Using a 9205 to measure RPM

I have not used labview in over 10 years but now have an application that requires but I am more then rusty. I am trying to measure RPM using a 9205 module and I am sure there is a way to do it. I have a pulsed voltage output from my measurement circuit and so far I am capturing the voltage. Can someone suggest a way to convert these voltage pulses to an RPM value. I am sure some type of leading edge counter would work.
Thanks

Not the cheapest route but there is a SCXI card that measures frquency.
http://sine.ni.com/nips/cds/view/p/lang/en/nid/1661
There may be some other frequency cards this is one I have used in the past. With this card you can create a virtual channel and ask it what frequency the analog signal is going into it. From here there is a conversion from frequency to RPM depending on the type of resolver or hall signal you are using to generate that signal.
This method is the easiest but the cheapest would be to get a cheap AI DAQ device that can measure several times faster than the generated signal (nyquist theorem) then analyze the series of AI reads to determine the frequency. Then convert frequency to RPM. Depending on the signal a USB DAQ device might work, if not a PCI or PXI + MXI card would still probably be cheaper than the SCXI route.
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Hi,
please see the following link to NI-Discusion forum. There is simaler question.
http://forums.ni.com/ni/board/message?board.id=110&message.id=1764&requireLogin=False
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SpeedSensorSimulator.vi ‏46 KB
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Finally getting around to this again. My previous post is incorrect, as the code I am using is based on the single period measure (it's right there in the code). I am having a problem with the values returned with this method. Occasionally, the card will return a lower than expected count, resulting in a very large (and incorrect) RPM value. I'm thinking this must have something to do with arming the counter at some unfortunate and coincidental point on the gate signal, resulting in a short count. It must be an unlikely event, because I get thousands of good, consistent values for every one bad one.
To resolve this, I am thinking of going to the single buffered period measurement as suggested above. My idea is to set up a buffer with two values,
and always take the second one (to avoid coincidental arming and short counts). I could also set it up to return more values, and the application could choose the most likely one (ie return three values, throw out the largest and smallest, etc.)
I would rather just use the buffer in continuous mode, since the RPM varies much more slowly than the counter counts, and any snapshot of the buffer at any time would be sufficient, even in the presence of overwriting, etc. This would allow me to arm the counter once and poll it on the fly.
My concern is that in continuous mode, the counter will be throwing a lot of errors which will interefere with the program flow. Can I just set the counter to suppress all errors when I do a buffered read? Worst case, I get a value as it is being written to by the counter, which will have some garbage value (hopefully a recognizable signature) which I can throw out in favor of the other values.
Thanks,
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Attachments:
rpmcircuit.jpg ‏9 KB

If the drawing is right, a pull up seems more reasonable to me
You don't want floating inputs at your cFP.
If the contact opens, the - input floats and need to be pulled to to + input to measure 0V
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Henrik
LV since v3.1
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Measuring rpm using DAQ device

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1. Write a program to read a count every second.
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Using a 9205 to measure RPM

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