How I can measure frequency of TTL signal without external clock?

Hello,
I want to measure frequency of TTL signal using PXI-6254 or PXI-6713, without using external clock.
Frequency will be up to 100kHz. How I can use internal counter of 20MHz or 80MHz?

Hi Yuta K,
You have not stated what software you want to use for this measurement, but in case you're using LabVIEW, please go to the Example Finder (in LabVIEW go to "Help >> Find Examples").
In the Example Finder, you make sure the "Browse" tab is stil selected, and than you go to:
Hardware Input and Output >> DAQmx >> Counter Measurements >> Digital Frequency
Here you will find some good examples of measuring a digital frequency with 1 or 2 onboard counters.
If you need additional information, please let us know!
Best regards,
Peter S

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I think I can help out with some of your questions. First, the 1180 module won�t show up in MAX since it is really just a feedthrough cable which allows you access to your unused signals from the DAQ card.
You definitely can measure frequency using your 6024E. An example installs with NI-DAQ 7.2 which shows how to accomplish this. To access this example go to the LabVIEW start up screen and hit the Find Example button. When the Example Finder opens up browse to the following location: Hardware Input and Output -> DAQ -> Counters -> DAQ-STC -> Measure Frequency (DAQ-STC).vi
This example measures frequency and has a connection diagram on the front panel. The documentation for the example can be accessed by going to File -> VI properties -> Document
ation, after you have opened the VI.
You are correct that we offer a frequency input module for SCXI (SCXI-1126). This module would be useful if your input voltages are non-TTL, or if you need to measure more than one channel of frequency signals. This module has an input range of +/- 250Vrms and 8 input channels.
I hope this helps! Let me know if there is anything I can help with or clarify.
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I'm using a National Instruments DAQ board and I need to measure the
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Attached is a vi which models your signal, and provides a way to measure the average frequency over a window of time. It converts the signal to a sequence of periods. I usually start with this approach because you can save the data in a much more compact form if your sampling rate is high. Obviously over a specified period of time, if there are no zero crossings the frequency is zero, so I was a little incoherent before. The real issue is the latency caused by averaging. Your frequency measurement is most accurate half your window size before the current time, so smaller windows give you more up to date measurements, but also more noisy. If you need the most up to date measurement, then you have to use the time since the last crossing which is the case where the frequency never goes to zero. That's probably not a realistic situation. If you needed less latency, you could use a prediction algorithm.
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Attachments:
DigRandFreq.png ‏62 KB
DigitalRandomFreq.vi ‏34 KB

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How I can measure frequency of TTL signal without external clock?

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