How to measure frequency by USB 6211?

Dear all,
I'm using USB 6211 to measure the input analog voltage signal, then use a counter to yield the frequency. Please find the VI figure in the attachement.
The problem is the insteal of measure the right frequency, which is from 300Hz to 1000Hz. There is a lot of high frequency noise from thousand to milliion Hz. I think it pick up the high frequency harmonics. How to avoid it or use a more effective way to achieve the measurements.
Regards,
Alan
Attachments:
flow rate frequency measurement.JPG ‏43 KB

You have to suppress high frequencies on the analog side of your signal. You must set it to a frequency which is not higher than half of your aquisition rate. If you sample with 10 kHz your filter must have a cutoff frequency of max. 5 kHz. Otherwise you will see the signal mirrored at the half of the sample rate. A 6kHz signal will lead to a 4 kHz signal after the sampling.
Waldemar
Using 7.1.1, 8.5.1, 8.6.1, 2009 on XP and RT
Don't forget to give Kudos to good answers and/or questions

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Attachments:
Freq Set Up.jpg ‏2993 KB

So I would select new in "Custom Scaling"
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Hi tintin,
you really should have learned to post good ( read as: meaningful, with sufficient explanations and background information) questions after more than 200 posts in this forum…
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http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=B45EACE3DC9F56A4E034080020E74861&p_node=DZ52325&p_source=External
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HAI..
Im using PFIO line to measure the frequency..i have attached my vi along with this..output is read approximately to the given input when i highlight the execution,but when i use run and run continuosly alone,am getting incorrect values..im totally confused..suggest some ideas..
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Attachments:
counter.vi ‏19 KB

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How to send TTL output AND acquire AI voltage data using USB-6211

Hello,
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Message Edited by Larry_6211 on 12-19-2008 11:24 AM
Attachments:
USB6211_v1.vi ‏212 KB

Hi All,
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Getting Started with NI-DAQmx
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Attachments:
Acq&Graph Voltage-Int Clk.vi ‏37 KB

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Dear kelven,
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Attachments:
autotrain2.vi ‏19 KB

You'd probably get a more coherent answer if you didn't bounce around from thread to thread so much...
How can I generate a pulse train from shaft encoder? (5/13)
pulse train from encoder (5/15)
how to measure rpm (5/20)
How to measure rpm using shaft encoder and labview (5/23)
This thread (also 5/23)
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How to measure frequency by USB 6211?

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