Multifunction DAQ

Showing results for 
Search instead for 
Did you mean: 

TTL NI 9401 Edge counting work but not frequency measurement

Go to solution

Hi everyone,


I have a CompactDAQ and a NI9401. I used this hardware with labview to monitor the speed of a crankshaft. My sensor (optics) output a square wave, 0-5v amplitude, TTL compatible.

I have check it on an oscilloscope, it is perfectly well tooth shaped.


 I connect to 9401, and I try these 2 simple .VI in attachement and weirdely,

the edge counting work perfectly, (and the increment speed correspond to the speed of the crankshaft)


But, frequency meserment or pulse with, or period, do not work


Does anybody has a idea why ?


(I struggled during 4 hours and I didn't figure it out)


thank you very much for you help,





Download All
0 Kudos
Message 1 of 8

Have you spent any of that time looking at the specifications? It has no counter so I don't understand how even the first example works.

0 Kudos
Message 2 of 8

It uses the counter of the cDAQ (it has four counter !)


0 Kudos
Message 3 of 8

Sorry, did not know that about the cDAQ.


Have you run the example called Meas Dig Frequency-Low Freq 1 Ctr? I am not that familiar with cDAQ but you should check to see if the default source connections for frequency are the same as for counting edges.

0 Kudos
Message 4 of 8

thank you very much for your answer,


I'm not able to check if the example vi works until tomorow unfortunately,

but I'm quite pessimistic...




0 Kudos
Message 5 of 8
Accepted by topic author gdlbb

Hey, I found my problem,


I need to plug the wire into line 5 instead of 4

I choose ctr1 for instance, and then edge counting work ONLY on number 4 and frequency, period measuremnt etc work only on line 5.

tricky for me.




0 Kudos
Message 6 of 8
Which is why I mentioned that you should check the default source connections. The source connections are something you can change.
0 Kudos
Message 7 of 8

Indeed, I will try to do that to be able to genreate 3 pwm on 3 different lines, not at the same time, using the same counter.

I found this example, and I will try to run/adapt it on my CompactDAQ : 





0 Kudos
Message 8 of 8