Switching 2D array for Avg Power Spectrum?

I have a 4 channel 2D array signal which is now indexed so that I can feed 1 channel to the Avg Power Spectrum. It would be much better to have the switching done by radio buttons instead of wired in the Block Diagram. How are the Radio Buttons positioned between a 2D array and the 1D array required by the Avg Power Spectrum?
Regards,
Raymond

I answered your question here. Since the radio button control is just a numeric control, replace your hard coded indexing with a front panel one. Here's a picture of what I mean.
Attachments:
array_indexing.jpg ‏4 KB

Similar Messages

What are the units for the power spectrum output? (units in)^2/Hz?

I can't seem to find the answer in the manual that came with the software or anywhere online. Maybe I am just looking in the wrong places.
Thanks
David

Hi David,
I assume you are referring to the step, "Power Spectrum", in Analysis»Frequency Domain Measurements
Per the help that I see, "This step can return the spectra in root-mean-square, peak, and peak-to-peak
units."
Also, in the configuration tab of the step, for magnitude you can select either dB or linear.
Hope that helps!
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Is possible to use PCI 6250 card for order power spectrum in sound and vibration

Hai all,
Iam new to Labview sound and vibration. In my application i need to extract the order power spectrum, for that iam using PCI 6250 NIcard. I tried with our NI example program i cant able to get the prober result. Whether this card is suitable for my apllication ?. If it is suitable can any one explain to me to get the order power spectrum...
In my application iam using one analog signal and one encoder signal(Speed) . Can any one Help...
Thanks in advance,
Vijay

iam using one accelerometer to get the signal from transaxle gear box. This accelerometer signal iam passing to charge amplifier card to get 0-10v signal. This signal iam passing to PCI6250 ai- 0 channel and encoder is connected with motor is passing to ai-1channel for analog tacho. iam using NI example program (Order power spectrum - analog tacho. VI).
sampling rate is 1000 S/s and no. of samples 1000 for acquiring data. But i cant able to get speed and order magnitude value proberly. Encoder PPR -1000. Can u help me....
Regards,
Vijay.

What is the equation for a Low-Sidelobe Window Function (in Power Spectrum VI)?

I am trying to find out what is the equation for the Low Sidelobe Window which is mentioned in the Power Spectrum VI. Hanning second sidelobe is around -32dB of the first. What is that for Low Sidelobe?

The CWT is not equivalent to the discrete dyadic wavelet transform. In theory, the CWT can compute the wavelet coefficient at any positive real scale and any real shift, while the discrete dyadic wavelet transform only includes the dyadic scales (2,4,8,16...). So the formula used to describe the CWT can be referred to the equation in pp.80 in S. Mallat's book.
In SPT's implementation, the time interval controls the shift in number of samples. The scales indicate the wavelet coefficients at integer scales 1,2,3,...,"scales" are contained in the output scalogram.
NISH DSP
Medical ultrasound and signal processing

Number of cycles using power spectrum for getting frequency

Hi,
I have a square wave that I am getting a frequency estimate from using power and frequency estimate.vi
I was wondering if it mattered how many cycles were inputted for the frequency estimate. Also, the signal may end in between cycles.
Thanks,
Jennifer

Sorry for the vague first post. The software was already written for the device and I am just trying to understand a few things in order to make some changes.
I am measuring the speed of a turning rotor using the square wave signal generated from a pattern on the turning rotor. I need to know the frequency of the square wave in order to determine the speed of the rotor. The pulse pattern is used in power spectrum and estimate frequency icons (appears to be similar to an example program for spectrum analyzer). The speed of the rotor is variable until it reaches steady state which can take minutes or hours. Speeds are not too high (Freq 1-100Hz). Right now the measurement is set up to sample a given number of points at a given scan rate. This means that the data most likely does not end exactly as a pulse cycle ends but somewhere in the middle of a cycle.
We are interested in seeing the transient change in speed from start-up to steady-state. How short of a sampling period (i.e. # of cycles can be put into the power spectrum and estimate frequency.vi's) would give reliable measurments. Right now I just scan for a reasonable time in order to make sure I get enough pulses in order to better estimate the frequency of the pulse signal.
In the future I will work with completing pulse width measurements which most likely would be the fastest I can complete a transient measurement although my data will have a bit more fluctuations. That's due to each pulse not being exactly the same width.
Hope that gives you a better idea what's going on here.

