CO₂ Incubator Sensor Calibration Facts

Every MicroSENS 180-HS CO₂ sensor leaves Micro-Hybrid’s factory with a 15-point calibration - five gas concentrations tested at three different temperatures. Each calibration uses DAkkS-traceable reference gas to guarantee accuracy and repeatability. This multi-point approach delivers exceptional linearity across the full 0 - 20% measurement range, far exceeding the precision of many sensors that undergo only a simple 3-point calibration.

But even with such a robust foundation, every NDIR sensor benefits from periodic recalibration to maintain peak performance in real-world conditions. In this guide, we’ll take a practical look at when and how to calibrate your MicroSENS 180-HS sensor to ensure reliable CO₂ readings over its lifetime.

To begin with, if you’re integrating the sensor into an incubator, we recommend starting with a zero-point (clean air) calibration during installation, followed by a span gas calibration and, if needed, a quick reverification after sterilization.

For end customers using this sensor, we recommend a clear air calibration after every 12 sterilization cycles. One of the key advantages of this sensor is its high resistance to drift, even after numerous sterilization cycles. Nevertheless, it is recommended the end user calibrate after every 12 cycles for optimum upkeep. Clean-air calibration should also be carried out (regardless of how many sterilization cycles have occurred) if it becomes apparent that the sensor is experiencing a loss of accuracy due to drift. We do not recommend calibrating this sensor by using a third-party sensor as a baseline: many competing sensors do not compensate for atmospheric pressure automatically, like Micro-Hybrid sensors do, and thus we recommend they be considered not accurate enough to be used as a trusted baseline.

Lat us further discuss the three types of calibration are possible for this sensor.  

Before performing a zero-point calibration, verify that all of the following conditions are met:

• Stable environment: perform the calibration in a well-ventilated area with clean, uncontaminated air. Avoid locations near CO₂ sources such as people, open incubators, exhaust outlets, or gas lines.
• Reference concentration: the reference gas for zero-point calibration should be 4.0 (99.99%) pure nitrogen gas, or purer.
• Temperature equilibrium: the gas temperature should be approximately equal to the sensor body temperature to prevent drift caused by temperature gradients. We recommend you let the reference gas container sit in the same room as the gas sensor for an hour before the gas is used.
• Gas flow: if using a gas supply, the flow rate must not exceed 1 l/min.
• Atmospheric stability: perform calibration under stable pressure conditions; avoid drafts or rapid environmental changes.

Follow the following procedure:

• Power on the sensor and allow it to stabilize for at least 15 minutes.
• Verify that the CO₂ reading is stable.
• Use a calibration cap to cover the sensor head as you supply the gas through the tube, or, if calibration is being carried out in the incubator, flush the gas to the incubator. (A calibration cap is available for purchase from Micro-Hybrid upon request.)
• Do this until the CO₂  levels are stable. When a cap is used, this will take approximately one minute; when the gas is flushed to the incubator, approximately 15 minutes.
• Send the Zero-Point Calibration Command (“STX120340ETX”) via the digital interface.
• Wait for the sensor to return a confirmation message (STX 0 ETX) indicating successful calibration.
• If calibration fails (STX 1 ETX), repeat the procedure after confirming gas purity, temperature stability, and flow conditions.
• Once calibration is successful, record the calibration date, reference gas, and ambient conditions for quality and traceability.

Before performing a clean-air calibration, verify that all of the following conditions are met:

• Stable environment: perform the calibration in a well-ventilated area with clean, uncontaminated air. Avoid locations near CO₂ sources such as people, open incubators, exhaust outlets, or gas lines.
• Atmospheric stability: perform calibration under stable pressure conditions; avoid drafts or rapid environmental changes.

Follow the following procedure:

• Power on the sensor and allow it to stabilize for at least 15 minutes.
• Verify that the CO₂ reading is stable.
• Send the Zero-Point Calibration Command (STX120360ETX) with a reference value of 0.06 Vol.-% CO₂ (equivalent to 600 ppm). (The 0.06 Vol.-% mentioned here is a general recommended figure. In real world conditions, different rooms will typically have a typical CO₂ measurement of between 0.04 and 0.08 Vol.-%. The operator of this sensor is free to adjust this figure as best suits their particular use case.)
• Verify the response (STX 0 ETX) indicating successful calibration.
• Record the calibration result, environmental conditions, and date for documentation.

Before performing a span gas calibration, verify that all of the following conditions are met:

• Use test gas with a dry and clean CO₂ concentration between 0.500 and 20 Vol.-%.
• Ensure that the sensor has reached thermal stability before starting the span calibration.
• Temperature equilibrium: the gas temperature should be approximately equal to the sensor body temperature to prevent drift caused by temperature gradients. We recommend you let the reference gas container sit in the same room as the gas sensor for an hour before the gas is used.
• Gas flow: if using a gas supply, the flow rate must not exceed 1 l/min.
• Atmospheric stability: perform calibration under stable pressure conditions; avoid drafts or rapid environmental changes.

Follow the following procedure:

• Power on the sensor and allow it to stabilize for at least 15 minutes.
• Verify that the CO₂ reading is stable.
• Introduce the span gas and allow the reading to stabilize.
• The command you send to initiate a span calibration will include the Vol.% of the span gas you are using. For example, send Command STX14055000ETX if you are using a span gas of 5.0 Vol.%. For a span gas with a 20 Vol.% concentration, enter the command  STX1405200000ETX
• Wait for the confirmation message (STX 0 ETX) indicating successful calibration.
• Verify the response (STX 0 ETX) indicating successful calibration.
• If calibration fails (STX 1 ETX), repeat the procedure after confirming gas purity, temperature stability, and flow conditions.
• Calibration parameters are stored permanently in the sensor’s internal memory, unless a factory reset is performed.

Calibrating your MicroSENS 180-HS doesn’t need to be complicated. With a solid understanding of when and how to perform zero-point and span gas calibrations, you can easily maintain the precision the sensor is designed to deliver.