Measuring Ground-Referenced Signals In Differential Input Mode; Connecting Single-Ended Analog Input Signals - National Instruments BNC-2090A User Manual

Connecting Single-Ended Analog Input Signals

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optical isolators, and isolation amplifiers. The ground reference of a
floating source must be tied to the ground of the DAQ device to establish a
local or on-device reference for the signal.
To provide a return path for the instrumentation amplifier bias currents,
floating sources must have a 10–100 kΩ resistor to AI GND on one input
if DC-coupled, or both inputs if AC-coupled. For more information about
connections to floating signal sources and differential inputs, refer to
E Series User Manual or the M Series User Manual. Refer to the
Bias Resistors section of Chapter 3,
about installing bias resistors.
Measuring Ground-Referenced Signals in
Differential Input Mode
A grounded signal source is connected in some way to the building system
ground; therefore, the signal source is already connected to a common
ground point with respect to the DAQ device (assuming the host computer
is plugged into the same power system). The non-isolated outputs of
instruments and devices that plug into the building power system fall into
this category.
If the DAQ device is configured for differential inputs, ground-referenced
signal sources connected to the BNC-2090A need no special components
added to the BNC-2090A. You can leave the inputs of the BNC-2090A in
the factory-default configuration, with the 0 Ω jumpers in the two series
positions, C and D, as listed in Table 3-1,
Refer to Chapter 3, Signal
signal-conditioning circuitry, such as filters and attenuators, in the
open-component positions.
Complete the following steps to measure a single-ended (SE) analog input
signal.
1. Connect the BNC cable to one of the AI <0..15> BNC connectors on
the front panel.
2. Move the corresponding SE/DIFF switch to the SE position. On the
BNC-2090A front panel, a line indicates which SE/DIFF switch
corresponds to each AI <0..15> BNC connector.
3. Move the RSE/NRSE switch to select how the ground signal is routed.
All single-ended signals share the one RSE/NRSE switch. For more
information about non-referenced single-ended (NRSE) and
Signal Conditioning, for information
Channel Component
Conditioning, for information about building
2-3
Chapter 2 Connecting Signals
Installing
Positions.
BNC-2090A User Manual