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National Instruments Corporation
13
TBX-1303 32-Channel Isothermal Terminal Block
Table 4 shows which resistor networks to use for the SCXI module, signal
type, and application.
Caution
Connecting an external ground-referenced signal with the 10
Ω
resistor network
in place can cause permanent damage to the resistor network and the traces on the
TBX-1303 printed circuit board. NI is
not
liable for any damage or injuries resulting from
improper signal connections.
Detecting Open Thermocouples
To detect an open thermocouple, check whether the corresponding SCXI
module channel is saturated. The pull-up and bias resistors on the
TBX-1303 saturate the channel by ap5 V at the input of an open
channel, and the positive rail saturates.
SCXI-1102/B/C Module
You can replace the 10
Ω
bias resistor networks (factory-default
configuration) in the TBX-1303 with the 10 M
Ω
resistor networks
supplied in the kit. Using the 10 M
Ω
resistor networks, you can have
ground-referenced or floating signals. The channels with open
thermocouples saturate at all sample rates of the module.
Table 4.
Selecting the Appropriate Resistor Networks
Module
Bias
Resistor
Pull-up
Resistor
Source
Impedance
Signal
(Floating or
Ground-
Referenced)
Open
Thermocouple
Detection
Comments
SCXI-1102/B/C
10 M
Ω
10 M
Ω
Low
Both
Yes
Recommended
configuration
for the
SCXI-1102/B/C
10
Ω
10 M
Ω
Low
Floating
Yes
Factory-default
configuration
10
Ω
None
High or low
Floating
No
—
None
None
High or low
Ground-referenced
No
—
SCXI-1100
10 M
Ω
10 M
Ω
—
—
—
Not
recommended
10
Ω
10 M
Ω
Low
Floating
Yes
Factory-default
configuration
10
Ω
None
High or low
Floating
No
—
None
None
High or low
Ground-referenced
No
—
Low source impedance:
≤
50
Ω
High source impedance: >50
Ω