Time data for Frequency Measurement

[DWP]

Hello

I am using Signal Express v4.0 with USB-6210 device to log the frequency of a signal. I am using the 1 counter mode in '1 Sample (On Demand)' mode.  The log I get does not plot the frequency versus time but plots frequency vs iterations.  After doing a few investigations it seems that the number of iterations performed during a measurement is not absolute, but varies according to the input signal frequency, so I don't think I can extract absolute time data from the iteration data. 

Is there a means of plotting frequency versus time, or extracting the time data from the number of iterations?  When I try to run in 'N samples' or 'continuous samples' mode I always get an error.

Thanks

[gt3000]

Hello DWP,

Are you trying to measure the frequency of a periodic Analog Signal using an Analog Input channel?

Or

Are you trying to use the onboard counter to count rising edges on a Digital Pulse Train (square wave)?

Regards,

[DWP]

Hello,

Thanks for the reply.  I am trying to use the onboard counter to count rising edges on a digital pulse train.  The frequency/number of pulses of the pulse train varies with time and I would like to plot this relationship.

Thanks

Dan

[Choover]

Did you find a way to plot time and frequency? I am currently having the exact same problem.

[tronoh]

Dear All

I have plotted waveform graph frequency vs amplitude of real time signal. I am using measurement computing USB1208FS. I used fft.vi to plot the graph and get the waveform which is attached. On X-axis frequency is form 0 to 0.49HZ. But I want to increase that from 50 to 500 hz. When X-axis scale is in auto select mode then it automatically adjust to 0 to 0.499 hz. When I deselect autoselect mode and edit x-axis from 50hz to 500hz then no waveform comes on display. I have set the sapling rate of 1024 and count of 500. Please guide me how can i get the desired waveform graph.

The waveform which i plot is shown in attch1 and my desired waveform is shown in attach2.

waiting for response

Kind Regards

Urfee

[RavensFan]

Wrong forum.

Create a new thread in the LabVIEW forum.

[mavlc]

Hello everybody,

I have also similar problem. I would like to measure frequency with method Large Range With Two Counters. In this case the time interval between two frequency samples also depend on frequency to be measured.

Is there any simple way how to get time data directly from measurent (e.g. using some property node)?

Thanks a lot.

[altenbach]

---

mavlc wrote:

I have also similar problem. I would like to measure frequency with method Large Range With Two Counters. In this case the time interval between two frequency samples also depend on frequency to be measured.

Is there any simple way how to get time data directly from measurent (e.g. using some property node)?

---

 (Property nodes don't do math, they deal with properties.)

I don't understand the second part of the question. Don't you already have time data and want the frequency? The term "time interval between frequency samples" is very confusing!

If you want to analyze an unevenly sampled time data, you can use the Unevenly Sampled Signal Spectrum VI function.

(If you have unevenly sampled frequency data, you can reconstruct the time signal by simply adding the weighted fequencies of all ponts, for example)

EDIT: Sorry, I just noticed that this is the signalexpress forum. I thought this was a LabVIEW question... 

[mavlc]

I am sorry. I thought that this was a LabVIEW question too.

Of course, I am able to compute time data additionaly from measured frequency data.

But if there will be any possibility how to get time data directly from measurement hardware it would be easier. At least I would like to get the time of first frequency sample (t0).

With the term '"time interval between frequency samples" I mean following:

The result of my measurent will be the table with two columns: frequency and time in which the frequency was measured.

Time interval between two frequencies samples is then the difference between two consecutive values in this table.

Finally, i would like to resample this table into waveform because of simpler use.

Thanks a lot

[altenbach]

OK, you apparently only have a single frquency for each time point. That makes the problem trivial. I thought you might be looking for something much more complicated.

It would be so much easier if you could attach a small, but typical dataset.

So, if I understand you right, you have two columns, each row contains a time value and a frequency value. The time values are not spaced equally in time and you want to resample the table such that the time values are linear. How does the desired final time interval relate to the original data? How many more poinst do you want? Do you want simple linear interpolation or something more advanced, such as spline?

You could bundle your two columns and use Resample Pair of Arrays (single shot). Have you tried?

Please attach some typical data and tell us what new time points you want for the output.