What is the power spectrum unit for Unevenly Sampled Signal Spectrum.vi if the input signal unit is Volts?

The Unevenly Sampled Signal Spectrum.vi has two outputs, Power Spectrum FFT(X) and Power Spectrum FFT(X) Frequency. Can anyone tell me what's the unit for Power Spectrum FFT(X) if the input signal unit is volts. Also, is this VI equivalent to producing a PSD output?

Hi,
The power spectrum will be in units of Vrms^2 which are power units. There is a very usefull VI that you can use to easily transform the units of your spectrum; the VI is called Spectrum Unit Conversion.vi. You select the type of spectrum that you have and the units that you want it to be converted to.
Here is a good document on spectral measurements in genereal:
frequency spectrum
I hope this helps.
Regards,
Juan Carlos
N.I.

Power switch wiring diagram for hp a867c

does anyone know where I can get a diagram for the power switch wire hookup? there are 3 sets of wires labeled hdd led, reset sw, and power led. they plug in on the motherboard on the bottom right corner. they came unhooked and know it will not power up. Thanks in advance

Will this help
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Save Power spectrum

Hi
I would like to save a power spectrum ( about 80000 lines of data) as a file that i can later plot. When i write the cluster (coming out of FFT Powerspewctrum.vi) to an excel (excel works only upt o 56000 or something like that, so i can´t use it anyways) or .txt file using the a combination of open -write -close file i get weird number and letters and not the data i´d like to have. Which data format ( iwould like to make graphs in origin) and vi´s should i use to export the spectrum or is it the best to extract the y-value of the spectrum (magnitude) using the unbundle by name .vi and export it as txt?
Thanks for any help

I believe this is also something i can use for my application, however, when trying to recreate the code in LabVIEW 2011 SP1, the connections between the For Loop and the Close File return an error that the data types are different.The Path wire returns that the source is 1-D array of byte stream file reference with the sink being byte stream file reference. The Error wire returns that the source is 1-D array of cluster of 3 elements with the sink being a cluster of 3 elements. How would i go about fixing this?
I plan on using this to write to the file from an accelerometer connected to a NI-9234 c-series module through a cDAQ-9178 usb chasssis. So my intention is to use this as a subVI to connect the accelerometer signal from the DAQ Assist of another VI. I am trying to record the spectral data. Attached is the attempt at recreating your code.
Attachments:
Save Power Spectrum.vi ‏55 KB

Need Help related to Power Spectrum of two signal

Hello Sir,
I have two signals of different frequencies but i want to take the FFT power spectrum of both signals at same graph . So for that case i take the FFT power spectrum of both signal indivisualy and after this build the array. so i got the one graph and all the components in same graph. Now
The problem is that in that graph i want to extract the magnitudes at each frequency, but when i extract the information from final graph it will be the " 1D array of Cluster of 3 Elements" so its information is saprate for these two signal. but i want to tale the magnitude at each frequency , how can i got this sir . Please Help me
Agnivesh

Sir it works thanks but there is one new problem is that wahen i am going to extract the magnitude for every frequency it is also works, but my question is that if my frequency is in floating point then how can i extract magnitude for that frequency. i mean i extracted the magnitude for every frequency component starting from 0 to 1...2..3...4.............so on (Frequency ) but if my frwquency id 2.3Hz so how can i do this.i am sending you my VI also
Agnivesh
Attachments:
Analysis HP Compressor test 1.vit ‏3485 KB

