Low pass filter in LabVIEW Base Development System

[Bacacier63260]

Hello,

I've got a problem for several days and I haven't find even a hint to fix it so it's driving me crazy.

I'm developing an application on LabVIEW Base Development System for automatical aquisition and exploitation of five signals.

These signals are generated by a deformation gauge and four potentiometers linked to a NI USB 6210.

I'm using the DAQ assistant on LabVIEW to get and use these signals.

My problem is that I need a 2nd order low pass filter on the deformation gauge signal to get something I can use afterward and none is include in the Base development Sytem of LabVIEW.

I'm sure there is a way to pass through this without buying the Full Development version but I haven't found it yet.

Does anybody has already had this problem and succeed in fixing it ?

If yes, can I have the code ?

Thanks

[johnsold]

You could start from the transfer function for the filter and write your own VI.

Do you need a specific filter characterstic (you mentioned 2nd order filter)? Would doing some averaging, which is a form of low pass filtering, be adequate for your needs?

Lynn

[DFGray]

Second order low pass filters are not that difficult to write - a convolution will get you there.  You can find the algorithms in many places, but I usually go to the Numerical Recipes site for concise information with just the right amount of detail.

[Bacacier63260]

Thanks for your responses.

I've tried to create a subVI using the transfer function of the filter I need.

Here is the diagram of this subVI :

I'm not sure of this transfer function at all. It seems too simple to me.

Does it look weird to you or does a low-pass second order filter can have such a simple transfer function ?

I've tried it and my signal is still unstable. I guess I'm doing something wrong, but as I'm not that good in electronics, I can't figure out what.

Thanks again

[johnsold]

That is one form of the transfer function for a second order Butterworth filter.

Please post your VI with some typical data along with what you expect the result should be.

Lynn

[Bacacier63260]

Thank you for all your responses but I've change my mind and I'm going to use an hardware solution.

After weeks of search I think there's no possibility to do it on the base version of LabVIEW.

[DFGray]

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After weeks of search I think there's no possibility to do it on the base version of LabVIEW.

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I respectfully beg to differ.  As Lynn reqested, please post your code so we can help you.  I suspect your problem is as related to your hardware as it is to your software.  Let us know if you change your mind.