National Instruments USB-621 Series User Manual page 171

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• Single-Ended Mode—For each BNC connector that you use for two
single-ended channels, set the source type switch to the GS position.
This setting disconnects the built-in ground reference resistor from the
negative terminal of the BNC connector, allowing the connector to be
used as a single-ended channel, as shown in Figure A-17.
Ground Ref.
Source (GS)
Figure A-17. Single-Ended Channels
When you set the source type to the GS position and configure the
device for single-ended input in software, each BNC connector
provides access to two single-ended channels, AI x and AI x+8. For
example, the BNC connector labeled AI 0 provides access to
single-ended channels AI 0 and AI 8, the BNC connector labeled AI 1
provides access to single-ended channels AI 1 and AI 9, and so on. Up
to 32 single-ended channels are available in single-ended measurement
modes.
For information on how to connect your signals in single-ended mode,
AI GND, and/or AI SENSE, refer to the
Signals on USB-6215/6216/6218 Devices
Input. For a detailed description of each signal, refer to the
Connector Signal Descriptions
LED Information.
Analog Output
You can access analog output signals on the BNC connectors labeled AO 0
and AO 1. Figure A-18 shows the analog output circuitry on the USB-6218
BNC.
Figure A-18. Analog Output Circuitry
Appendix A
+
–
USB-621x BNC Device
section of Chapter 3,
AO x
AO GND
A-25
Device-Specific Information
AI x
AI x+8
Connecting Analog Input
section of Chapter 4,
I/O
Connector and
NI USB-621x User Manual
Analog