Conditioning Counter Input in LabView/DAQ Assistant: Hall Effect RPM

[AXN-RXN]

Hi All,

I'm new to LabView and I'm trying to read the RPMs on a training bike. I'm using a USB-6001 Multi-Function DAQ. I've followed some tutorials using the Counter setup with the USB-6001. In a Test Pane (One Sample on Demand), while I'm able to get counts off of the sensor, I'm getting multiple counts for every pass. Say, when the wheel is turning slowly, I'll get 7...15....25...35...etc. So, I'm getting batches of counts on each revolution. I'm thinking that there must be some noise going on. I'm reading about using a Min Pulse Width DAQmx property that may filter out any noise, but I'm not sure how to apply it to the DAQ Assistant or DAQmx.

The circuit to the 3-wire sensor is pretty straight forward. I have ground, +5v in, and signal out. The Signal stays at 5V until the magnet gets close, then drops to zero. I have a 10k-ohm resistor bridging the 5v in and the sensor to pull it up to 5V so there shouldn't be any float.

I'm using the standard Counter example VI attached with the same results as seen in the Test Panel.

Thanks for any help!

[scmave]

The way RPM measurements usually seem to work, is the encoder will output so many pulses per rotation - not just a single pulse every rotation. Do you know what encoder you're reading using the Counter task?

[AXN-RXN]

Damn. Sorry! It is not an encoder, but a Hall-Effect switch. It goes from +5v to zero as the magnet passes. So, each revolution should give me one pulse.

I ended up sensing the Hall Effect switch with an Arduino. The arduino just reads the sensor at a high rate and exports a clean HIGH or LOW digital out signal to my USB-6001 to read. This seems to be working fine for now, but I'd like to figure out if I can use the Min Pulse WIdth property to adjust how the USB-6001 counter reads directly.

[scmave]

I'd imagine you can based on the description in the help file, but I have not had the opportunity to work directly with this property. It's always worth a try!

"Specifies the minimum step TRUE time"

http://zone.ni.com/reference/en-XX/help/371093T-01/nimclvfb/pstepper.minimumpulsewidth_00c200ad/