HDC3021: Humidity and Temp Data differences.

Hi Sagar,

Happy to help. I have some follow-up comments and questions from your inputs: 

• "The temperature data fluctuates unpredictably within the chamber and does not align with the Class A sensor readings specified in the datasheet, failing to maintain the required accuracy. The same observations are observed for the Humidity as Well."
  • If the HDC3021 temp measurement is also fluctuating during the tests, then it sounds like the issue is caused by test error. It is very important to ensure that the temp/humidity conditions at any given setpoint are allowed to settle and become uniform within the chamber. If the temp/humidity is fluctuating too fast, or there are temp/humidity gradients inside the chamber (e.g. 1 side of the chamber is warmer than the other), then this will introduce test error and you cannot measure the sensor accuracy. 
  • Test suggestions:
    • Ensure there is enough settling time at each temp/humidity test setpoint. For example we usually spend 30min at each setpoint, however the settling time may depend on your chamber performance. 
    • Ensure the temp/humidity conditions within the chamber are uniform. In our R&D lab, we ensure the humidity chamber calibrated, and we use fans in the humidity chamber to help circulate air and ensure conditions are uniform. 
    • Ensure the reference Rotronic and RTD are placed as close as possible to the sensor.
  • Questions: 
    • What humidity chamber do you use, and is it calibrated? 
    • What is the test procedure? Meaning, what is the sequence/order of temp & humidity set points, and what is the settling time at each setpoint? (For example, we typically test at 30C, sweep humidity from 20% to 80% and then back down to 20% again, in 10% increments with 30 min at each setpoint.)
• "The batch we received was packaged in a polythene bag containing a black container strip. Sensors were placed inside, each topped with pink foam. We ensured compliance with the datasheet's guidelines for temperature, layout, and soldering. After soldering, we removed the pink foam for testing"
  • Did you order the HDC3020 ICs from ti.com or an external vendor? The HDC302x Silicon Users Guide recommends do NOT use anti-static polyethylene bags or packing materials (pink foam/wrap), as these materials emit gases that can affect the sensor.
  • Are you able to take any pictures? 

Some additional questions/comments: 

• Can you please share the data log in an excel format? Including HDC3021 temp & humidity, Rotronic reference temp & humidity, and RTD reference temp. (In the previous post only HDC3021 humidity measurements were provided, and it was pasted directly into the message, so it's difficult to analyze)
• What is the ambient storage humidity in %RH? 
• What do you mean by "PFA"? 
• Please note that the humidity accuracy will change across the temp range. Here is the typical humidity accuracy across the temp range. Min/max accuracy may not be guaranteed at very low/high temps. 
  

Best regards,

Sakeenah Khan

Previous post:

https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/1410093/hdc3021-humidity-data-differences/5399991?tisearch=e2e-sitesearch&keymatch=sagar%20hdc3021#5399991 

Hello Sakeenah, 

Thank you for your response, we reordered the sensors from digikey and as per provided Silicon user guide by you, we will follow the same onwards and let see what will be the result by retest in third party lab. I will provide the data in the Excel format when we test.

Meanwhile can you please provide me the HDC3021 Calibration all reports?

And all test cases and standards that TI follows for calibrate the sensor. 

Please share ASAP.

Hi Sagar,

Our test equipment is calibrated to ISO/IEC 17025 accredited standards (including humidity chamber, chilled mirror, and humidity probe reference).

Here is a suggested test procedure that you can use to evaluate the humidity sensor accuracy. This procedure allows you to measure both the humidity accuracy and hysteresis. Also note the data log should include the following measurements: HDC3021 temperature, HDC3021 humidity, Reference temperature, Reference humidity, Chamber set points, Time stamp.  

1. Acquire a calibrated test setup, including humidity chamber and reference temp/humidity probes, with high uniformity and accuracy. Please note that the reference probe error and any temp/humidity gradients within the chamber will contribute to the total test error. The probe should be placed as close as possible to the HDC3021 sensor. In your case the reference probe is the Rotronic HP22, I am not sure exactly what is the probe's accuracy but I know the Rotronic HP21 has a +/-1%RH error at 18-28C. 
2. Set the test temperature and starting RH, and allow the chamber to settle (e.g. turn the chamber on at 25C, 20%RH and allow to settle for 30-60min; the settling time may depend on your chamber and the test temperature). 
3. Start the humidity sweep for 20-90%RH. 
   1. Start the test at 20%RH 
   2. Up-sweep from 20 to 90%RH by increasing humidity in 10% increments with 30min at each setpoint
   3. Down-sweep from 90 to 20%RH by decreasing humidity in 10% increments with 30min at each setpoint
4. If you need to test another temperature, then return to step 2 and repeat the humidity sweeps. 

Best,

Sakeenah