NI PXIe-4302/4303 and TB-4302/4302C | © National Instruments | 15
Create a Simulated Device
To run examples without the hardware installed, use an NI-DAQmx simulated device. To create
a simulated device in MAX:
1. Launch MAX.
2. Right click Devices and Interfaces»Create New.
3. From the dialog, select Simulated NI-DAQmx Device or Modular Instrument.
4. Type
4302 or 4303 in the text box at the top of the window.
5. Select the device from the list provided.
6. Click OK.
Cold-Junction Compensation (TB-4302 Only)
The TB-4302 contains a temperature sensor that is used to measure the temperature of the
terminal block for cold-junction compensation, which is performed when computing the
thermocouple temperature measurement.
Cold-junction compensation is the process of measuring the temperature of the screw terminal
junction for the thermocouple and applying a representative compensating temperature to the
temperature measured by the thermocouple channel. The accuracy of the cold-junction
temperature measurement contributes to the accuracy of the overall thermocouple temperature
measurement. The TB-4302 is designed to ensure high-accuracy cold-junction temperature
measurements under a variety of conditions; however, care must be taken to ensure the best
possible accuracy. Refer to the Minimizing Thermal Gradients section for guidelines to
minimize thermal gradients that can impact the CJC accuracy. Refer to the TB-4302 section for
the CJC accuracy specifications.
Minimizing Thermal Gradients
Thermal gradients can be caused by changes in the ambient air temperature near the terminal
block, heat sources from other devices near the terminal block, or by the thermocouple wire if it
conducts heat to or away from the terminal junctions. For optimal CJC accuracy performance,
ensure that changes in ambient temperature and temperature gradients near the terminal block
are kept to a minimum.
Follow these guidelines to minimize thermal gradients that can impact the CJC accuracy:
• Use the smallest gauge thermocouple wire suitable for the application. Smaller wire
transfers less heat to or from the terminal junction.
• Run thermocouple wiring together near the terminal block to keep the wires at the same
temperature.
• Avoid running thermocouple wires near hot or cold objects.
• If you connect any extension wires to thermocouple wires, use wires made of the same
conductive material as the thermocouple wires.
• Minimize adjacent heat sources and air flow across the terminal block.
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