Air Monitor Calibration: A Step-By-Step Guide For Accuracy

Calibration is essential to ensure the accuracy of air quality monitors. While the specific calibration process depends on the type of monitor, the underlying principle is the same: aligning the monitor's readings with standardised values. For instance, gas detectors rely on sensors that measure specific gases in the air, but these sensors are not fail-safe, so regular calibration is necessary to ensure accurate readings. Calibration methods range from manual processes outlined in the owner's manual to automatic re-calibration using docking stations. Some monitors, such as smart indoor air quality monitors, can be calibrated through their corresponding applications. It is worth noting that calibration tools and software are also available for computer monitors, allowing users to optimise display colour for their specific screens and lighting conditions.

Calibration tools and software

Calibration Tools

• Reference analysers: These are standard instruments used to calibrate air quality monitoring devices. They are typically used in controlled environments and may not be suitable for calibrating small sensor systems.
• Diffusion tubes or passive samplers: When access to a reference analyser is limited, diffusion tubes or passive samplers can be used as an alternative. They offer traceability to a certified standard, providing data quality assurance.
• Co-location: This method involves calibrating one unit against a reference analyser and then co-locating that unit with other sensors in a convenient location. It is important to maintain a close distance between the sensor and the reference inlet to ensure accurate calibration.
• Field normalisation: Field normalisation techniques are used to calibrate sensor responses against reference measurements. Linear regression is commonly employed, but more advanced methods such as multi-linear regressions and machine learning algorithms are also explored.

Calibration Software

• SafetyCulture Air Quality Monitoring Software: SafetyCulture offers a comprehensive platform for air quality management. It enables remote tracking and analysis of air quality parameters, automation of routine checks and equipment maintenance, and provides alerts for incidents like poor ventilation or exposure to air contaminants. The software is available on mobile apps (iOS and Android) and as a web-based application.
• Aeroqual Air Quality Monitoring Software: Aeroqual provides advanced sensor technology and a modular design, allowing companies to customise their monitoring system based on specific requirements. It offers remote monitoring, service events recording, and is compatible with web, iOS, and Android platforms.
• Kaiterra Air Quality Monitoring Software: Kaiterra specialises in indoor and outdoor air quality monitoring, providing hardware that reads particulate matter, carbon dioxide, temperature, and relative humidity. They cater to large enterprises, including Fortune 500 companies. The software is compatible with web, iOS, and Android platforms.
• Envizom by Oizom: Envizom offers three levels of analytics: parametric, location, and time-span comparisons, helping companies effectively reduce pollution rates and comply with regulations. It is a web-based platform.
• Envirosuite Air Quality Monitoring Software: Envirosuite is a global leader in environmental management solutions, providing high-quality software for comprehensive air quality monitoring. Their platform includes features such as 24/7 ambient air quality monitoring, operational scenarios with impact prediction, and incident investigation. It is a web-based solution.
• ERA Environmental Air Quality Monitoring Software: ERA Environmental is a top-rated environmental software provider, offering advanced emissions tracking capabilities and customisable reporting functionalities. Their platform enables companies to collect, analyse, and report on air quality data while maintaining compliance with government regulations. It is available on web, on-premise, iOS, and Android platforms, with pricing starting at $125/month.
• ENVEA Air Quality Monitoring Software: ENVEA provides digital solutions, hardware, and services for industrial facilities, government agencies, and research institutions. Their platform includes data acquisition, processing, and display capabilities, automatic comparisons with regulatory pollutant limits, and advanced statistics and reporting. It is compatible with web, iOS, and Android platforms.

Manual vs automatic re-calibration

Manual calibration of an air quality monitor involves zeroing the meter to reset its reference point. This may require "zero air" gas. It is important to ensure that the test gas is not expired and that its concentration is high enough to trigger the instrument's alarm. The gas is then applied to the monitor, and the instrument's readings are checked. These readings should fall within an acceptable range, typically ±10-20% of the test gas concentration. If the monitor does not recalibrate or the alarm is not triggered, one may try recalibrating the monitor with a new test gas or contacting the manufacturer for assistance.

Automatic calibration, on the other hand, requires a docking station for the monitors, which also charges them. This process tends to save time and reduce the chance of errors. The system will alert users if the monitor fails to recalibrate properly. Docking stations will also update calibration records on the included software automatically.

While manual calibration provides more control over the process and allows for adjustments specific to the user's needs, automatic calibration is more convenient and reduces the risk of errors. It is also important to note that some monitors, such as the Airthings View Plus, do not offer manual recalibration. In such cases, automatic calibration is the only option.

