'm not looking for a monte carlo Fourier analysis, because I need much better resolution than this tool provides. Is there something I can do with the post processor to extract a frequency estimate?
-J

Hi Jay,
In Multisim, you can use the probe or frequency counter to read signal frequency, but once you use any of the analysis such as transient, the option to find frequency is not available.
What you can do is use LabVIEW to control Multisim and there is a pre-built function available that can calculate a signal frequency. To make this work, you need LabVIEW and the LabVIEW Multisim API Toolkit which can be downloaded from the links below:
https://lumen.ni.com/nicif/us/evalmultisimtlkt/content.xhtml
https://lumen.ni.com/nicif/us/evaltlktembdes/content.xhtml
Once you install the required software, in LabVIEW you can create a VI (a program) to launch Multisim, run a circuit 200 times and each time change component values and calculate the output frequency for each run.
Attached is a sample circuit and the VI I created. Double click on the Reading Signal Frequency.vi file, click on the folder in the front panel (the screen with the grey background) and select and select the Multisim circuit which is attached. In this program, I am changing a resistor R1 in the Multisim circuit and run the simulation 10 times, once finished, the result will appear in the array in the front panel.
You can use this example and modify the VI for your circuit.
Tien P.
National Instruments
Attachments:
PhaseShiftOscillator_a.ms12 ‏98 KB
Reading signal Frequency.vi ‏69 KB

How to measure frequency with PCI-4474 card

Hi,
I'm trying to measure frequency with PCI-4474 card.
Any sample code available?
Thanks.

Hi,
Thank you for posting the the NI forums. There aren’t any example programs that ship with the DSA drivers. Will you be using this with the Sound and Vibration Toolkit? If so, there are numerous examples that install with this software package. Check out the LabVIEW Example Finder >> Toolkits and Modules >> Sound and Vibration Toolkit.
In addition to this, you could also use the signal processing VIs that ship with LabVIEW. There are also examples that ship with LabVIEW that use these VI in Example Finder >> Analyzing and Processing Signals FFT and Frequency Analysis. There is an entire Signal Processing palette that should contain the functionality that you need.
I hope this helps. Post back if you have further questions.
Ed W.
Applications Engineer
National Instruments

This is regarding clarification regarding frequency responce analysis

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

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

Realtime fft

Hi
is it possible to do a "realtime"-fft on LV6? I mean, to do a data acquisition (not a sinus-function, just normal sensor data) and see the fft-spectrum and the frequencies and the different modes.
is there an example somewhere.
thanks for your help.
yves

There's lot of examples. Just go to Help>Find Examples>Analyzing and Processing Signals>FFT and Frequency Analysis. There's one called Simple Spectrum Analyzer.vi that's written for use with a daq board. I won't get into a discussion of "realtime" but it does do a continuous power spectrum.

Counter 1 - Measure Frequency & Counter 0 - Generate PWM POSSIBLE?

Is this POSSIBLE with a NI-6025E DAQ card? Can I use the two counters to generate % control a TTL PWM signal and at the same time measure frequency from a circuit? This is my connection.
GPCTR1_SOURCE - connected to find frequency circuit
GPCTR1_OUT - connected to GPCTR0_GATE
GPCTR1-GATE - not in use
GPCTR0_SOURCE - not in use
GPCTR0_OUT - connected to DC motor circuit
GPCTR0-GATE - connected to GPCTR1_OUT
My concern is that changing or controlling the TTL PWM might change the frequency reading. This is because COUNTER O is connected to COUNTER 1.

I understand to measure frequency of a signal there are TWO methods. A ONE counter method and a TWO counter method. I need to measure a frequency between 1 Hz to 200 Hz. Is the ONE counter method possible? What is the ONE counter method?

Display FFT of input signal which receive from VISA read ?

Hi.
I receive data from MCU whcih sampling frequency is constant and we assumed it is S. now I get data from MCU with using VISA read block. I can display data, perform some functios like filtering, multiply and save them in txt files. all thing is OK.
but when I want to see FFT of incomig data on chart , it doesn't work !! I use this VI for calculate and display FFT of input signal (from VISA read) and display it which in Y-Axis is magnitude and X-Axis is frequency.
in your mind why this is not work and what I must done for show input signal FFT and frequency components ?
Thanks.

