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)

3.3.3 Wire-Break Detection Summary for a 4-Wire RTD System

Table 3-6 and Table 3-7 summarize the wire-break detection method and expected results for all wire-break conditions using a 4-wire RTD system with a low-side and high-side RREF, respectively.
Table 3-6 Wire-Break Detection Summary for 4-Wire RTD Systems Using a Low-Side RREF
Lead 1 Lead 2 Lead 3 Lead 4 Wire-Break Detection Method and Result
Connected Connected Connected Broken

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

  • Set IDAC to lead 3

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

  • Set IDAC to lead 2

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

  • Covered by lead 2, lead 3 cases
Broken Connected Connected Connected

  • VREF monitor → VREF voltage ≈ 0 V
Connected Broken Connected Broken
Connected Connected Broken Broken
Broken Connected Connected Broken
Broken Connected Broken Connected
Broken Broken Connected Connected
Connected Broken Broken Broken
Broken Connected Broken Broken
Broken Broken Connected Broken
Broken Broken Broken Connected
Broken Broken Broken Broken
Table 3-7 Wire-Break Detection Summary for 4-Wire RTD Systems Using a High-Side RREF
Lead 1 Lead 2 Lead 3 Lead 4 Wire-Break Detection Method and Result
Connected Connected Connected Broken

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

  • Set IDAC1 to lead 2 and IDAC 2 to lead 3

  • Select internal VREF

  • Change AINx, gain, IDAC magnitude (if necessary)

  • Check conversion result
Connected Broken Connected Connected

  • See broken lead 3 case
Connected Broken Broken Connected
Broken Connected Connected Connected

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