![National Instruments NI 6221 User Manual Download Page 230](http://html1.mh-extra.com/html/national-instruments/ni-6221/ni-6221_user-manual_3441280230.webp)
Appendix A
Device-Specific Information
©
National Instruments Corporation
A-57
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-20 shows the AI 0 BNC and corresponding FS/GS
switch on the top panel of the USB-6229 BNC.
Figure A-20.
FS/GS Switch
Figure A-21 shows the analog input circuitry on the USB-6229 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-21.
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-22.
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