BNC-9920 Operating Instructions and Specifications
6
ni.com
AI GND and AI SENSE signals are located at the analog input screw terminals of the BNC-9920.
Measuring Temperature
You can measure temperature on the BNC-9920 with the temperature reference and thermocouple
connector.
To use the integrated circuit (IC) temperature reference on the BNC-9920, move the BNC/Temp. Ref.
switch above the AI 0 BNC to Temp. Ref. The integrated circuit (IC) temperature reference provides
built-in cold-junction compensation (CJC) through software. The IC sensor voltage is linearly
proportional to the sensor temperature where:
°C = Volts
×
100
The sensor is accurate to ±1.5
°
C.
Move the BNC/Thermocouple switch above the AI 1 BNC to Thermocouple. You can connect any type
of thermocouple with a two-prong miniature or subminiature male connector to the thermocouple
connector.
Note
If you are using the NI 9205 in Scan Interface programming mode, unconnected channels can
cause noise on other channels. In order to avoid noisy thermocouple measurements, move the
BNC/Temp. Ref. switch on the BNC-9920 to the Temp. Ref. position.
For more information on thermocouples and CJC, refer to the Developer Zone document,
Taking
Thermocouple Temperature Measurements
, by going to
ni.com/info
and entering the Info Code
rdtttm
.
Measuring Resistance
You can measure resistance with the analog input screw terminals on the BNC-9920. Figure 4 is a
schematic representation of how the BNC-9920 measures resistance.
Figure 4.
Measuring Resistance on the BNC-9920
RES+ is internally connected to AI 3 and V
CC
. RES– is internally connected to AI 11. There is also a
10 k
Ω
resistor between AI 11 and AI GND.
Complete the following steps to measure resistance.
1.
Move the RES/BNC switch above the AI 3 BNC to the RES position.
2.
Configure your software to measure AI 3 and AI 11 in referenced single-ended (RSE) mode.
3.
Connect the resistor to the RES+ and RES– screw terminals.
RE
S
+
AI
3
BNC-9920
V
CC
U
s
er Re
s
i
s
tor
S
crew
Termin
a
l
s
AI 11
AI GND
AI
S
EN
S
E
RE
S
–
AI
10 k
Ω
0.5%
