This page aims to answer all your important questions about gas measurement and sensor technologies as well as the maintenance and operation of our devices. You will also find definitions of relevant gas detection terms in our glossary.

General information and questions about GfG products

We offer a wide variety of both portable gas detection devices and fixed gas detection systems. The best way of finding the most suitable model for your application is a personal consultation with one of our experts. 

We strongly recommend carrying out a daily visual inspection (for mechanical damage and contamination) and a bump test to increase occupational safety when handling our portable gas detectors. You will also have to perform function checks and sensor adjustments on a regular basis. Please adhere to the applicable national regulations and requirements of your industry as well as the operating manual. For maintenance and repair work, please contact GfG or your sales partner.

The devices have different sensor equipment and ATEX approvals:

  • G999C: 1 catalytic combustion sensor, 3 electrochemical sensors, 1 infrared sensor (Ex zone 1).
  • G999M: same sensor equipment as G999C, but suitable for use in Ex zone 0
  • G999E: 4 electrochemical sensors, 1 infrared sensor (Ex zone 0)
  • G999P: 1 photoionization detector, 3 electrochemical sensors, 1 infrared sensor (Ex zone 0)

The configurations "C" and "M" also apply to the G888 series.

This question cannot be answered simply by stating an area in square meters, since the effective range depends on a variety of factors. The type of gas, possible leakage points and the manner of ventilation all influence the necessary number of transmitters and their recommended installation locations. We highly recommend contacting us in advance - our experienced experts will certainly find the right solution for your individual needs.

That depends heavily on the device and sensors you are intending to use and the gases you need to measure. GfG's portable gas detectors have slots for a maximum of five different sensors, giving them the ability to measure up to eight gases simultaneously, depending on their sensor configuration. The transmitters used in fixed gas detection systems usually have only one sensor and can therefore only measure a single gas. We will be happy to assist you in finding the best solution for your individual needs in a consultation meeting.

There is no clear answer to that, as the service life is influenced by the average daily usage time of the devices, their charging cycles, the number of alarms that have been triggered etc. However, the service life of a rechargeable battery is limited. At some point, their ability to store energy will gradually decline. You will notice this is the case when a device's charging time increases, while its operating time decreases. Please call our service staff if this happens, so they can replace the battery. 

The sensors, like the batteries, only have a limited service life. The approximation we can give is only a guideline and will be affected by factors like ambient conditions (mainly temperature and humidity) and their exposure to gases. Sensors will therefore sometimes have to be replaced before the expected end of their service life. The measuring principle also influences their service life. Infrared sensors, for example, will usually last longer than electrochemical sensors. For more detailed information, please refer to your product's user manual. 

This is usually due to the cross-sensitivity of the sensor. This means that a sensor does not respond exclusively to the target gas, but also to other influencing variables. In other words, a sensor with cross-sensitivity does not have perfect selectivity. This is particularly challenging for gas sensors, because the measurement of a specific gas should ideally be possible in a gas matrix of any complexity - with hundreds of gases and vapors potentially interfering. However, perhaps unsurprisingly, almost all measuring principles used in gas sensors exhibit some degree of cross-sensitivity to at least one other gas. 
In addition to cross-sensitivity, however, humidity or temperature can also falsify the displayed result.

What is special about the EC22 O is not based in chemistry at all, but rather in the way oxygen diffuses into the sensor.

Usually, gas detection devices use oxygen sensors with a limited diffusion current. With this technology however, oxygen diffuses through a capillary tube to reach the sensor. The sensor signal is then determined primarily by the physical laws of diffusion speed of gases in capillary tubes. Consequently, these devices measure the percentage of oxygen, while the ambient pressure dependence is relatively low. The measured value also depends on the relative molecular mass of the displacement gas. Devices like these are designed for detecting oxygen displacement caused by nitrogen. However, if air is displaced by e.g. helium, the measured value will be significantly higher than the actual oxygen concentration which can have dire consequences.

On EC22 O sensors, the gas diffuses through a membrane instead. The diffusion – and thus also the sensor signal – is linearly proportional to the partial pressure of oxygen in the ambient air. Changes in atmospheric pressure also affect the oxygen partial pressure linearly, which partial pressure sensors will detect accordingly. The relative molecular mass dependency described above does not occur in this process. This means, correct measured values will still be displayed even if oxygen is displaced by helium. In many applications, measuring the oxygen partial pressure makes more physiological sense than measuring the relative oxygen content in the atmosphere.


