Digital Tach on an FPGA

I am trying to implement a simple digital tach onto a machine. Its a proximity switch and a disk with several holes. I want to verify the disk is rotating and don't care (at least for the moment) how fast. I'm using a digital input on my 9074 FPGA and simply want to check for the digital transition over a set time period. Can someone please show me where I can find a sample vi that will accomplish this? Or does someone have a vi they could share?
Thanks
Solved!
Go to Solution.

Hello,
Here is a DevZone with a link to example code for decoding Tachometer signals. Its using Analog Signals, but it shouldn't be hard to change it from analog signals to digital signals. Someone else on the forums may have implemented this with digital however.
Also check out the following Discussion forum.
Regards,
Andrew
Message Edited by Andrew_E on 07-17-2009 11:50 AM
National Instruments
RIO Embedded Hardware PSE
CompactRIO Developers Guide

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Attachments:
host1.png ‏47 KB
fpga1.png ‏131 KB

Posted response to this in the following thread:
http://forums.ni.com/t5/Real-Time-Measurement-and/synchronization-two-fpga-7962r-digital-output/m-p/...
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My first post here.
In the Datasheet and in the examples i was not able to find a solution for my problem:
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Thanks.
Solved!
Go to Solution.

The fastest cRIO analog input module is the 9201, which samples at 500 kHz, which is equivalent to 2 us intervals. That would not be fast enough to catch your pulse.
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Bit of an odd one that had me scratching my head.
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Message Edited by Ralph@NES on 08-21-2007 12:32 PM
Still confused after 8 years.
Attachments:
RPM.vi ‏53 KB

I modified it so that I'm taking 20 samples at 499-501msec. Dividing 60 and 30 (depending on whether it was the cage at two pulses per rev or shaft at one pulse per rev) by this number and getting what appears to be a valid RPM, although my fluctuations are the same or very similar as before. Is there some kind of filtering that I need to do? What am I missing here?
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Attachments:
c.jpg ‏32 KB

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Convert a rpm waveform to digital/analog tach signal. Sound & Vibration

Hello,
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Typically an RPM waveform is the analog view of a tachometer, such as a proximity probe over a key or keyway, or an index pulse from an electric motor. In most rotor dynamics applications, the phase of the tachometer waveform is compared to the phase of other waveforms, such as vibration, to determine the angular position of the shaft when the other waveform occurs.
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[email protected]
www.ni.com/mcm
www.ni.com/soundandvibration
www.ni.com/biganalogdata
512-683-5444

Convert a rpm waveform to digital/analog tach signal. Sound & Vibration

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duplicate post

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Go to Solution.

I have simplified my program to something very basic to replicate the problem.
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Go to Solution.

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Digital Tach on an FPGA

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