speed of a chatterbox

[dsasorin]

Hi. I use Labview 8.6.

I want to measure the speed of chatterbox. It has an optocoupler, so its output it's a voltage. OFF = 0 Vdc, ON = 1Vdc.

So, it is clear that i have a pulse train on output, but the signal isn't rectangular, it has rounded corners. Of course, dimm of the light is the cause of this.

So, my questions is, how to count the pulses. Which function/module should i use ? Maybe a special filter ? which one? I searched for something to help me, but i couldn't find.

[F._Schubert]

Depends a lot on the hardware you are using to measure the signal. An easy way with most NI cards is to use a counter input and DAQmx will directly measure the frequency. But I think they work on 5V TTL signals only.
If you have the raw (analog) signal, you will need to use a trigger function. There are some vi's for this in the palettes. Depending on the noise and distortion of the signal, you might need to use a windowed trigger. Then you iterate over your measurement signal and count the number of triggers found and devide this by the measurement time to obtain the frequency.

Felix

[dsasorin]

I use a cDAQ system with NI-9215 (4 ch. sim. voltage input).So i have the raw analog signal of channel 0.

Thank you, Schubert for your answer. i don't have counter input. What trigger function should i use ? Anyway, i begin to look for it.

I put a screenshot of the signal. Be awere that the amplitude is scalled, it is not voltage. What can i say, noise isn't a problem.

[F._Schubert]

Try this one:

http://zone.ni.com/reference/en-XX/help/371361E-01/lvwave/basic_level_trigger_detect/

Felix