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Analog Input Lowpass Filtering with an SCB-68 Terminal Block

Hardware: PXI/CompactPCI>>Controllers

Problem:
How do I connect an RC lowpass filter for the analog input channels using an SCB-68 terminal block?

Solution:
Soldering pads are provided on the SCB-68 to build RC lowpass filter circuits for the analog input channels. Refer to the attached file, SCB-68_CircuitDiagram.jpg for the location of the SCB-68 soldering pads used for analog input signal conditioning. Complete the following steps to build an RC lowpass filter circuit:

Single-Ended Lowpass Filter:
  1. Connect the resistor to position Rx(F) for channel CH(i) or to position Rx(G) for channel CH(i+8).
  2. Connect the capacitor to position RCx(B) for channel CH(i) or to position RCx(D) for channel CH(i+8).
  3. Connect the input signal (+) to the appropriate channel on the terminal block and signal (–) to AI GND.
Differential Lowpass Filter:
  1. Connect the resistor to position Rx(F).
  2. Connect the capacitor to position RCx(E).
  3. Connect a short across Rx(G).
  4. Connect the input signal (+) and signal (–) to CH(i) and CH(i+8) locations on the terminal block.
Figure 1 shows the connections for a single-ended and a differential lowpass filter.


Figure 1. RC filter connections


Refer to the SCB-68 User Manual linked below or your hardware documentation for your device pinout.

Note: Filtering increases the settling time of the instrumentation amplifier to the time constant of the filter used. Adding RC filters when scanning channels greatly reduces the practical scanning rate since the instrumentation amplifier settling time can be increased to 10T or longer, where T = (R)(C). You can use RC filters with single-ended or differential inputs.

Related Links:
Product Manuals: SCB-68 68-Pin Shielded Connector Block User Manual (December 2002)

Attachments:


SCB-68_CircuitDiagram.gifSCB-68LPF.gif


Report Date: 08/11/2004
Last Updated: 02/05/2009
Document ID: 3CAI9HPS

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