National Instruments 776572-42 PXI Firewire IEEE 1394 Module 

National Instruments part number 776572-42 is an identifying part number for the SCXI-1142, a Lowpass Filter Input Module with 8-order Bessel Filters and 8 differential Channels. The NI 776572-42 Input module features eight software-controlled input channels designed to amplify and filter signals. Each channel supports an output range of ±5 V and offers independent amplifier gains of 1, 2, 5, 10, 20, 50, and 100. These analog inputs are equipped with overvoltage protection. The module includes lowpass filters with 8th-order elliptic, Bessel, and Butterworth options, all with a selectable cutoff frequency ranging from 10 Hz to 25 kHz, which applies uniformly across all eight channels. Outputs for all channels are accessible via the rear connector. 

The 776572-42 Lowpass Filter Input Module includes calibration hardware designed to eliminate error sources. It features software-programmable analog switches that can ground the inputs of instrumentation amplifiers for offset error calibration using automatic input zeroing. Users can calibrate the module to their specific operating environment by employing an external reference voltage. Additionally, DC compensation circuits eliminate filter offset errors, ensuring precise DC performance even when lowpass filtering is active. The filters in this module combine Switched-Capacitor Filters (SCFs) and continuous-time filters (CTFs). SCF technology enables straightforward software configuration of the cutoff frequency. 

However, SCFs are sampling systems and are susceptible to aliasing effects, similar to digitizers. To mitigate this, the hybrid design incorporates a CTF prefilter to prevent aliasing in the SCF and a CTF postfilter to reconstruct the sampled waveform accurately. To effectively capture data from the SCXI-1142 module, users need to sample it at a rate of 12 times the cutoff frequency, as the stopband begins at six times the cutoff frequency. National Instruments has declared obsolete status for the 776572-42, however it is still available for purchase on the Apex Waves Website.