Measure Frequency with Measurement Studio .NET and C#?

[jonesyjay]

What is the quickest/best way to measure an acquired signal's frequency? Example: Let's say I have a acquired a sine waveform with an analog input channel in C# and measurement studio .net. I have assigned the waveform data to a graph and an array variable. Now what? How do I get what frequency it is? I have used LabView for the last 7 years. Measuring frequency is pretty simple in LabView....just wire up the measure frequency VI. This is done without using any counters....etc. Is there a way to do this in measurements studio.....(NationalInstruments.Analysis......????)

I am using Measurement Studio .NET version 7.1 enterprise, MS Visual Studio .NET 2003, PCI-6071E, SCB-100.

Thanks much all,

Jason

[Adam B.]

Jason,

There actually is not a single function that measures the frequency of an acquired waveform. You can, however, calculate this quite quickly and easily using functions from Measurement Studio. Since frequency is simply one over the period, you can simply calculate the period and then divide. To find the period, you can use the PeakDetector Class. Using the detect method, you can get the position of two successive peaks using the Detect Method, and can subtract the position of these two to find the period. You can then simply calculate the frequency from this. Let me know if you have any other questions regarding this class or method. Have a great day.

Adam B.
Applications Engineer
National Instruments

[jonesyjay]

Thanks much, the technique works!!!

Jason

[E-man]

On using the PeakDetector Class to find frequency, I have a couple question? I have a task to that has 4 AI and outputs a double [,] sampled at 1000 samples/channel. So I get about 4000 samples in data. How do I use the peakdetector class to find the peaks. The example I have on that is not helpful. I have the raw data as a 2 dimentional double array. Let me know if you can help. Thank you

[E-man]

On using the PeakDetector Class to find frequency, I have a couple question? I have a task to that has 4 AI and outputs a double [,] sampled at 1000 samples/channel. So I get about 4000 samples in data. How do I use the peakdetector class to find the peaks. The example I have on that is not helpful. I have the raw data as a 2 dimentional double array. Let me know if you can help. Thank you

[bilalD]

Since the PeakDetector function only takes 1-D array data, you will need to extract the individual rows of data to pass it on to the PeakDetector function. You can use the ArrayOperation.CopyRow if you are using Measurement Studio 7.1. If you using a prior version, check out this link for information on how to do this in C#.

Hope this helps

[E-man]

when you call the method arraySubset(data, row) in the code snippet you provided, what value is passed into row?

[bilalD]

You would provide the row number you are interested in. .NET arrays are 0-indexed, so to extract the first row(or first channel in your case) from a 2D array, pass a 0 to the function.

[dmcintosh]

Peak detection, though, is error-prone when you have multi-tonal signals or the case of low signal-noise. Is there an automated approach using Fourier Analysis (peak of FFT) or auto-correlation built in to Measurement Studio?