What is Zero Calibration?
Why Do NDIR Sensors Need Zero Calibration?
NDIR sensors detect gases like carbon dioxide (CO₂) by shining infrared light through the air and measuring how much light is absorbed. Less light equals more gas. But, over time, things like dust and temperature changes can cause the sensor to drift. This means the sensor can display a small reading even when there is no gas around. The sensor is not damaged or broken - it can still “see” as well as it always could. It just needs to be recalibrated to its zero point.
How is This Done?
The gas sensor is exposed to a special gas that doesn’t contain any of the target gas it’s meant to detect. The sensor takes a reading, then is adjusted so that this measurement becomes the new "zero"
point. The sensor must already have been running for a certain amount of time to ensure accurate zero calibration.
What is a "Clean Air" Calibration?
Sometimes it might not be practical or possible to zero calibrate a sensor using zero gas. A less accura-te version of zero calibration exists, known as “clean air” calibration. This works by telling the sensor that the air around it has none (or a very low, known amount) of the gas it is trying to measure. When performing a clean air calibration on CO₂, for example, it is important to be careful. Even having a window open or closed in a room can affect readings, as can changes in the temperature or air pressure, or being around cars or people. The sensor must stay in this clean air spot and have time to warm up and stabilize, which usually takes between 10 and 60 minutes. It is also best practice to make sure the temperature and humidity are steady and within the range of what the sensor can handle.
How to Carry Out Zero Calibration on Micro-Hybrid Devices?
The method varies depending on the specific sensor, but let’s consider the Micro-Hybrid MicroSENS 180-HS NDIR gas sensor for CO2 measurement in incubators.
To initiate zero calibration:
- Use the command code “1203”.
Append the known concentration of CO₂ in the environment (in hundredths of a percent by volume). For instance, if the measured CO₂ is 0.04% Vol.-%, add “40” to the code.
The complete command format is:
STX 120340 ETX
- STX: Start of transmission
- 1203: Command to initiate zero calibration
- 40: CO₂ concentration as 0.04%
- ETX: End of transmission
Again, this is only an example. Always consult your device’s documentation to confirm the correct command format and calibration procedure for your specific model.
How Often Should You Do This?
There is no universal answer for how often to perform zero calibration on a gas sensor, as it largely depends on your accuracy requirements. While calibrating too frequently won't harm the sensor, it's not necessary. Once a month is a typical recommendation for many applications, but there is no one solution that is ideal for all use cases. For guidance tailored to your specific Micro-Hybrid product and application needs, please feel free to contact us. We will be happy to help you leverage our expertise.
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