Figure 3-11. Pcb Layout For J5 Terminal Block Showing Copper Pours For Cjc Measurement - Texas Instruments ADS1x48EVM User Manual

ADS1x48EVM Overview
The steps for setting up a thermistor measurement with the ADS1x48EVM are summarized below:
1. Connect the sensor to the NTC± terminals on J5
2. Connect an external jumper between NTC+ and REF5025 or REFOUT
3. Populate R14 with a 10-kΩ resistor if necessary
4. Choose the ADC measurement channels to be MUX_SP[2:0] = AIN6 and MUX_SN[2:0] = AIN7
5. Select the ADC reference source to be the same constant voltage output from step #2
3.5.2.1 Using Thermistor RT1 for Thermocouple Cold Junction Compensation
The ADS1x48EVM board includes provisions for using a PCB-mounted thermistor to measure the cold junction
of a thermocouple connected to the TC+ and TC– inputs on J5. As
copper pours create an isothermal bridge between the NTC± and TC± inputs. This bridge helps ensure that
thermistor RT1 measures the same temperature as the thermocouple cold junction at inputs J5:1 and J5:2,
enabling a more accurate thermocouple measurement.

Figure 3-11. PCB Layout for J5 Terminal Block Showing Copper Pours for CJC Measurement

As discussed in Section 3.5.2
ADS1x48EVM. Choose a 10-kΩ NTC thermistor in a 0603 package for this component. To measure the
thermistor voltage, follow the steps outlined at the end of
sensor) is satisfied by soldering the thermistor (RT1) to the PCB. Also, the ADS1x48 is a multiplexed ADC
and therefore can only measure one single-ended or differential input per conversion cycle. As a result, the
thermocouple and CJC measurements must be taken separately and then manipulated in software to determine
the resulting temperature. To learn more about CJC as well as how to use this value to determine the true
measured temperature, see the
16 ADS1x48EVM Evaluation Module
and in Figure 3-9, thermistor RT1 is not populated by default on the
A Basic Guide to Thermocouple Measurements application
Copyright © 2022 Texas Instruments Incorporated
Figure 3-11 shows, top- and bottom-layer
Section 3.5.2, noting that step #1 (connect the
SBAU378A – SEPTEMBER 2021 – REVISED JANUARY 2022
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report.
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