What is the pass function of the input filter for SCXI AI module?

[abartleson]

I am using Labview with an SCXI1100 chassis. For analog input, I have an 1125 and am adding an 1104C. The DAQ card is a 6052E. The application is ATE for PWM power supplies. Most of the acquisition required is relatively low frequency, however - since the card and the 1104 sample at 333kHz, I should be able to pick up the 20-40kHz gate drive waveforms, and extract frequency, voltage, duty cycle, etc. But here's the question:

The cards themselves have 10kHz lowpass filters. What kind of filters? Chebyshev? Butterworth? Etc. Mathematically, I need to figure what exactly I am going to get out of the card. Is it just going to be attenuated? By how much? What's the noise floor at this frequency?

[John N]

Hello,

The manual on page A-3 has some useful information. I am posting it below. Additionally, I found that the SCXI-1104 series use a two-pole RC Butterworth filter. As you'll see in the notes below the 10kHz cutoff is the -3dB point for the filters.

Filters
Cutoff frequency (?3 dB)
SCXI-1104 ............... 2 Hz
SCXI-1104C ............. 10 kHz
NMR (60 Hz) ............ 40 dB (SCXI-1104)
Step response (either gain)
Accuracy SCXI-1104 SCXI-1104C
To 0.1% 1 s 200 ms
To 0.01% 10 s 1 ms

Hope this helps,

John N
Applications Engineer
National Instruments