Analog Input Terminal Configurations

The USB-6451 supports three analog input terminal configurations: differential mode, referenced single-ended mode, and non-referenced single-ended mode.

  • Differential mode—The USB-6451 measures the difference in voltage between two AI signals
  • Referenced single-ended (RSE) mode—The USB-6451 measures the voltage of an AI signal relative to AI GND.
  • Non-referenced single-ended (NRSE) mode—The USB-6451 measures the voltage of an AI signal relative to the NR pin (AI SENSE).

    • The AI terminal configuration determines the ground reference for your measurement and affects how you should connect your AI signals to the USB-6451.

    Ground-reference settings are programmed on a per-channel basis. For example, you might configure the USB-6451 to scan 12 channels—four differentially-configured channels and eight single-ended channels.

    The following table shows how signals are routed to the NI programmable gain instrumentation amplifier (NI-PGIA) on the USB-6451.

    Table 17. Signals Routed to the NI-PGIA on the USB-6451
    AI Ground-Reference Settings Signals Routed to the Positive Input of the NI-PGIA (Vin+) Signals Routed to the Negative Input of the NI-PGIA (Vin-)
    RSE AI <0..15> AI GND
    NRSE AI <0..15> NR (AI SENSE)
    Differential AI <0..7> AI <8..15>
    Note You can only include a channel a single time in a given scan. When a specific channel is configured for differential mode, you cannot use the positive or negative inputs from that same channel for referenced single-ended or non-referenced single-ended measurements.
    Note All channels must share the same measurement reference, either referenced single-ended or non-referenced single-ended, when performing single-ended measurements.

    For differential measurements, AI 0 and AI 8 are the positive and negative inputs of differential analog input channel 0.

    Notice The maximum input voltages rating of AI signals with respect to ground (and for signal pairs in differential mode with respect to each other) are listed in the device specifications. Exceeding the maximum input voltage of AI signals distorts the measurement results. Exceeding the maximum input voltage rating can also damage the device and the computer. NI is not liable for any damage resulting from such signal connections. AI ground-reference setting is sometimes referred to as AI terminal configuration.

    USB-6451 Differential Mode Pairs

    • AI <0, 8>
    • AI <1, 9>
    • AI <2, 10>
    • AI <3, 11>
    • AI <4, 12>
    • AI <5, 13>
    • AI <6, 14>
    • AI <7, 15>