SBAA275A June 2018 – March 2023 ADS1120 , ADS112C04 , ADS112U04 , ADS1147 , ADS1148 , ADS114S06 , ADS114S06B , ADS114S08 , ADS114S08B , ADS1220 , ADS122C04 , ADS122U04 , ADS1247 , ADS1248 , ADS124S06 , ADS124S08 , ADS125H02 , ADS1260 , ADS1261 , ADS1262 , ADS1263
For the three-wire measurement, the theory is similar to the three-wire RTD design in Section 2.4. As in the previously mentioned design, two measurements are required. A single IDAC current drives the RTD and two lead resistances. One measurement reads the RTD and one lead resistance and a second measurement measures another lead resistance which is then subtracted from the first measurement.
The ADC makes a measurement from AIN1 to AIN2. This results in the voltage across the RTD and one lead resistance.
A second measurement is taken from AIN2 to AIN4. This results in the voltage across lead 3.
Assuming that the lead resistances are equal, subtract Equation 89 from Equation 88. There resulting measurement is shown in Equation 90.