Appendix A
Device-Specific Information
©
National Instruments Corporation
A-119
To measure a floating signal source, move the switch to the FS position. To
measure a ground-referenced signal source, move the switch to the GS
position. Figure A-47 shows the AI 0 BNC and corresponding FS/GS
switch on the top panel of the USB-6259 BNC.
Figure A-47.
FS/GS Switch
Figure A-48 shows the analog input circuitry on the USB-6259 BNC.
When the switch is in the FS position, AI
x
– is grounded through a 0.1 µF
capacitor in parallel with a 5 k
Ω
resistor.
Figure A-48.
Analog Input Circuitry
Single-Ended Signals
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-49.
F
S
G
S
AI 0
AI
x +
AI
x –
GS
0.1 µF
5 k
Ω
AI GND
FS
+
–
USB-62
xx Device
Floating Source
AI
x +
AI
x –
GS
0.1 µF
5 k
Ω
AI GND
FS
+
–
USB-62
xx Device
Grounded Source