Texas Instruments ADS1x48EVM User Manual page 14

ADS1x48EVM Overview
connect the external jumper between the REFOUT pin (J5:4) and the TC– input to bias the thermocouple output
voltage to 2.048 V. Although this voltage is not equal to AVDD / 2 = 1.65 V, connecting TC– to REFOUT when
AVDD = 3.3 V enables a wider PGA common-mode voltage swing compared to using the REF5025 output. An
external bias voltage can also be directly connected to TC–.
One challenge with the biasing scheme in
break detection. Instead, a separate diagnostic measurement can be made, or the pullup resistor (R24) in
3-7 can be populated to help perform this function. To learn more about different thermocouple biasing schemes
as well as how to measure these sensors with precision ADCs, see the
Measurements application
(CJC), which is used in conjunction with the thermocouple voltage to derive the measured temperature. The
ADS1x48EVM includes provisions for a CJC measurement using a thermistor, which is discussed in more detail
in the next section.
The steps for setting up a thermocouple measurement with the ADS1x48EVM are summarized below:
1. Connect the sensor to the TC± terminals on J5
2. Select a biasing scheme:
a. For pullup and pulldown resistor biasing, populate R24 and R23, respectively
b. For constant voltage biasing:
i. Connect an external jumper between TC– and REF5025 or REFOUT
ii. Apply an external voltage to TC–
3. Choose the ADC measurement channels to be MUX_SP[2:0] = AIN4 and MUX_SN[2:0] = AIN5
4. Select the ADC reference source (REF5025, internal VREF, or external VREF)
14 ADS1x48EVM Evaluation Module
Figure 3-8
report. This document also discusses the need for cold junction compensation
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is that this configuration does not offer continuous wire-
A Basic Guide to Thermocouple
SBAU378A – SEPTEMBER 2021 – REVISED JANUARY 2022
www.ti.com
Figure
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