2
connected to a multiplexer, which passes the conditioned signals to the DAQ board or device, or the SCXI bus
in the backplane of the SCXI chassis.
You connect thermocouples to the SCXI-1102 via the SCXI-1303 or SCXI-1300 terminal blocks, which include
an onboard temperature sensor for cold-junction compensation. Alternatively, you can use the TBX-1303 DIN-
rail-mountable terminal block, and cable the TBX-1303 to the SCXI-1102 with a SH96-96 or R96-96 cable.
The SCXI-1303 and TBX-1303 are recommended for thermocouples because they include isothermal
construction, ground-referencing connections for floating thermocouples, and a high-precision cold-junction
sensor.
Thermocouple Measurement Example
For your convenience, a J-type thermocouple wire is included with the SCXI Getting Started Pack. Use this
thermocouple sensor (or substitute your own thermocouple) in the example described in this note.
This section describes step-by-step how to connect the J-type thermocouple to your SCXI system, configure
and install your SCXI module, and take measurements with the thermocouple. The SCXI Application Examples
diskette includes example programs written in LabVIEW, LabWindows/CVI, and C for this application.
Step 1. Connect The Thermocouple
Wire the thermocouple to channel 0 on your SCXI terminal block. For the J-type thermocouple included with
the SCXI Getting Started Pack, connect the positive (white) lead to the positive channel and the negative (red)
lead to the negative channel. Figure 2a shows the thermocouple connection to the SCXI-1303, and Figure 2b
shows the thermocouple connection to the SCXI-1300.
You do not need to connect the negative terminal to ground on the SCXI-1303 because the negative
connection of each channel on the terminal block is already wired to ground through a bias resistor.
Note:
Most thermocouples, like this one, are floating with respect to ground. For floating
thermocouples, the signal connections of Figure 2 are correct. If, however, the
thermocouples that you will use in your application are not floating, but connected to a
ground point, then a) if you are using the SCXI-1303, disable the ground-referencing
circuitry on the SCXI-1303 (see the SCXI-1303 Terminal Block Installation Guide); or b) if
using the SCXI-1300, do not connect the negative lead of the thermocouple to chassis
ground of the SCXI-1300 terminal block. These steps are necessary to prevent the creation
of ground loops.
Summary of Contents for SCXI SCXI-1102
Page 10: ......
