Calibrating gas detectors is essential to ensure reliable measurements and, most importantly, to protect people and processes. When sensors are properly adjusted, the equipment identifies dangerous concentrations with high accuracy. This prevents failures from becoming serious safety risks.
What happens during gas detector calibration?
During calibration, the technician exposes the detector to a known, pre-certified concentration of gas. Based on this exposure, the technician adjusts the sensors to reflect actual risk levels. Unlike bump test, which only confirms the response of the sensor and alarms, calibration corrects possible deviations and maintains the accuracy of the equipment.
How is standard gas used?
Calibration can only be performed reliably when using a standard gas. Typically supplied by the manufacturer, this gas is stored in cylinders and labeled with the exact concentration. This value serves as a reference for adjustment. Therefore, using certified gases is essential to ensure technically valid results.
Why calibrate frequently?
Over time, factors such as dust, humidity, temperature fluctuations, and even natural sensor wear and tear compromise measurement accuracy. This is why periodic calibration is so important. Besides preserving the detector's performance, it prevents unexpected failures and reduces operational risks. In other words, it's an essential preventative measure for safety.
What is the recommended frequency?
The ideal frequency depends on the type of application, environmental conditions, and manufacturer's instructions. While there is no single interval, the standard NBR IEC 60079-29-2 recommends following the instructions in the equipment manual. In areas with high temperatures, intense humidity, or the presence of contaminants, it's best to shorten the calibration period. At Alutal, for example, the recommendation is to perform calibration every six months.
Where to perform calibration?
Calibration can take place in different locations, as long as suitable conditions exist:
- Accredited laboratories (ISO / IEC 17025): Ideal for those who need maximum precision and traceability in results.
- In the field (installation location): A good option when there's local infrastructure. The detector remains installed, which speeds up the process.
- Specialized technical centers: Recommended in cases where the plant environment does not offer stability for reliable adjustments.
Who should perform the calibration?
Calibration requires technical expertise and must be performed by trained professionals. Furthermore, it's important to follow specific standards and manufacturer guidelines. Whenever possible, relying on accredited companies or laboratories increases safety and ensures the reliability of the data obtained.
What are the steps in the process?
Calibration follows two main phases:
- Zero Calibration: At this stage, the technician exposes the detector to clean air or nitrogen. The goal is to properly zero the sensors and eliminate residual readings.
- Span Calibration: The reference gas is then applied to adjust the sensor response to a known concentration.
Both steps require strict flow control and the exclusive use of certified gases. This ensures that readings are stable and within the standards required by regulations.
What gases are used?
The choice of gas depends on the sensor and the application. Here are the most common:
- Catalytic sensors (pelistor): They require oxygen to function, so they use mixtures of clean air (20,9% O₂).
- Infrared (IR) sensors: They use nitrogen (N₂) for both zero calibration and concentration adjustment, depending on the mixture.
- Most commonly used gases: Methane, carbon monoxide, carbon dioxide and hydrogen sulfide.
How important is calibration for safety?
Keeping detectors calibrated ensures not only technical performance but also the protection of people, assets, and processes. When calibration is performed correctly, the detection system responds accurately and contributes to safer operations. Furthermore, the risk of unexpected failures is significantly reduced, promoting confidence in daily operations. This reduces the risk of failures and interruptions, promoting greater safety and reliability.
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Bibliography
- International Safety Equipment Association – ISEA
- ABNT NBR IEC 60079-29-2:2024 – Explosive atmospheres Part 29-2: Gas detectors – Selection, installation, use and maintenance of detectors for flammable gases and oxygen
- ABNT NBR 16577 – Confined Space – Accident Prevention, Procedures and Protective Measures – 2017
