Connecting Analog Input Signals; Connecting Differential Analog Input Signals; Measuring Floating Signals - National Instruments BNC-2120 Installation Manual

5. Test specific device functionality, such as the ability to send and receive data with MAX test panels.
Refer to the DAQ Getting Started Guide for detailed information about running test panels in
MAX.
When you have finished using the BNC-2120, power off any external signals connected to the
BNC-2120 before you power off your computer.

Connecting Analog Input Signals

You can use the analog input BNCs on the BNC-2120 in the following ways:
• Measure differential AI signals, as described in the Connecting Differential Analog Input Signals
section
• Measure temperature, as described in the
• Measure resistance, as described in the

Connecting Differential Analog Input Signals

Use the BNC-2120 BNC connectors on the front panel to connect AI <0..7> signals to your DAQ device.
The BNC-2120 is only intended for differential analog input signals. The number of connectors you use
depends on your DAQ device and application. Complete the following steps to measure a differential
(DIFF) analog input signal.
1. Connect the BNC cable to one of the AI <0..7> BNC connectors on the front panel.
2. If you are using AI 0, move the BNC/Temp. Ref. switch to the BNC position.
If you are using AI 1, move the BNC/Thermocouple switch to the BNC position.
If you are using AI 3, move the RES/BNC switch to the BNC position.
3. Configure your software to measure the channel differentially.
4. Move the FS/GS switch to the applicable position, depending on whether you are measuring a
floating source (FS) or ground-referenced source (GS) analog input signal. Refer to the Measuring
Floating Signals and
these signal sources.

Measuring Floating Signals

To measure floating signal sources, move the corresponding switch below the BNC connector to the FS
position. In the floating source switch position, the DAQ device's amplifier negative terminal connects
to ground through a 4.99 kΩ resistor, as shown in Figure 2. Refer to your DAQ device documentation
for more information about measuring floating signals.
1
When using the BNC-2120 with Connector 1 of NI 6224/6229/6254/6259/6284/6289 devices, the AI <0..7> BNCs on the
BNC-2120 map to the AI <16..23> channels on the M Series device.
© National Instruments Corporation
Measuring Temperature
Measuring Resistance
Measuring Ground-Referenced Signals
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BNC-2120 Installation Guide