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Chapter 3
SC-2071 Board
© National Instruments Corporation
3-15
SC-207X Series User Manual
Using the SC-2071 Board for Thermocouple Measurements
The maximum voltage level generated by thermocouples is typically a few millivolts. Therefore,
a Lab-NB or Lab-PC with a gain of 100 (the highest possible) should be used for best resolution.
Cold-junction compensation with the SC-2071 board is accurate only if the temperature sensor
reading is close to the actual temperature of the screw terminals. Therefore, when thermocouples
are being read, keep the SC-2071 board away from drafts or other temperature gradients such as
those caused by heaters, radiators, fans, and warm equipment.
Input Filtering and Broken Thermocouple Detection (Optional)
To reduce noise, you can connect a lowpass filter. Refer to Building Lowpass Filters earlier in
this chapter for an explanation of how to design these filters.
Broken thermocouple detection circuitry is built by connecting a high-value resistor between the
positive input and +5 V. The value of this resistor is relatively unimportant; a few megohms or
above works fine. With a high-value resistor, you can detect an open or defective thermocouple.
If the thermocouple opens, the voltage measured across the input terminals rises to +5 V, a value
much larger than any legitimate thermocouple voltage. A sample circuit and the component
placement for a lowpass filter and broken thermocouple detection are shown in Figure 3-13,
assuming that the thermocouple is connected to channel 1.
Summary of Contents for SC-207 Series
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