SNAA427 October   2025 HDC3020

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction: Why RH Sensors Appear Out-of-Spec
    1. 1.1 Where and When do RH Errors Occur?
    2. 1.2 What are the Root Causes of RH Errors?
    3. 1.3 Case Studies
  5. 2Definitions: Key Terms for RH Accuracy
  6. 3Initial Troubleshooting Steps
    1. 3.1 Initial Verification Steps
    2. 3.2 Diagnostic Questions
  7. 4Common Sources of RH Error - Prevention and Mitigation
    1. 4.1 PCB and Enclosure Design Considerations
      1. 4.1.1 PCB Thermal Transfer to RH Sensor
      2. 4.1.2 Power Supply Noise and Analog RH Sensors
      3. 4.1.3 Enclosure Design & Airflow Considerations
    2. 4.2 Assembly, Soldering, and Manufacturing Processes
      1. 4.2.1 Assembly Instructions: What to Avoid
      2. 4.2.2 Assembly Instructions: Best Practices
      3. 4.2.3 Sensor Cavity Protection During Assembly
    3. 4.3 Rehydration Post-Assembly
      1. 4.3.1 Recovering Sensor Accuracy Post-Soldering
      2. 4.3.2 Rehydration Procedure
    4. 4.4 Test Setup and Environment
      1. 4.4.1 RH References
      2. 4.4.2 Setup Uniformity: Controlled Environment
      3. 4.4.3 Setup Uniformity: Thermal Gradients
      4. 4.4.4 Settling Time
    5. 4.5 Storage and Handling
      1. 4.5.1 Storage Temperature and Humidity Conditions
      2. 4.5.2 Storage Materials
      3. 4.5.3 How Does MSL Level Relate to RH Sensors?
      4. 4.5.4 Handling Best Practices
    6. 4.6 Chemical Contamination
      1. 4.6.1 How Chemical Contamination Affects RH Accuracy
      2. 4.6.2 Where and How are Chemical Contaminants Introduced?
      3. 4.6.3 Mitigating Effects of Chemical Contamination: Bake
      4. 4.6.4 Mitigating Effects of Chemical Contamination: Cleaning
      5. 4.6.5 Mitigating Effects of Chemical Contamination: Enclosure Design
      6. 4.6.6 Mitigating Effects of Chemical Contamination: Device Selection
      7. 4.6.7 Mitigating Effects of Chemical Contamination: Assembly Considerations
    7. 4.7 Operating Conditions: Application Environment Conditions and Effects
      1. 4.7.1 Environmental Conditions That Contribute to RH Accuracy Errors
      2. 4.7.2 RH Offset Mitigation & System-Level Design
      3. 4.7.3 Using the Integrated Heater
    8. 4.8 RH Accuracy Debugging Flowchart
  8. 5Summary: Designing for and Debugging RH Accuracy
  9. 6References
  10. 7Appendix
    1. 7.1 Case Study 1: Humidity-Induced Positive RH Offset
    2. 7.2 Case Study 2: Gradual RH Accuracy Drift in 100%RH Environment
    3. 7.3 Case Study 3: Combined Factors from Assembly & Thermal Effects

4.4 Test Setup and Environment

If a user is testing at any point in the engineering process, having a test setup that can test RH sensors as accurately as possible is very important.

RH testing requires:

  1. A calibrated RH & temperature reference sensor
  2. A stable and controlled temperature & humidity environment
  3. Adequate settling time

Without these, measurement noise and RH accuracy errors can occur.