High-Speed Digitizers

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PXI-5621 and PXI-6602 for encoder-based measurement?

I am evaluating options for an automotive sensor test station.  The sensor will output a waveform corresponding to the proximity of a surface.  It is a speed sensor, so the surface is that of a specialized gear called a tone wheel.  I need to be able to make rise time / fall time / duty cycle measurements and compare them for any given tooth on the wheel through mutiple rotations.  I also need to detect missing teeth or extra teeth. 

To do all that I am looking at the PXI-5621 and PXI-6602.  I am hoping to route the sample clock of the 5621 to the Source of one counter on the 6602.  I will then configure another counter to produce a pulse for each tooth on the tone wheel based on a number of pulses from a rotational encoder on the same shaft as the tone wheel.  The "tooth" pulse would be routed to the Gate of the counter whose Source is the 5621 sample clock.  My goal is to use buffered counter acquisition to latch the sample number of each tooth so that I can go into my waveform from the 5621 and mark off each tooth location.

I must also monitor the RPM of the tone wheel, but I figure I can do that with a third counter timer or make use of the one that is already tied to the encoder.

Does that approach sound viable?  Will I be able to route the sample clock or another representative signal from the 5621 to the 6602?  I require at least 14-bit precision and 20 MS/sec sample rate for these measurements.  Obviously, cost is a big factor as well.

Thank you,

Dan Press
PrimeTest Automation
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I would highly recommend the 5122 over the 5621, which starts at the same price for the base model.  This is because the 5122 has the ability to export its sample clock (the 5621 can not) and at frequencies up to 20 MHz you can route the sample clock through the PXI trigger bus, which eliminates the need for external cabling to the 6602 counter.  Your logic for your counter opperation, seems like the best solution and will work just fine.
Good Luck on your project,
Michael Schneider
National Instruments

Message Edited by Michael S. on 07-22-2005 07:34 AM

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