NI 9402 counter function

[GRancourt]

I'm trying to get some clarification on the counter function of my NI 9402 module.  I'm using a cRIO setup with FPGA for the sensors I've already integrated, but for the purposes of troubleshooting the 9402 I've been importing data through the chassis as I would normally do for the cDAQ.  In my LabVIEW project the 9402 appears under the Chassis (9114-cRIO), for reference.

In the project tree, I right-clicked on the 9402 and selected properties then 'Specialty Digital Configuration'.  I changed the inputs to counter type and left the properties under the counter heading as their defaults since I'm interested in counting rising edges. (At the end of all of this I'm going to use the count to calculate an RPM).

The sensor I'm using is an inducting sensor whose output is low enough to merit an amplifier from the manufacturer.  That amplifier converts the signal to a binary-like signal where ~242 mV is the low and ~712 mV is the high.  I assume the counter function on the 9402 will watch for the peaks and count as necessary.

Although I'm ultimately going to use this program in a larger architecture, I've created a small VI designed to test the input of the 9402.  I take the counter value from the 9402 and pass it to a waveform chart and a numerical indicator for redundancy, within a while loop.  When the program runs, the output remains a constant at zero with no noise.

If it helps, I can build an op-amp circuit if my voltage peaks are outside those required for the 9402 but I'd like to avoid that if necessary.  I'm not sure how to get the counter output I require so that's where I need some help.  I'm relatively confident the signal going in is the one I expect since I have a BNC tee splitting the signal between the 9402 and an oscilloscope, but I'm open to connectivity suggestions as well.

Thanks for the help in advance, and if I can provide data sheets, etc. let me know.

Greg

[GRancourt]

I should mention that I've managed to squeeze out 0's and 1's from my sensor to a voltage module, the NI 9205.  The issue there is that I'm missing a ton of peaks showing up on the waveform chart so I don't think it can sample as fast as I need it to even when I don't put a wait VI in the while loop.  If anyone has thoughts going the NI 9205 route and then how to count those peaks that's an acceptable solution and would save me from adding an extra module to the chassis since most of my sensors run out of the NI 9205.

Greg

[Seth_B.]

Hello Greg,

As a digital module, the NI 9402 has very specific voltage level requirements to register a high and a low.  Specifically, the NI 9402 needs the following logic levels (page 9 of the Operating Specifications)

Thus, you voltage level needs to be at least 2V for the module to register a "High" and it needs to drop below 0.8V for the module to be guaranteed to detect a "Low".  You'll need to amplify your signal to be in this range.

Regards,