Chapter 4
Connecting and Using Accessories and Transducers
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National Instruments Corporation
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Connector-and-Shell Assemblies
Connector-and-shell assemblies, which are low-cost alternatives to
terminal blocks, have solder pins instead of screw terminals for more
permanent configurations. Connector-and-shell assemblies do not have
strain relief and are made of plastic instead of aluminum. The
connector-and-shell assemblies include the SCXI-1310 and SCXI-1330.
Table 4-1, earlier in this chapter, summarizes the module compatibility for
these connectors.
Connecting Transducers to the SCXI System
National Instruments application software packages include transducer
conversion functions for thermocouples, strain gauges, and RTDs. The
following sections explain how to connect these transducers to the
SCXI system.
Thermocouples
Thermocouples are among the most commonly used transducers. You can
use the SCXI-1100 or the SCXI-1102 to condition up to 32 thermocouple
signals. If you require isolation, you can use the SCXI-1120, the
SCXI-1121, the SCXI-1122, or the SCXI-1125.
Using Thermocouples with the SCXI-1100
If the thermocouple is insulated or not ground-referenced, the
thermocouple produces a floating signal. Therefore, you must
ground-reference the thermocouple. You may acquire inaccurate readings
if you do not use one of the following methods to ground the thermocouple.
Caution
To avoid noise and errors from ground loops, do not reference the thermocouple
to ground at more than one point.
The most convenient way to ground-reference your floating thermocouples
is to use the SCXI-1303, the terminal block which provides a
ground-reference for all 32 input channels. However, if you are using the
SCXI-1300 terminal block, you must connect the negative lead of all your
floating thermocouples to the negative terminal of the input channel and to
chassis ground.
