can pulse measurement.vi measures 2M points with 10ns time interval?

[summerjune]

Hi,

I used pulse measurement.vi to measure the pulse duration of waveforms when the waveforms exceed certain threshold level. The data file has 2 millions data points with 10ns time interval.  But I got error message saying that

"The waveform did not cross the mid reference level enough time to perform this measurement. Check the signal length, mid reference level, and reference level unit."

I was wondering if pulse measurement.vi is capable of handling such large file or it was due to my paramenter errors.

Thank you for your help in advance.

[Dennis_Knutson]

The time interval is no problem and I doubt that the record length is a problem either. What exactly does the waveform look like? Is is a single pulse or are there multiple pulses? Some of the measurements that the VI does will generate the error depending on the data. For example, I don't think it can calculate period or frequency if there is a single pulse.

[summerjune]

Hi Dennis,

There are multiple pulse waveforms. Attached is a waveform shot. I hope you can open it.

What I want to do is measure the pulse duration of the waveform when it exceeds certain threshold level. I have at least thirty waveform data in .txt format that I need to do such analysis. Any suggestion is appreciated.

Thank you.

[Dennis_Knutson]

Since you are only interested in the pulse width, an easy thing to try is to modify Pulse Measurements.VI to only get that reading. You can go to the block diagram and you should see a case statement that is wired to the 'polarity' control. In each of the cases, there is an array of enums that specify a measurement to take. If you delete all elements except for the 'width positive', you can try running it to see if you get the error. If you don't get the error, the pulse width will actually be returned in the period indicator. If this works, you can save the modified VI as a new name and in a new location. You could also make your own Pulse Width Measurement VI by using the subVIs inside. You will need the Close, Create, Fetch, and Clear functions.

[summerjune]

Thanks for the replies. I modified the diagram of Pulse Measurement.vi but I am stil getting the same error.

Possible reason(s):

Analysis:  The waveform did not cross the mid reference level enough times to perform this measurement. Check the signal length, reference levels, and ref level units.

Thanks for your explanation and effort.

[Dennis_Knutson]

I don't have 8.2 so I can't look at the VI. Is it possible for you to post an image of the block diagram. Also, you save a small segment of the waveform and post that?

[summerjune]

I realized that I can't really modify the percent level settings or specfication of the pulse measurement.vi. For instance, I changed the percent level setting to peak instead of the default auto select. After running the VI unsuccessfully and I reopened the pulse measurement.vi, I saw the percent level setting was set to auto select again instead of peak method. I have attached the image of the block digram and a very small part of the waveform data. I hope you can open both.

Thank you.

[Dennis_Knutson]

They say a picture is worth a thousand words.

The way you've written the program, you are only passing two points to the Pulse Measurement function. Two points that are immediately adjacent are not enough to calculate anything. You should be creating a waveform data type and passing the entire waveform to the function. You set the reference levels on the block diagram. Opening the subVI and changing them there does nothing, especially since the Pulse Measurement function is re-entrant.

Message Edited by Dennis Knutson on 02-13-2007 12:33 PM

[summerjune]

Hi Dennis,

Thanks for the picture. But could you explain how you get "external box" (0.00055,0.0004..) wired to the pulse measurement. What are those values and the absolute thing? Or it is possible for you to send me the vi format?

Big thanks.

[Dennis_Knutson]

It's the reference levels input - set to absolute instead of percent. Right click on the input and select Create Constant. I just assumed that you wanted to use absolute instead of percent because I though you wanted pulses only above a certain voltage level.

Message Edited by Dennis Knutson on 02-13-2007 03:56 PM