2-18
|
ni.com
Chapter 2
Analog Input and Temperature Sensor Measurements
For best results, use the average of at least 100 readings to reduce the effects of noise;
typical absolute accuracies should then be about ±2 °C.
Open Thermocouple Detection
You can build open thermocouple detection circuitry by connecting a high-value resistor
between the positive input and +5 V. A resistor of a few M
Ω
or more is sufficient, but a
high-value resistor allows you to detect an open or defective thermocouple.
Note
Soldering and Desoldering Components on the SCB-68A
Getting Started with the SCB-68A
, for more information about adding
components and for soldering and desoldering instructions.
•
Differential analog input open thermocouple detection
—Use position A to connect a
high-value resistor between the positive input and +5 V. Leave the 0
Ω
resistors at positions
F and G in place for each channel used. Refer to Table 2-1 for component positions for all
analog input channels.
Figure 2-12.
Differential Analog Input Open Thermocouple Detection
AI
i
AI
i
+
8
y
S
C
x
E
A
F
G
B
C
D
+
+
+
–
+ 5 V
AI GND
+ 5 V
AI GND
AI
i
AI
i
+
8
