using counter (6024E DAQ STC)

[Med]

Hi everyone,
i'm very new to Labview and what i want to do is very simple.....but i can't make it work.

I'm trying to count events from an external TTL signal. I have loaded Count edges(DAQ STC).vi. I haven't changed anything in the default parameters so i have:
-counter0
-source is set at PFILine -> default & polarity positive
-gate is set to misc -> Low and polarity negative

I have connected my TTL + signal to PFI8/GPCTR0 and the - signal to DGND. When i start the vi it counts way too much and the count doesn't seem to be correlated in any way with my TTL signal.

The frequency of my ttl signal is very low (<0.5 Hz) and the signal is good (no noise at all).

What am i doing wrong? I have changed the setting from PFIline -> de
faults to PFI8

any help would be really appreciated.

[RIO-Todd]

From your explanation, your connections seem to be OK and you're using the VI correctly. When using the default settings, you should connect your signal to the source of counter 0 (pin 37) and the negative side of your signal to a digital ground.

Is your signal truly a TTL signal? There are certain specifications (rise time, fall time, voltage level, etc..) which the signal must meet to be TTL. I have an E-Series DAQ device and I can run the same program with a slow digital signal and it works perfectly. So, the only thing I would suggest is to make sure that your signal is a digital/TTL signal. The document below goes over the definition of a TTL signal.

I hope this helps.

What Is the Definition of a TTL (Transistor-Transistor Logic) Compatible Signal?

http://digital.ni.com/public.nsf/websearch/ACB4BD7550C4374C86256BFB0067A4BD?OpenDocument

Regards,

Todd D.