SBAA483 February   2021 ADS1120 , ADS112C04 , ADS112U04 , ADS114S06 , ADS114S06B , ADS114S08 , ADS114S08B , ADS1220 , ADS122C04 , ADS122U04 , ADS124S06 , ADS124S08 , ADS125H02 , ADS1260 , ADS1261 , ADS1262 , ADS1263

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Features Used to Detect Wire Breaks in RTD Systems
    1. 2.1 Detecting a Wire Break Using a Continuous VREF Monitor
    2. 2.2 Detecting a Wire Break Using a Periodic VREF Monitor
    3. 2.3 Detecting a Wire Break Using Separate Analog Inputs
  5. 3Wire-Break Detection Methods for Different RTD Configurations
    1. 3.1 Wire-Break Detection Using 2-Wire RTDs
    2. 3.2 Wire-Break Detection Using 3-Wire RTDs
      1. 3.2.1 Wire-Break Detection in a One-IDAC, 3-Wire RTD System
        1. 3.2.1.1 Detecting a Break in Lead 2 in a One-IDAC, 3-Wire RTD System
          1. 3.2.1.1.1 Detecting a Break in Lead 2 in a One-IDAC, 3-Wire RTD System Using a High-Side RREF
        2. 3.2.1.2 Wire-Break Detection Summary for a One-IDAC, 3-Wire RTD System
      2. 3.2.2 Wire-Break Detection in a Two-IDAC, 3-Wire RTD System
        1. 3.2.2.1 Detecting Lead 1 or 2 breaks in a two IDAC, 3-wire RTD system using a low-side RREF
        2. 3.2.2.2 Detecting Lead 1 or 2 Breaks in a Two-IDAC, 3-Wire RTD System Using a High-Side RREF
        3. 3.2.2.3 Wire-Break Detection Summary for a Two-IDAC, 3-Wire RTD System
    3. 3.3 Wire-Break Detection in a 4-Wire RTD System
      1. 3.3.1 Detecting Lead 2 and Lead 3 Breaks in a 4-Wire RTD System Using a Low-Side RREF
      2. 3.3.2 Detecting Lead 2 and Lead 3 Breaks in a 4-Wire RTD System Using a High-Side RREF
      3. 3.3.3 Wire-Break Detection Summary for a 4-Wire RTD System
  6. 4Settling Time Considerations for RTD Wire-Break Detection
  7. 5Summary
  8.   A How Integrated PGA Rail Detection Helps Identify Wire Breaks
  9.   B Pseudo-Code for RTD Wire-Break Detection
    1.     B.1 Pseudo-Code for a 2-Wire RTD System (Low-Side or High-Side RREF)
    2.     B.2 Pseudo-Code for a One-IDAC, 3-Wire RTD System (Low-Side or High-Side RREF)
    3.     B.3 Pseudo-Code for a Two-IDAC, 3-Wire RTD System (Low-Side or High-Side RREF)
    4.     B.4 Pseudo-Code for a 4-Wire RTD System (Low-Side or High-Side RREF)

3.2.2.3 Wire-Break Detection Summary for a Two-IDAC, 3-Wire RTD System

Table 3-4 and Table 3-5 summarize the wire-break detection method and expected results for all wire-break conditions using a two-IDAC, 3-wire RTD system with a low-side and high-side RREF, respectively.

Table 3-4 Wire-Break Detection Summary for Two-IDAC, 3-Wire RTD Systems Using a Low-Side RREF
Lead 1 Lead 2 Lead 3 Wire-Break Detection Method and Result
Connected Connected Broken

  • VREF monitor → VREF voltage ≈ 0 V
Connected Broken Connected

  • Disable IDAC1 (connected to lead 1)

  • VREF monitor → VREF voltage ≈ 0 V
Broken Connected Connected

  • Disable IDAC2 (connected to lead 2)

  • VREF monitor → VREF voltage ≈ 0 V
Connected Broken Broken

  • VREF monitor → VREF voltage ≈ 0 V
Broken Connected Broken
Broken Broken Connected
Broken Broken Broken
Table 3-5 Wire-Break Detection Summary for Two-IDAC, 3-Wire RTD Systems Using a High-Side RREF
Lead 1 Lead 2 Lead 3 Wire-Break Detection Method and Result
Connected Connected Broken

  • VREF monitor → VREF voltage ≈ 0 V
Connected Broken Connected

  • IDAC current pulls AINN to AVDD, so VAINN > VAINP and VIN < 0 V
Broken Connected Connected

  • VREF monitor → VREF voltage ≈ 0 V
Connected Broken Broken
Broken Connected Broken
Broken Broken Connected
Broken Broken Broken