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 Wire-Break Detection in a Two-IDAC, 3-Wire RTD System

Many of the same techniques employed in the previous sections can help identify wire breaks in a two-IDAC, 3-wire RTD system, though there are some corner cases that require special attention. These cases are described in Section 3.2.2.1 (low-side RREF) and Section 3.2.2.2 (high-side RREF).

Regardless if a low-side or high-side RREF is being used, a break in lead 3 automatically eliminates the IDAC path to ground and results in a VREF monitor fault. Figure 3-6 shows how this break occurs in a low-side (left) and high-side (right) RREF configuration. This result is true if any other lead is also broken in addition to lead 3.

GUID-20210107-CA0I-3NXR-8SWG-TNJMZVGVGQSQ-low.gif Figure 3-6 VREF Monitor Fault Detected if Lead 3 Breaks in a Two-IDAC, 3-Wire RTD System Using a Low-Side (Left) and High-Side (Right) RREF

Similarly, if both lead 1 and lead 2 break in either the low-side or high-side RREF configuration, neither IDAC has a path to ground and the result is a VREF monitor fault. Figure 3-7 illustrates how this break occurs in a low-side (left) and high-side (right) RREF configuration.

GUID-20210107-CA0I-8ZVP-MSNX-VRBKV7BCQCT9-low.gif Figure 3-7 VREF Monitor Fault Detected if Lead 1 and Lead 2 Break in a Two-IDAC, 3-Wire RTD System Using a Low-Side (Left) and High-Side (Right) RREF

The challenge in a two IDAC, 3-wire RTD system stems from a break in lead 1 or lead 2. In these cases, one IDAC still has a path to ground, making detection less simple. Moreover, the detection schemes differ depending on if a low-side or high-side RREF configuration is used.