measure a 20Hz TTL signal frequently

[c.r.]

Hello,
I need to calculate the frequency of a TTL signal (0 to 100Hz) very often, in order to record it. I'm looking for a way to obtain this frequency as often as possible, with a 2 digit precision. I've not find out how to do from the NI examples.
Any idea will be welcome.
Thanks.

[Brent_R]

Hello,

The best tool for this measurment would probably be one of our TIO-based counter boards, such as the 660x. The operation you need to perform is a "buffered period measurement", in which the card will return the time between each TTL pulse and you can easily calculate a frequency. The TIO boards use an 80MHz timebase that will give you a period resolution of ~12.5ns.

The TIO boards use the NI-DAQ driver. This driver includes several example programs for performing period measurement in various programming environments (LabVIEW, VB, VC++).

Regards,

Brent R.
Applications Engineer
National Instruments

[cr]

thanks. I'll have a look on this card. Nevertheless, I've a PCI 6023E.I hope I can do the same with that card which has 2 counters. Perhaps I have to find a buffered period measurement example in order to understand if I can got the frequency every half a second.
Let me know if I'm in the bad way.

regards.

Christophe

[DFGray]

If you have LV6.1 or later, you can use Pulse Measurements.vi on a waveform to get the data you want. Alternately, you should be able to use the counters on your board to get two digits of accuracy on a 100Hz signal. You will need to run the counters at 10kHz or higher. The higher you run them, the more accurate they will be, up to the accuracy of the on-board or reference clock.

[c.r.]

Yes, I've find a very good and easy way to do, via the example : ftp://ftp.ni.com/contrib/epd/B45EACE3E29A56A4E034080020E74861/Measure%20Period-Easy%20(DAQ-STC).zip

I'm not sure that the link is clickable. Anymay, just note the name of the file :
"Measure Period-Easy (DAQ-STC).zip"
It's not a good idea to have blank in filenames...

[Brent_R]

I didn't realize you already had the E series card and that "fast" meant only every half second. In this case the STC based counters shoud be just fine.

Regards,
Brent