National Instruments NI SCB-68A, Руководство пользователя

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© National Instruments | 2-19
NI SCB-68A User Manual
• Single-ended analog input open thermocouple detection —Use position A for one
channel and C for the next channel when you 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 2-13. Single-Ended Analog Input Open Thermocouple Detection on AI <i>
If the thermocouple opens, the voltage measured across the input terminals rises to +5 V, a value
much larger than any legitimate thermocouple voltage. You can create a bias current return path
by using a 100 k
Ω
resistor between the negative input and AI GND.
Thermocouple Input Filtering
To reduce noise, you can connect a simple one-pole RC lowpass filter to the analog inputs of the
SCB-68A. Refer to the
One-Pole Lowpass RC Filter section for more information.
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