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1. Is the XENSIV^TM PAS CO2 sensor affected by acoustic and vibration noise?
   XENSIV^TM PAS CO₂ sensor has a robust packaging, and is acoustically isolated from the surrounding noise. The sensor has been designed in such a way that only CO₂ molecules can diffuse within the measurement chamber, while significantly attenuating the surrounding noise. As shown in Figure 1, the sensor performance remains within the specifications up to 101 dB SPL for pink noise, which is one of the most common signals in biological systems and is widely present in modern-day music.
   Figure 1. Acoustic robustness of XENSIV^TM PAS CO₂
   
   

   Infineon recommends that you isolate the sensor from vibration sources. The operating frequency of the sensor is 40 Hz. If vibration is expected at exactly 40 Hz with very high acceleration (≤ 0.3 g), you should do the following to minimize the vibration impact:

   • Mount the sensor in the X-direction of vibration.
   • Enable the denoiser filter.
   • Operate the sensor in continuous mode.

However, for a typical application, the impact of vibration is minimal. As shown in Figure 2, for a test setup with three sensors mounted on a commercially available air purifier, the test result shows that with the denoiser filter enabled, the sensor is robust against the vibration generated by a different fan of the air purifier.

 Figure 2. Vibration robustness of XENSIV^TM PAS CO₂

For more details, visit the CO₂ sensor website and see the application note, General design in guidelines for XENSIV™ PAS CO2 sensor.

2. How much indoor area can be covered by one sensor for a typical application?
   Even though CO₂ is generated locally, after a certain period, the CO₂ concentration is distributed throughout the room. Therefore, irrespective of the room size and number of people, the sensor is capable of accurately estimating the indoor CO₂ concentration within an indoor environment. For more details, see the application note, General design in guidelines for XENSIV™ PAS CO2 sensor.
   
   
3. Are scientific literature available indicating the harmful effects of CO₂ for human body?
   Several studies have been done on the effect of CO₂ on the human body at various concentration levels. The summary is provided in the chart. See Source [1] for the details of the study.
   
   

   Figure 3. Impact of CO₂ on the human body at various concentration levels

   Source
   

   1. https://www.sciencedirect.com/science/article/pii/S0160412018312807
   2. https://books.google.de/books?hl=en&lr=&id=TEnO6lILSj4C&oi=fnd&pg=PR8&dq=Co2+sensors+and+health&ots=Xy1umDNsmq&sig=ZjljEpPMeRBse75NgUiwbh01KuM&redir_esc=y#v=onepage&q=Co2%20sensors%20and%20health&f=false
   3. https://ieeexplore.ieee.org/abstract/document/8767280

4. Is it possible to obtain MEMS separately from the module along with the compensation software to integrate them into a custom DSP solution?
   No, currently it is not possible to purchase MEMS separately.
   
   
5. How is the sensor calibrated? Does it need recalibration after delivery?
   Each sensor is calibrated in the factory when it is shipped from Infineon. For the final product, you  will not have to perform calibration. However, you should use the automatic baseline offset correction (ABOC) feature during operation to minimize errors due to aging. See the application note, FCS_ABOC_XENSIV™ PASCO2.
   
   
6. How can I generate a known level of CO₂ in ppm?
   CO₂ sources are numerous such as bike tire CO₂ inflators, soda water, and human breath. To arrive at a known level, capture the CO₂ gas in a Tedlar bag and pump it into a gas chamber using a 6-V diaphragm pump. CO₂ concentration can easily reach more than 10000 ppm in such a setup. A reference CO₂ sensor can be used to measure the known level. See the application note, Recommended performance evaluation methodology for XENSIV™ PAS CO2 sensor.
   
   

   One such setup is as follows:
   

7. Can the XENSIV^TM PAS CO₂ sensors be battery-powered?
   XENSIV^TM PAS CO₂ can be used for battery-powered applications. Infineon has a reference design which can help operate the sensor at 3.3 V (a low-cost boost converter circuitry along with the sensor). For details, see the application note,

   XENSIV™ PAS CO2 for low-power application.

8. When is the CO₂ sensor available? Where can I get eval kits?
   

    

   Evaluation kits are already available with major distributors.

9. What are the power requirements of the XENSIV^TM PAS CO₂ sensor?
   The average power consumption to power up the sensor is 29.7 mW. During the measurement phase, the power consumption is 26.4 mW. Infineon provides a power calculator based on Microsoft Excel that helps in determining the average power consumption based on the end application.
   

