Frequency/Period measurement with USB-6218

[dicksonc]

I have been trying to get a USB-6218 to measure either frequency or period and have been running in to issues. I have attempted to connected to each counter gate (PFI1 or PFI2) and have not had any luck. I am attempting to meausre lower-frequency signals (1Hz-1KHz) so the Low-Frequency, 1 counter approach seems to be the one I need. The end goal is to get it working in Labwindows. I have made attempts using both sample LabWindows programs as well as MAX. In each of them, it appears that the frequency measurement is actually coming back with the pulse width of both the low and high portions of the signal. For instance, if I am trying to meausre the period of a 100 Hz signal, with a 75% duty cycle, it will toggle between 0.0075 and 0.0025 seconds for the period. If I increase the frequency of the signal to 10 KHz, it measures the frequency well. Is there something I am missing? Based on the manual, I should be able to meausre lower frequency signals using this method. Any help is greatly appreciated.

Thanks.

[HollyBerry]

Can you upload a screenshot of your Task in MAX is setup? Is this happening at all lower frequencies or just at 100 Hz? Lets make sure we can get this working in MAX before adding LabWindows/CVI on top of it.

Sometimes this can happen if the rise/fall time of the signal is not within the specifications of the device. This KnowledgeBase article shows the acceptable rise/fall times.