If I understood this correctly, you are getting the correct results when outputting to a text file but you are not able to see the results when trying to output to a chart?
This discussion may be of some help to you.
Rob S
Applications Engineer
National Instruments

Array frequency -urgent

Please how do I find frequency number in array. Thank you.

Ah yes its the minus urgent (-urgent) parameter. He should have used the +urgent to turn urgency on.

Seeking Mechatronics Engineering Intern, Santa Clara, CA

Mechatronics Engineering Intern Email resumes to [email protected]
LuxVue Technology is a start up company located in Santa Clara, CA, which opened in September 2011.
We seek an intern who is actively enrolled as a full-time student pursuing an Undergraduate or Graduate Degree in Computer Science, Computer Engineering, Mechatronics or a related filed, at a four- year university. This position will work directly with Luxvue’s team to provide software solutions and support our current project. As a Mechatronics Engineering Intern, you will work directly with Luxvue’s team members to design and implement components that will be a part of larger applications that control our main project that contain one ore more of the following: motors, servos, cameras, pumps, scales, temperature sensing equipment, and interfaces to electronic monitoring devices.
This is a paid internship as a temporary employee for 3 months minimum, 15-20 hours a week.
Our regular business hours are 8-5pm. We are flexible with working around your school schedule as long as it meets business needs.
You will be provided with a fantastic opportunity to gain relevant development experiences by working with multiple groups (software, hardware, mechanical, electrical) in a team environment to provide support to a critical tool at Luxvue.
Submit resumes to: [email protected]
ESSENTIAL DUTIES AND RESPONSBILITIES:
Work independently and in teams to asses project needs, design user interfaces, and control software to meet system goals.
Design, code, debug, document, and support reusable software components using standard OOP practices.
Evaluate third party tools, controls, and components for possible team use.
Work with and support teams (mechanical, electrical, and other engineers).
Use team standard development tools and practices for coding, debugging, and performance analysis and integrity checking.
QUALIFICATIONS:
To perform this job successfully, an individual must be able to perform each essential duty satisfactory. The requirements listed below are representative of the knowledge, skill, and/or ability required. Reasonable accommodations may be made to enable individuals with disabilities to perform essential functions.
REQUIRED:
Level of Junior or above and in good standing at a four-year university as a full-time student pursuing an undergraduate degree in Computer Science, Computer Engineering, Mechatronics, or a related field.
Working knowledge of state machines and object oriented programming
Experience with LabView and/or LabWindows/CVI
Experience with one or more of the following languages: C++, C#, Visual Basic, .NET
DESIRED:
Mechatronics/Robotics/Hardware programming experience (Microprocessors, DSP’s, Motion controllers, PLC’s, etc.)
Exposure to vision systems and image analysis
Experience with Matlab, ActiveX, and Dynamic-Link Libraries
Familiarity with digital control systems, signal processing, filters, FFT, and frequency response analysis
Email resume to [email protected]
Within your resume/application, please also list relevant college courses taken (course numbers and titles). LuxVue Technology provides a friendly and dynamic working environment.

Respected sir/madam,
i am surendra babu.now i am looking for a job
and i have one year experience in LABVIEW.
Herewith i have attach my resume.Please take a look.
if u find any openings on LABVIEW please forward my resume.
Thanks & Regards,
Surendra babu Pidikiti
Attachments:
RESUME-SURENDRA.doc.docx ‏42 KB

Compare Two Waveforms

Hi There,
I would need help in comapring two signals. The Need is to compare a test signal with a reference signal and check if the amplitude of the test signal is within the limits of the reference signal with some tolerence level. Is there any automatic function to DIAdem to get this done.
Can anyone help me out on this.
Thanks,
Priya

Hi Brad,
I tried checking the example but it only gives a graphical display. I would like to compare the actual values and then report status of the test.
This would require to apply known number of time window for the complete Channel; for each time window the channel's amplitude and frequency needs to checked against reference value. If any window does not satify the limits; the test is not passed.
Do you have any kind of example for this approach?
I am thinking of using ChnTimeAreaCopy to get data information for each time window and using FFT for frequency check. I tried using ChnPeakFind for getting the peak values and find the amplidute but was not succesful. Can you help me out on this?
Thanks,
Priya

PCI 4551 for FRA application

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?

Hi Mallesh,
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

Fft find frequency

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