SCXI 1140+SCXI 1141 (Sampling and holding filtered signals)

[Frédéric Bonnardot]

Hello,

I have a SCXI 1140 and a SCXI 1141 (Sample and hold - low pass filter) and I
want to use the sample and hold to acquire the filtered data. The user must
be able to choose the cut off frequency with a "text control". My problem is
then to setup the filter cut off frequency without making an acquisition.

The LabView example only show how to acquire the filtered data without using
the sample and hold. I setup the filter like the example (I acquire 10
points that I don't use) and I make the acquisition with the sample and
hold. I works for 1 channel, but if I try to use more chanel
(channels=sc1!md1! 0:1) it don't work (the channel 1 is filtered but the
channel 0 have a constant value).

Do
you have an idea to solve this problem ?
Do you have a simplier method ?

Thank you.

[BruceAmmons]

You need to read Application Note 90, which discusses cascading an 1140 and 1141.

I found an entry in the knowledge base that discusses the application note and updates it slightly. I didn't have any luck finding the app note, so you might want to check with tech support.

http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/ebba33d8d2a3bbd7862566c5007bab1d?OpenDocument

Bruce