ZMOD4410 testing conditions and environment compensation

Question

dear team, 
 
 thanks for a promising product so far. 
 my goal is to determine human presence in the room using co2 as a proxy. This is why i'm interested in the eCO2 from ZMOD 4410. I Understand the gas sensor is not an NDIR CO2 sensor and will not measure actual CO2, yet I'd hope it would be close enough. 
 
 I've been running 3.2.0 library and sensor is providing results. 
 unfortunately the figures do not seem to correlate with human presence in the room. I know that there will be a delay of at least 15-30 min for the sensor to react. sensor is running for more than 48h so this is why I'd need your help. Please find a few hints about the setup so far. 
 Is there a testing procedure to ensure that sensor is actually ok, It would be very helpful for you to share a test procedure to confirm that readings in specific test conditions are correct: for example controlled conditions can be based on salt and ethanol concentration in containers. This would help understand whether the sensor is working correctly and we can compare results with factory results. 
 secondly, I understand there is temperature compensation if we provide temperature. Can you help us understand how important temperature compensation is, especially if variation is 'small' in the ambient air , e.g. between 23 and 28 deg. finally, I see there is new firmware 4.2.0. I have still rouble to upgrade, but can you indicate if v4.2.0. will be substiantially better at evaluating e-c02 ? based on release notes, it seems there is no major improvement with v4.2.0. Thanks again for your help as sensor seems very promising.

IK_Renesas · Answer

Hello, 
 Thanks for reaching out Renesas Engineering Community! 
 As far I can understand you are mentioning that the eCO2 concentrations do not correspond to the fact that there is human presence in the room or not? 
 1. Can you please share with us which MCU target you are using to be sure that you use the correct precompiled libraries for the 2nd IAQ Gen operation mode? 
 2. You mentioned that you left the sensor been working for 48 hours. That's is correct since these sensors are MOX sensors for proper initialization we suggest to leave the sensors constantly been taking measurements for the very first power-on for at least 48 hours. And after this period passes we suggest to start evaluating the sensor measurements. 
 Please be aware that initially the sensor for some time needs to be placed in an enviroment with "clean air conditions" for some time from the very first power on, so that you will give to the sensor enough time to calculate the baseline resistor value which will be stored for the algorithm and will be used as the reference resistance value for clean air. When we mention clean air we mean a room, which is not crowded with people and there is good air ventilation (e.g. open windows). 
 Have you done this? Have you left the sensor working for a while in clean air conditions, so that it calculated correctly the baseline resistance value? 
 3. Your observation about temperature and humidity is correct. The temperature and humidity will have impact on the final readings. As these sensor are MOX sensors and the behavior of the MOX layer is changing depending the temperature and the humidity measured. So for better accuracy for your results it would be good to have an extra temperature plus humidity sensor in order to feed to the algorithm these data as inputs and have finally better accuracy in the results the algorithm outputs. 
 4. In general we recommend to our customers to use also our Evaluation kits with our sensors. Which have already been stabilized by us, since they have been left working in the factory for 96 hours. And they can be used with a GUI SW provided by us that will give the final measurement results. And also you have the ability to save the measurements in .csv log files to compare with your device measurements. 
 Here is our EK for ZMOD4410: https://www.renesas.com/en/products/sensor-products/environmental-sensors/zmod4410-evk-indoor-air-quality-sensor-evaluation-kit 
 And as you can see it has extra HS4001 (temp &hum) sensor on the sensor daughter board: 
 
 So you could initially request a sample from our website for this to use it as reference and start comparing your device measurements with those the EK with sensor board provides. 
 5. I would suggest that it would be good to use the new version of the library since some improvements have been done as far it concerns reducing the noise with lower gas concentrations. And always the latest versions are improved and suggested to be used. So yes I would suggest to go from 3.2.0 to 4.2.0 version. 
 https://www.renesas.com/en/document/swo/zmod4410-iaq-and-tvoc-firmware-2nd-generation-algorithms-iaq-2nd-gen-recommended-new-designs?r=454426 
 
 Please make sure that as soon as you switch to the new library version you leave the sensor been working in the beginning for some time to clean air so that it can calculate correctly the baseline resistor. And also make sure you leave it being working for 48 hours ( and more if possible e.g. 96 hours). And then start evaluating the measurements. In your case where you are switching to new library version to be sure that you are in the "safe side" to start evaluating measurement more than 48 hours being working is better. 
 In general we do not suggest powering of the sensor, since for as long as the sensor has been left power on and working the more accurate the measurement results will be. And also in case it gets powered off for a while the less typical start up time it needs if it has worked for a long time period. 
 Even in applications where low power consumption is a requirement, we do not suggest powering-off the sensor. 
 
 Now as far it concerns the comparison between our sensor which is a MOX sensor and gives the estimated CO2 values and compared with the NDIR sensors which provide the absolute CO2 value, please let me inform you that we have a report published. Based on tests which run for two months where the performance of our sensor is compared with other NDIR sensors in the market and the final results showed that our sensor can give quite good results as the NDIR sensor. Here is the report if you would like to have a look: 
 https://www.renesas.com/en/document/rep/ksi-report-evaluation-renesas-eco2-solution-full-test-report?r=454426 
 
 Also, I think it would be good to share with us some measurements to check your sensor behavior while the room you are testing is crowded. 
 Do the RMOX resistance value gets decreased while the room is getting more crowded? 
 
 Hope it helps. 
 
 Best Regards, 
 IK