Adjustments of the zero point and the sensitivity of the gas detector / sensor with a known zero gas or test gas.

Threshold value of a specific gas concentration at which a display, alarm or other output signal is triggered by the device. The alarms and the measures initiated when an alarm is triggered must be set individually for each application as part of its risk assessment.

All GfG devices with catalytic sensors for combustible gases and vapors (CC) have an integrated protective function. If the measuring range is exceeded by 12 percent (112 % LEL), the sensor is disabled for safety reasons. One reason for that is the risk of explosion. The other is that the measuring signal would decrease again with increasing gas concentration, as there would be no oxygen available at the sensor, which is required for catalytic combustion.
The ambiguity would occur at the point where, while the gas signal was falling, one could no longer differentiate between a decrease in the actual gas concentration or an increase in the gas concentration in the absence of oxygen.
Disabling the CC sensor also prevents excessive wear at such high concentrations of combustible gases. Only when it has been ensured that no more combustible gas is present at the device may this condition be eliminated with an acknowledgement by the user. During this time, the device will clearly indicate the measurement range being exceeded. 

Comparison of the values displayed on a gas detector / sensor with a known test gas concentration without adjusting. Depending on the degree of deviation detected

  • the device can continue to operate within the permissible deviation from the set value
  • the device must be adjusted
  • the device must be repaired

A gas that causes the sensor to react even if the sample gas is not present or falsifies the measurement result when sample gas is present.

In general, the cross-sensitivity of a measuring device describes its sensitivity to variables other than the measured one. In gas detection, the cross-sensitivity describes how strongly and to which other gases a sensor reacts. The lower the cross-sensitivity, the more accurate the expected measurement results for the monitored gas will be. 

These abbreviations denote explosive (EX), toxic (TOX) gases and oxygen (OX).

Explosion-proof in this case means that devices may be used and operated in potentially explosive atmospheres. Many GfG devices are ATEX certified, which means they meet the necessary safety requirements and cannot trigger the ignition of hazardous air-gas mixtures in potentially explosive atmospheres.

The International Protection class (IP; also Ingress Protection) indicates how securely the equipment is protected against the ingress of solid foreign bodies and water. It is specified as "IP" followed by two digits. The first digit (0-6) indicates the degree of protection against solid bodies and the second digit (0-9) the degree of protection against the ingress of water. The higher the digits, the higher the protection.

In the field of explosion protection, "type of protection" designates different device construction principles. It is intended to minimize the risk of the simultaneous presence of an explosive atmosphere and ignition sources. The type of protection "i" (for intrinsic safety) describes the technical property of a device that prevents unsafe conditions, even if an error occurs. The current strength and voltage are limited to values that do not permit ignition of explosive air-gas mixtures either by sparks or by heating.

The flammable gases and vapors in air will only generate explosive mixtures within a certain concentration range. Below and above these lower and upper explosion limits, the gas-air mixtures are not explosive. Up to the lower explosion limit (LEL), the gas-air mixture is too lean for combustion. Above the upper explosion limit (UEL), the oxygen required for combustion is not present in sufficient quantities.

  • Threshold limit value - time-weighted average (TLV-TWA): average exposure on the basis of an 8h/day, 40h/week work schedule
  • Threshold limit value − short-term exposure limit (TLV-STEL): a 15-minute TWA exposure that should not be exceeded at any time during a workday, even if the 8-hour TWA is within the TLV-TWA.
  • Threshold limit value − ceiling limit (TLV-C): absolute exposure limit that should not be exceeded at any time

Gas/air mixture used as a substitute for any test gases that would be too difficult to handle on a regular basis.

The response time t100 is the period of time that a measuring device needs to react to an abrupt change in the value of the measurand with a corresponding change in the measuring signal. The change in the measurement signal itself is not erratic, but runs in the form of a logarithmic curve, that is one that becomes increasingly flat with time. The shorter the adjustment time, the faster you will receive the effective concentration of a gas from your transmitter, for example.

The accuracy adjustment of the last 10% takes a disproportionately long time, both when rising and when falling. Intermediate values such as t90, t50 or, in the case of falling gas concentration, t₁₀ are much more important in practice. They will provide far better response times with sufficient accuracy. 

The gas or gas mixture you need to monitor. It usually consists of air, the target gas and other components.

The gas or gaseous substance you want to detect.

Gas mixture of known composition used for the calibration and adjustment of gas detection devices.

The time required until the device can be operated after it has been switched on.

Test gas that contains neither the target gas nor interfering impurities.

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