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National Instruments Corp.
7
FP-TB-10 Operating Instructions
Dual-Channel I/O Modules
Dual-channel I/O modules are available for current and voltage
input and output, thermocouple and RTD input, and discrete input
and output. This section describes the different modules and shows
how to connect external circuits to them.
Analog Current Input Modules
(FP-AI-C020 and FP-AI-C420)
The FP-AI-C020 and the FP-AI-C420 are dual-channel current
input modules that provide 12-bit-resolution measurements. Each
channel has a programmable filter with two settings, 20 Hz
bandwidth and 100 Hz bandwidth. Each channel has 133
Ω
input
impedance. On the FP-AI-C020, the two channels share a common
reference point (the “b” terminals). On the FP-AI-C420, there is
400 k
Ω
of resistance between 1b and 2b. Wire field devices so that
current flows into the “a” terminals and out of the “b” terminals.
You can use the V and C terminals to connect loop power supplies
and current transmitters.
Note
If your application requires channel-to-channel
isolation, use only one channel of each module.
Figure 7.
Analog Current Input Module Signal Connections
FP-AI-C
xxx
1a
1a
1b
1b
Current
Source
–
+
Loop
Supply
FP-AI-C
xxx
133
Ω
133
Ω
133
Ω
133
Ω
Current
Source
400 k
Ω
(FP-AI-
C420 Only)
2a
2b
2a
2b