USB6009 Digital Input : Problem to acquire logic signal

[Minikisscool]

Hi,

I need to acquire 3 signals.
I use Digital Input from USB6009

2 signals (P0.0 & P0.3) are periodic square 180µs (UP then down)
The third signal (P0.2) is not periodic but has High Level during 90µs then low level during approx. 100ms.

With my program, I never see high state from non-periodic signal.
Is it normal ?

[Minikisscool]

I think that I have the explanation

By setting the sampling rate the time between two samples is defined and can be calculated by

 [sample interval] = 1 / [sampling rate]. Examples:

Sampling rate 50 kS/s ; sample interval between two samples = 1 / 50 E3 =  0,02 E-3s = 0,02ms = 20µs

Sampling rate 100 kS/s ; sample interval between two samples = 1/ 100 E3 = 0,01 E-3s = 0,01ms = 10 µs

Sampling rate 1 MS/s ; sample interval between two samples = 1/ 1 E6 = 1 E-6s = 10 µs


Sample rate of USB 6009 is not enough ?

[pierre.denis · Accepted solution]

Hello Minikisscool,

Thank you for posting to National Instruments' forum.

You should consider having a look on the Nyquist frequency to understand the needs of your application.

Then go have a look on the specification of your DAQ Device: NI-USB-6008/6009  and USB 6009

Your card has just one counter at a maximum rate of 5MHz. if you want to count at the full speed (and it might be the case considering your input rate), you can count just one channel with hardware timing. You can count the 4 other channels but with a software timed clock limited to 1KHz (1ms). This exemple show how to implement Digital Input with Software Timed: Example DI Software Timed

Best regards