It is worth noting that, regardless of the calibration method, the responsiveness of monitor sensors can vary due to factors such as temperature, humidity, and atmospheric pressure. Therefore, it is crucial to calibrate the sensors in environmental conditions as close to the worksite conditions as possible. Additionally, calibration drift can occur over time, causing the instrument's reference points to shift and resulting in unreliable readings. Regular calibration, therefore, helps to verify and update the instrument's reference point.

In conclusion, both manual and automatic re-calibration methods have their advantages and disadvantages. The choice between the two depends on factors such as the user's preference for control versus convenience, the availability of manual calibration options, and the specific requirements of the monitoring equipment and its sensors.

Calibration gases

The calibration gas in the cylinders has an expiry date, as the gas quantity (concentrations) in the container may change over time. Therefore, it is crucial to store the calibration gas according to the manufacturer's recommendations to maintain stability. Using expired gas may lead to inaccurate calibration results.

Calibration gas is also used for "bump testing", a quick check to ensure the device responds to a gas concentration. Bump tests are recommended before every use of the gas monitor, whereas full calibration is usually done less frequently, depending on the manufacturer's guidelines and the frequency of equipment usage.

Calibration frequency

For air quality monitors, it is recommended to calibrate them once a month. This is because accuracy can drift over time due to panel degradation. However, if the monitor is not used regularly, it may not need to be calibrated as frequently.

According to the Occupational Safety and Health Administration (OSHA), it is ideal to calibrate gas detectors before each use to ensure accurate results. However, this may not be practical for many teams. In such cases, it is recommended to follow the manufacturer's guidelines for calibration frequency. Additionally, the International Safety Equipment Association (ISEA) recommends verifying the operational capability of gas monitors before each day's use.

Automated Calibration Systems

If you use gas monitors regularly or have a large number of monitors to calibrate, an automated calibration system can be used. This system will automatically calibrate the monitors overnight or when they are not in use. This way, they are ready for use the next day.

Bump Tests

A bump test or function check is a qualitative check to ensure that gas can reach the sensor(s) and that all alarms are functional. This test does not provide a measure of the instrument's accuracy. It is recommended to perform a bump test before each use of a gas monitor. If the initial bump test fails, a full calibration is required.

Calibration for different media

Calibrating Air Quality Monitors

Air quality monitors require regular calibration to ensure the accuracy of their measurements. This can be achieved through hardware calibration, software calibration, and laboratory calibration:

• Hardware Calibration: This involves calibrating the sensors with standard gases and regularly checking the mechanical parts, circuitry, and power supply.
• Software Calibration: This focuses on calibrating the data processing and analysis capabilities, including the data processing algorithms and calculation methods of the air quality index.
• Laboratory Calibration: This involves placing the air quality detector in a standardised environment and comparing its measurements with other high-precision instruments to verify accuracy.

Calibrating Computer Monitors

Computer monitors can be calibrated to improve image quality and colour accuracy. While basic built-in calibration tools are available in Windows and MacOS, more advanced calibration can be achieved through specialised software and hardware tools:

• Resolution and Scaling: Ensure that the display resolution matches the native resolution of your monitor. Adjust the scaling settings to your preference to strike a balance between readability and multitasking capabilities.
• Brightness: Reduce the brightness to a comfortable level that preserves detail in dark images. Aim for a brightness of around 200-300 lux.
• Contrast: Adjust the contrast to ensure all bars on a contrast test image (such as the Lagom LCD contrast test image) are visible without bleeding colours.
• Sharpness: Adjust the sharpness setting to your preference, as it is highly subjective and not part of standard colour profiles.
• Gamma: Use a test image (such as the Lagom LCD gamma test image) to adjust your monitor's gamma settings to a value of around 2.2, which is commonly accepted as a solid option for computer monitors.
• Colour Temperature and White Point: Aim for a colour temperature of 6500K, which is the standard for most screen calibrations and is equivalent to midday light. However, you can also adjust this based on your personal preference.
• Colour Gamut: Switch to an sRGB mode for standard colour gamuts or DCI-P3 mode for wide colour gamuts. Keep in mind that these modes may lock your monitor's brightness and gamma controls.

Calibrating Audio Devices

Audio devices, such as speakers and headphones, can also be calibrated to optimise sound quality and ensure accurate audio reproduction. This can include adjusting settings such as volume, bass, treble, and equaliser (EQ) settings. Additionally, audio interfaces and digital audio workstations (DAWs) may require calibration to ensure accurate audio recordings and mixing. This can involve the use of calibration software and hardware, such as audio analysers and room correction tools.

Calibrating Other Devices

Other types of media and devices that may require calibration include cameras, printers, and scientific instruments. Each type of device will have its own specific calibration procedures and settings. It is important to refer to the manufacturer's instructions or seek specialised advice for calibrating these devices accurately.

Frequently asked questions