USB-4431 Feature Usage

102.4 kS/s, 100 dB, 0.8 Hz AC/DC Coupled, 4-Input/1-Output Sound and Vibration Device

  • 4 analog input channels; ±10 V; 102.4 kS/s simultaneous sampling rate
  • 1 analog output channel; ±3.5 V; 96 kS/s update rate
  • 24-bit resolution for good signal to noise ratio on AI channels
  • Software-selectable IEPE signal conditioning (0 or 2.1 mA)

USB-4431 Pinout

Front Panel


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Back Panel


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Table 1. Signal Descriptions
Signal Reference Description

AI <0..3>+, AI <0..3>-

Analog Input ChannelAI+ and AI- are the positive and negative inputs of the pseudodifferential analog channel.

AO 0+, AO 0-

Analog Output ChannelAO+ and AO- are the positive and negative outputs of the pseudodifferential analog channel.

PFI <0..7>

GND

Programmable Function Interface—A digital trigger input.

GND

Ground—Ground reference for the PFI inputs.

Table 2. LED State/Device Status
POWER ACTIVE Device Status
Off Off Device is not powered.
On Off Device is configured, but there is no activity over the bus.
On On Device is configured and there is activity over the bus.

Block Diagram

The following figure shows the USB-4431 block diagram.

Figure 1. USB-4431 Block Diagram

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Analog Input Features

The following figure shows the USB-4431 analog input circuitry block diagram.

Figure 2. Analog Input Block Diagram

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The USB-4431 analog input channels feature the following:

  • Sampling rates up to 102.4 kS/s
  • Input voltage range of ±10 V pk
  • Per channel AC or DC coupling
  • Per channel selectable IEPE current excitation on channels 0..3
  • Overload detection
  • Anti-alias filtering
  • Multiple triggering modes, including external digital triggering
Note When there is no sensor or source connected to a channel configured in DC coupling, it will read approximately 2 V to 2.5 V.

Analog Output Features

The following figure shows the USB-4431 analog output circuitry block diagram.

Figure 3. Analog Output Block Diagram

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The USB-4431 analog output channels feature the following:

  • Update rates to 96 kS/s
  • Output voltage range of ±3.5 V pk
  • Anti-image filtering
  • External digital triggering
  • Onboard waveform regeneration
  • Onboard interpolation filtering

Anti-Aliasing Filter Response

The following figure shows the digital filter input frequency response.

Figure 4. Digital Filter Input Frequency Response

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The following figures show the response of the analog input filters. Since the digital filter lets through narrow bands of frequencies at multiples of 64 fs, it is necessary to use the previous figure to know how much attenuation is received by signals in these bands.

For example, when sampling at 51.2 kS/s, the digital filter will remove any out-of-bandwidth tones up until a 51.2 kHz band centered on 64 fs, or 3.2768 MHz ±25.6 kHz. If noise in the input signal falls into this narrow window, the noise is not rejected by the digital filter. In this limited frequency range, you must consider the analog filter. The analog filter on the USB-4431 has an attenuation of 62 dB at 3.2768 MHz. Therefore, the worst-case alias rejection is 62 dB in this example.

This situation represents the worst-case alias rejections for a sampling rate of 51.2 kS/s. You would only observe this worst-case scenario with a well-defined tone in a narrow frequency range. In real measurement situations, it is more likely that any energy passing the digital filter consists only of low-amplitude noise. If an unwanted component does appear in the digitized signal, increasing the sampling rate might provide an easy solution by both improving the rejection from the analog filter and by repositioning the digital filter so that it can eliminate the alias.

Figure 5. Analog Filter Input Frequency Response

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