   Figure 4. Average power consumption

   For more information, see Section 3 of the application note, XENSIV™ PAS CO2 for low-power applications.

10. What is the long-term stability of these sensors?
    

     With the automatic baseline offset correction (ABOC) feature enabled, the sensor accuracy drifts by 1% every year.

    

    Figure 5. Values of pressure and acoustic stability

    See Section 4.1.5 - Transfer function table in the datasheet.

11. How can I reduce a high CO₂ level?
    According to ASHRAE, an ideal living room should not have more than 1100 ppm of CO₂. Therefore, as soon as the CO₂ level increases beyond 1100 ppm, you should ventilate the room.
    
    
12. How is the sensor calibration done?
    
    • Does the sensor calibrate single gas or more gases?
    • How long does the calibration process take?
    • What is the required equipment?
    • How often calibration must be done?
    • Can the calibration be done anywhere or only in the laboratory?
    • Does the sensor have automatic calibration or auto leveling?

Each sensor is calibrated during our production for the complete operating range. Production calibration is done with highly accurate CO₂ gas bottle and verified with an ideal reference sensor.

The sensor might show small amount of offset after assembly due to stress generated from the assembly process on the light source. Therefore, to get the best performance, this offset should be corrected using either FCS or ABOC.

For the FCS calibration, you need to have a reference sensor. In the ABOC mechanism, the device keeps track of the minimum value recorded over a week. The offset to the reference baseline is computed and used to calculate the correction factor to be applied for the week after.

Figure 6. Operation of the ABOC feature

See the application note, After-assembly calibration scheme for XENSIV™ PAS CO2 for more details.

13. Can this device be installed on a microcontroller/system-on-chip such as Arduino/Raspberry Pi?
    Yes. Infineon provides C/C++ libraries for interfacing the sensor.
    See the following GitHub repos:
    
    • For devices compatible with Arduino.
    • For PSoC™ 6 MCU library.

14. Does the response time (T63 = 75s) meet the certification requirements and accuracy for medical applications?
    The sensor is not specifically designed to cover medical applications. However, the response time is defined based on the diffusion process.
15. What are the design rules for integrating the CO₂ sensor into a package for airflow speed and direction?The device must be positioned in such a way that the diffusion of CO₂ molecules can happen easily, with a large enough opening. The recommended opening is at least 14 mm x 14 mm.
    

     

    Figure 7. Airflow direction

 See the application note, General design in guidelines for XENSIV™ PAS CO2 sensor for details.

16. What is the time constant (CO₂) of the sensor?
    Time constant/response time of the sensor is the time it takes to measure the CO₂ concentration. This is due to the diffusion time of CO₂ molecules.
    For VDD3.3 = 3.3 V, VDD12 = 12 V, Tamb = 25°C, % RH = 30 %, p = 1013 hPa, the response time, T63 = 75 seconds.
    See Section 4.1.5 of the datasheet for more information.
    
    
17. What are the response times in different airflows?
    The response time is independent of the airflow. You should not place the sensor directly within the airflow. For more details, see the application note, General design in guidelines for XENSIV™ PAS CO2 sensor.
    
    
18. How do I waterproof the sensor board for wet environments?
    The sensor is not designed for applications where it must be waterproofed. The sensor may be damaged if submerged in water.
    
    
19. Is the CO₂ sensor tested in an environmental chamber?
    A test chamber is used, which  ensures that there is no leakage, and it can maintain laminar flow while exposing the sensor to the target gas concentration. Inside the test chamber, you should accommodate a reference CO2 sensor. Additionally, to get an overview of the complete test conditions, the pressure sensor, humidity sensor, and temperature sensor should also be considered.
    For more information, see the application note, Recommended performance evaluation methodology for XENSIV™ PAS CO2 sensor.
    
    
20. Can the sensor be used within battery-driven consumer goods, with a supply voltage lower than 12V, such as 3.3 V?
    Infineon has addressed the requirement; a reference design is available to ease the design process. You can use this design to realize 12V with relatively low effort. For more information, see the application note, Reference design Sensor2Go kit, and the detailed knowledge base article (KBA).
    
    
21. What are the major technologies used in the sensor?
    The sensor uses a microphone, emitter (MEMS + filter), and the embedded software that implements the sensing algorithm

Note: For more information, see the Community webpage for CO2 sensor where you can find answers to your questions and ask your own.