Zmod4410 ULP and first data read

I am building a custom PCB with a ZMOD4410 using the 2nd gen ULP library.
After the reply in this thread i have tried to use the ZMOD as follows to further conserve power:

  1. perform calibration (10 samples, 90 seconds apart)
  2. read first data ("11th sample")
  3. perform reset via gpio pin
  4. after one hour (brought down to three minutes during testing), go to 1

However i find that the first received data (point 2) is always the same, even if the sensor is in low air quality conditions. I was under the impression that the first ten readings served to calibrate the device (and thus the first "real" response from the IAQ calculation would return data regarding eCO2 and VOC actually in the air), however this does not seem to be the case.

After trying with the normal measurement method (ie: without the reset and wait), i saw the data (both CO2 and VOC) returned from the IAQ calculation started from the exact same values, but changed with subsequent measurements.

What i'm now wondering is.

  1. what does the calibration actually do, in regards to the first data output?
  2. is the first data output always the same (a sort of "default" value from which to start)?
  3. is it correct to do the calibration-read-reset-wait routine described above in order to conserve power or is the ZMOD sensor (or library) simply not meant to function in such conditions?
  4. if the answer to 3. is that ZMOD/Library is not meant/able to function correctly in the conditions described, are there methods in which i can obtain meaningful eCO2 and TVOC in a way that is overall less power consuming than the intended method of a sample strictly every 90 seconds? (battery life of this PCB is not a secondary concern to the design)

Thanks in advance

  • Hi Isaia, The short answer is, that the sensor is not meant to be used in the described mode (answer to question 3). Changing the timing between the measurements influences the characteristics of the sensing material. The renesas algorithms are trained for a specific operation mode and the timing cannot be changed.

    When the ZMOD4410 is reset, the baseline of ZMOD4410 is reset as well. After power up, the ZMOD4410 needs to see “clean air” event to get accurate measurements. The expected value after startup is “1” for IAQ.

    Baseline Start-Up (Finding the sensor clean air baseline): This time depends on the user environment and when the sensor has seen “clean” air. This can happen in a few seconds but can sometimes takes a few hours. This start-up time overlaps with the other factors (1) and (2) above and is of relevance for all MOx sensors and even for most optical gas sensors. Once the baseline is found, it is saved in our algorithm automatically.

    Note, in all cases the sensor will do a gas measurement and respond to gas changes but it is a matter of accuracy.

    For example, after a quick battery change of a device running in a clean environment, the sensor will report the correct VOC after a few seconds. In case the device was off power for 1+ year and started in polluted air, it may take a day.

    If you would like to talk in any more detail, including specifics related to your application which you might not want to share in public, feel free to raise a ticket (via your myRenesas account) and we can get that directly connected into the sensor team. Thanks JE_REN.