frequency measurement using USB 6008 DAQ

[Miaa]

Hello there,
I am interested in finding out a better way to measure a frequency of a digital signal using USB 6008. Curently, i am using <a href="http://zone.ni.com/devzone/cda/epd/p/id/513" target="_blank">http://zone.ni.com/devzone/cda/epd/p/id/513</a>
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and it seems that its not sensitive engough to detect small changes.
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&nbsp;Has anyone&nbsp; tried a similar measurement. Many thanks and i look froward to your reply with suggestions.
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Thanks

[Dennis Knutson]

Have you tried to do an analog acquisition and using the Extract Single Tone function?

[Miaa]

Kindly, see&nbsp; <a href="http://forums.ni.com/ni/board/message?board.id=40&amp;message.id=6233&amp;jump=true" target="_blank">http://forums.ni.com/ni/board/message?board.id=40&amp;message.id=6233&amp;jump=true</a>&nbsp;and comment on the attached documents. Need your professional advice on this....
PS: Attached is also the manual which describes about counters in chapter 9


621x Manual.pdf:
http://forums.ni.com/attachments/ni/170/324035/1/621x Manual.pdf


value_1.JPG:
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value_2.JPG:
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[Dennis Knutson]

I don't know what you want me to comment on. The ring controls allow you to set the measurement method and the edge of the input signal to start counting on. Do you want to know the difference between the different methods or want to know the difference between rising edge and falling edge?

[Miaa]

Hi Dennis, I am interesetd in finding out how are the numerical values assigned ? Like for rising time, falling time ( as shown in the attached images ).
Kindly, let me know what is the process of calculating these values. Many thanks

[Dennis Knutson]

The values for the ring control have nothing at all to do with a value for a rising or falling time. They are the assigned numeric codes passed&nbsp;of the DAQmx driver to tell it to perform the task. When you use a ring control, what gets passed is the numeric and not the text. Other numeric codes will tell the DAQmx driver to perform something else entirely. If you are curious about the codes, you should look at the NIDAQmx.h file.