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Maintenance and Calibration of Gas Detectors

Gas detectors are an important safety feature in homes, industries, as well as workplaces and garages. In some places, the law mandates the use of detectors, while in others, it is a voluntary decision by the property owner or operator to help protect lives, health, and property. Detectors differ mainly based on the type of gas they detect and the environment they are designed for. Regular maintenance and calibration are always essential for their proper functioning.

Introduction: Glossary of Terms  

In the introduction of the article, we will present some key terms that will help you navigate the issue of calibration of gas detectors not only for households.

  • Calibration is the initial setting of the sensor range, which is performed during manufacturing, and its output is a calibration protocol. Simply put, calibration determines the signal threshold of gas concentration at which the detector's alarm is triggered.
  • Recalibration is the repeated comparison of measured values against a standard.
  • The standard is considered to be calibration gas, which is designated for this purpose. It is usually a calibration gas with a certificate of concentration accuracy. Using the calibration gas, a reference gas concentration value is stored in the detector's memory.
  • Sensor is the actual sensing element that converts the chemical concentration of the measured gas into an electrical signal.

Why and How Often Should Detectors Be Calibrated?

Given that sensors work with chemical and physical changes in materials, it is logical that they are subject to aging and lose their ability to respond to gas. This is precisely the reason for recalibrations. Over time, each sensor shows slightly differently, so it is necessary to adjust the measured values.  

So how often is it necessary to recalibrate detectors to ensure they function correctly? Gas detector calibration is mandatory every year according to Act No. 246/2001, which sets conditions for fire safety and the performance of state fire supervision (fire prevention decree). The specific interval for recalibrations is further adjusted by the installation and operating manual and the operating regulations issued by the safety technician in the given application.

The adjustment of the minimum recalibration interval in the manual is determined based on the sensor used. For common electrochemical and semiconductor sensors, it is usually 6-12 months. For more durable types of sensors, such as optical NDIR sensors, the minimum interval is longer, ranging from 1 to 5 years. The lifespan figure is thus only an approximate estimate based on experience. The actual lifespan is different for each piece and application. 

Industrial gas detectors EVIKON require regular maintenance and recalibration. 

What Affects the Lifespan of Sensors?

The lifespan of sensors is therefore very varied, depending on humidity, temperature, dustiness, frequency of exposure to the measured or interfering gas, and many other factors. Long-term exposure to the measured gas can even destroy some sensors. Similarly, exposure to gases with a concentration greater than the sensor's measuring range can be destructive. This often happens when using detectors near drains or during disinfection and cleaning.

Most sensors are also not selective and detect a range of gases. Even if a detector is calibrated, for example, to detect methane, an open can of paint near the detector can easily destroy it. Solvent vapors then penetrate the sensor, trigger a false alarm, and soon saturate and destroy it. 

Sensor aging can be slowed down by disconnecting from electrical power. A disconnected sensor ages significantly slower than a powered one. Thus, detectors can be stored for up to 6 months without recalibration and still perform the first recalibration 12 months after connection.

How to Recalibrate and Maintain Gas Detectors

As mentioned above, maintenance and recalibration of detectors are mandatory by law, and failure to comply with this obligation and the procedures set by the manufacturer results in the loss of not only the warranty but also the right to insurance compensation in the event of an insurance claim.

Maintenance of gas detectors varies according to their type and manufacturer. For example, small Honeywell home detectors are not calibrated but are discarded after their lifespan expires. For other types, it is necessary to:

  • perform regular recalibration,
  • replace the sensor after its lifespan expires,
  • conduct regular functional tests and checks of the protective dust filter.

The minimum intervals for these tasks are always determined by the manufacturer and must be followed. Service, functional tests, and calibration of gas detectors can only be performed by qualified individuals and service companies authorized by the manufacturer. The cost of recalibration varies depending on the type of detector, starting at approximately 600 CZK per piece and ending around 3,000 CZK per piece.

In addition to recalibrating detectors, do not forget about regular inspections of gas and gas appliances, the cost of which is negligible compared to the risk of an explosion.

Small Honeywell detectors for households are simply discarded after their lifespan expires. 

Recalibration of Gas Detectors

The method of recalibration varies according to the type of detector and manufacturer. Evikon detectors are calibrated annually and require calibration gas and calibration software. Recalibration of detectors from this manufacturer is carried out in two ways. The first is correspondence recalibration. The operator removes the detector and sends it for recalibration to the manufacturer or distributor. They power it for 48 hours and recalibrate it. After recalibration, they send it back to the operator. The second option is to contact one of the trained calibration partners. These are companies throughout the Czech Republic that are trained to perform recalibrations and have the necessary equipment.

Detectors from other manufacturers use their own software, and some manufacturers only adjust the potentiometer with a screwdriver. In any case, it is necessary for the detector to be connected to power for at least 24 hours before recalibration, but preferably 48 hours or more. This warming of the sensor is necessary to achieve measurement stability, which is required for its recalibration.

Sensor Replacement

Sensor replacement can only be performed by a trained person. Exceptions are semiconductor, optical, and photoionization sensors, which are replaced by the manufacturer because they require intervention in the detector's firmware. Electrochemical and catalytic sensors can be replaced simply by disconnecting the connector. After sensor replacement, it is necessary to calibrate the detector.

Functional Test

In addition to regular recalibrations and sensor replacements, functional tests are also conducted. The first is during the installation of the device, when after starting and stabilizing the measurement, test gas is released onto the sensor, and the detector's reaction is awaited. Further functional tests are prescribed by the safety technician through internal company regulations.

Checking the Protective Dust Filter

During functional tests and recalibration, the clogging of the protective dust filter, which protects the sensor, is also checked. Operating the detector without this filter reduces the sensor's lifespan and results in the loss of warranty. The filter is made of special multi-layer laboratory paper. It often happens that customers mistake it for a plastic cover and discard the filter.