Power Spectrum

Ok here's the deal.. I acquire data (of type numeric array) from an acuqisition unit (the specifics of it aren't important for the problem) at a known sampling rate and wish to perform a power spectrum on this data. I've used the build waveform function to build a waveform from the 1D array of data with the addition of the dt value (1/Fs) and a timestamp and fed this waveform into the power spectrum vi. The spectrum is then plotted on a waveform chart.
However each time a new data set arrives from the acuqisition unit, the chart is overwritten.I would like to keep the previous data but would prefer not to use shift registers due to the possible size of the array. I thought if the chart's type was a "strip chart" it would hold the data until the buffer is reached but this doesn't seem to be the case.
Another possible issue is with the timestamp but I think I've accounted for that.
Note: The attached vi won't run successfully due to not being connected the the acquisition unit. I was hoping the problem might be clear to someone with more experience using the power spectrum function. I have used it successfully with generic sine waves.
Strokes
Attachments:
Power Spectrum.vi ‏19 KB

Strokes,
you listen to mp3 music from time to time? Maybe, you have configured your application playing those mp3 to display something called "Bars and Waves" (at least, Microsoft calls it like this in Media Player). This display is comparable to an equalizer view.
Your display of the power spectrum analysis is really comparable to this
Does it make sense that the graph does not replace (read: update) instead of "concatenating"?
Norbert
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Expert: Geometry
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Streaming data to disk, need help reading data into Power Spectrum/Octave vi

I'm streaming data to disk in one loop, however once this finishes I'd like to read the data into power spectrum vi/Octave analysis vi in another loop. The data from the read vi is a string and power spectrum vi needs 1d waveform. Does anyone have experience with this process?

From your general description, I gather you are streaming to a text based file (comma or tab separated spreadsheet format) and would like to analyse this data with a power spectrum or octave analysis when you finish. Since you are streaming, I assume you have a lot of data. Do you have more than one channel?
In any case, you have two simple options (and lots of complex ones). You can either read the data back from disk and convert it to a 1D array (try the Read From Spreadsheet File.vi - will get a 2D array, take the first column or the column of your choice if you have more than one channel) or you can use the Spreadsheet String to Array primitive to create an array from your text data before you save it to disk.
If your data rate is slow enough, you can analyze as you acquire and store.
Taking your data as text is very inefficient. What you really want to do is read the data as binary, use that for your analysis, and use something like the Write to Spreadsheet File.vi to save text data to disk.
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Power spectrum density question: One sided convert

Hi, there
I am using the PSD function. In order to get the RMS noise, I integrated the PSD data and doubled the result because I have two sides in positive frequency range and negative frequency range. Then my result is 1.414 (or Sqrt(2)) times higher than my RMS data measured in time domain.
Then I looked into the PSD fuction and found out that in the function of "Convert to on-sided spectrum", the amplitude was doubled. But it is not meantioned in the help file.
My thinking is: either change the help file of PSD function and mention that it is a doubled one-sided output or do not double the amplitude when convert the spectrum from two-sided to one-sided output.
best regards
Chengquan Li
CQ

Dr. Chengquan Li,
I know sometimes the help can be hard to navigate, but I think I found the help documentation that address this issue. It can be found here: Power Spectrum.
Under the heading "Converting a Two-Sided Power Spectrum to a Single-Sided Power Spectrum", you can find the following:
"A two-sided power spectrum displays half the energy at the positive frequency and half the energy at the negative frequency. Therefore, to convert a two-sided spectrum to a single-sided spectrum, you discard the second half of the array and multiply every point except for DC by two, as shown in the following equations."
This is why you noticed that the block diagram of "Convert to One-Sided Spectrum" had the output doubled. I hope this helps clear up the issue.
Regards,
Elizabeth K.
National Instruments | Applications Engineer | www.ni.com/support

