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Selecting analog cutoff frequency for NI-USB 6251

Hello everybody!

 

-I´m trying to acquire voltage analog signals by using a BNC 2110 and a bord NI USB-6251. Does anybody know if a programmable analog lowpass filter is available for NI USB-6251? If it is available, how can I set a value for the analog lowpass filter on labview?

 

thank you in advance,

 

best regards!

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Message 1 of 8
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Duplicate post.  There isn't such a filter though.

 

 

Best Regards,

John Passiak
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Message 2 of 8
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Thank you for this information John Passiak!

 

-If there is no programmable analog lowpass filter for NI-USB 6251, so I will need to use the standart cutoff frequency "fc" of the analog lowpass filter (fc= 750 kHz, as mentioned in the user´s manual) for acquiring my signals. By doing so, it will be necessary to use a sampling rate of at least 1,5 MHz to digitize the signal, in order to avoid aliasing! The maximal sampling rate "fs" available is fs= 1,25MHz (according to the user´s manual). Besides, the duration of the signals which I need to digitize take about 25s. That would lead to a considerably higher number os data, and problems to open and save the signals in Labview!  How can I solve this problem?

 

thank you again for your help!

 

best regards!

 

 

 

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Hi pinguim,

 

You could use a Producer/Consumer design in your application.

http://www.ni.com/white-paper/3023/en/

 

Regards,

Lars

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Hi Lars,

 

-Thank you for the tip! A guess this tip could be a possible solution for handling large amount of acquired data, but would not solve the problem regarding aliasing. What would you say about it?

 

Best regards!

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Hi pinguim,

 

to avoid aliasing you should build a hardware filter at the input of your device. You can't avoid aliasing due a digital filter after A/D conversion.

 

Why Should I Use Anti-Aliasing Filters?

http://digital.ni.com/public.nsf/allkb/68F14E8E26B3D101862569350069E0B9

 

Anti-Aliasing

http://letfdaq2.drupalgardens.com/content/anti-aliasing-ni-article

 

Regards,

Lars

 

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Message 6 of 8
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Hi Lars,

 

-Thank you a lot for the links!

-I know about the problem regarding Aliasing! That´s exaclty the reason why I am looking for a programmable analog lowpass filter for NI USB-6251, as described on my first post!

 

best regards!

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Message 7 of 8
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Hi pinguim,

 

such filters are not available for the NI USB-6251.

Either you build your own low pass filter or you buy other hardware with implemented programmable analog filters.

 

Regards,

Lars

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