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SVT weighting filters... arbitrary rate works but fixed rate doesn't

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Hi, I am quite a new user to LabView, but am slowly getting the hang of it through tutorials and help!

I have found that if I feed a waveform channel into a "SVT A,B,C Weighting filter" VI, I get the result I expect with the "arbitrary" rate version of the filter, but no filtering seems to be applied if I use the "fixed" rate version.

The data is originally coming from a DAQ Assistant VI express, at 10kHz.  This is a standard sample rate (as listed in the NI guidance article here), so I'm not sure why it should not work.

Whilst I have it working okay with the arbitrary rate version of the filter, it is good practice to use the "fixed" version, and I am also trying to understand why things are the way they are...

Thanks if anyone can shed any light on this!

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Hey Sideburnz,

 

I was wondering if you could please clarify in a bit more detail what you meant by not getting the result you expected?

 

As it specifies in the manual you sent me earlier on, the algortihms which are designed for the fixed and arbitrary weighting approaches are different. Hence, when filtering a frequency at the same frequency but using different methods, you can expect to yield different results. 

Could you perhaps attach the code you are using and also explain a bit more about the hardware you are interfacing with?

 

Kind Regards,

 

Will

 

Applications Engineering

National Instruments UK 

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Thanks very much for your reply.  No, it's not just that there are 'differences'... the fixed version of the filter is not filtering at all!  I have simplified my VI and attached it.  I am using a cDAQ as input.  As I said, the DAQ Assistant VI is set to continuously acquire at 10kHz (with a 100ms buffer).

Thanks!

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No problem!

 

I not managed to replicate your issue as of yet, could you perhaps send through the screenshot of the signal you are unhappy with?

Have you tried any other signal frequencies to see if the same result occurs at all?

 

Best,

 

Will 

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Accepted by topic author sideburnz

It's okay, I've finally found the answer!  It has only just dawned on me that only specific sample rates are supported by the hardware, and whilst I was entering 10kHz in the DAQ Assistant, I now realise that it was actually giving me 10240Hz, which is not a "standard" sample rate as far as the fixed filter is concerned.

It all makes sense now, and I learnt something new.

Thanks for your help 🙂

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