How can I use a 1 double array for this

I would like to use one double array where I am using 2 single arrays, can this be done?
thanks
import java.text.NumberFormat;
import java.util.Locale;
class Mortgage3
          public static void main(String[]argv)
          //Variables
          //allows for currency format
          NumberFormat formatter = NumberFormat.getCurrencyInstance(Locale.US);
          double prin;
          double month_payments;
          double monthlyinterest;
                //standard integer
          int months;
                //array for the different interest rates
                double[] interest = {0.0535,0.055,0.0575};
          //array for the different terms
                int[] term = {7, 15, 30};
                for (int i = 0; i < 3; i++)
          //values for the variables
          prin = 200000;        //principle amount of the mortgage
                monthlyinterest = (interest[i] / 12);          //monthly interest
          months = (term[i] * 12);               //total amount of months in the 30 yr term
          //monthly payment calculation
          month_payments = (prin * monthlyinterest) / (1-Math.pow(1 + monthlyinterest, - months));
          System.out.println("\n\n\t For a loan amount of " + formatter.format(prin));
          System.out.println("\t With an annual interest rate of " +interest[i] * 100+ "%,");
          System.out.println("\t your payments will be " +formatter.format(month_payments)+ " per month");
                System.out.println("\t for a term of "+term[i]+ " years or " +months+" months.");
}

I would like to use one double array where I am using 2 single arrays, can this be done?It can, but why not write a Rate class or other data structure more suited to the purpose?

Power Spectrum no longer working correctly after upgrading to 8.0.1

Recently, I installed Labview 8.0.1 to correct a problem I was experiencing in 8.0. The installation resolved my problem, but now the Power Spectrum no longer gives the correct result. My program has not changed other than the update. I checked my circuit and everything is functioning properly. Before changing to 8.0.1 the power spectrum peaked at 40Hz and 80Hz, which was correct, and now it peaks at 0Hz and 10Hz. On top of everything, the peaks are much higher than they should be. I expect peaks with a max of 2.5millivolts and now they are 1volt. I don't understand what is going on. Nothing changed, but the software version. Can someone please help me?

In addtion to Altenbach's comments -
I'd recommend trying another VI function to get the power spectrum for
your signal to see if the behavior is the same. You can find some
examples of VIs using the power spectrum functions using the NI Example
Finder.
You can go to LabVIEW's Example Finder by going to Help >> Find Examples.
Then search for FFT. There should be some results that include FFT and
Power Spectrum Units.vi, Power Spectrum Measurement.vi, Basic Spectral Measurements.vi, and Spectrum Measurements.vi. Try opening and
running these examples to see if the VIs are returning the proper
results.
Mark Walters
Application Engineer
National Instruments

Signal-to-Noise ratio from Power Spectrum?

Hi,
I have a feeling this is a basic issue but for some reason I'm not getting it. I hope this forum can help.
I have a Power Spectrum (freq on the x-axis and power on the y-axis) and I am trying to determine the signal to noist ratio of the rf signal live.
I am using LV 8.5 and have the spectrum toolkit and am using an RFSA in a PXI chassis.
Any suggestions?
Thanks
- rf curious

Hi Rf Curious,
This questions does not have a simple
answer but let me share my thoughts and you can decide what it makes
most sense for your application. For signal to noise ratio (SNR) you
should have ideally the power of the signal and divide it by the power
of the noise. The problem here is that you are looking at both at the
same time (rf live signal). Depending of what type of signal is it, you
can recreate it and substract it from the spectrum (you will need to
recreate the phase and magnitude and delete it from the phase and
magnitude of the spectrum). This is normally done with simple signals
such as a tone.
If you don't have access to the magnitude and
phase of the data, and you only see the spectrum, then you will have to
do things different. You can probably measure the power of the signal
by measuring the power of the band where the signal is located. Then,
you can terminate your input and measure the power of the noise of the
instrument (with same attenuation and RBW settings) and have a rough
estimate. This method should have better results when S >> N. You
can also take the adjacent channel (or further) noise reference.
Finally,
if your signal has a pretty flat spectrum, then you can only take the
difference between the noise and the signal since they both have the
same RBW.
If by now, you have found other methods, feel free to post your ideas here for any other person that come across this problem.
Regards,
Gerardo O.
RF Systems Engineering
National Instruments

Switching 2D array for Avg Power Spectrum?

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