We answer all important questions about gas measurement technology, technologies and the maintenance and handling of our devices. In addition, you will find some important definitions of terms related to gas measurement in our dictionary.

General information and questions about GfG products

We offer our customers portable gas detection devices and fixed gas detection systems in numerous versions. The best way to find out which device variant is most suitable for your application is an individual and personal consultation.

We strongly recommend that you carry out a daily visual inspection (for mechanical damage and contamination) and a display test. This increases occupational safety when handling our portable gas detectors. A regular function check and sensor adjustment must also be done. Please observe the country- or industry-specific requirements as well as the instructions in the operating manual. For maintenance and repair work, please contact GfG or your responsible 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)

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

This question cannot be answered simply by stating an area in square metres. It depends on a variety of factors: The type of gas, possible leakage points and the type of ventilation influence the number and the correct installation location of the transmitters. It is essential to take advantage of GfG's advice in advance.

This depends mainly on the device used, the built-in sensor and the gases to be measured. GfG's portable gas detectors have slots for a maximum of 5 different sensors. Depending on the sensor configuration, they can measure up to 8 gases simultaneously. The transmitters used in fixed gas warning systems usually have only one sensor and can therefore only measure a single gas. We will be happy to clarify which device is best suited for you in a consultation meeting.

No clear answer can be given to this question as a general rule, as the service life depends on the usage times of the device and the charging cycles. However, the service life of a rechargeable battery is limited. At some point, the ability to store energy is only partially available. This can be seen in the longer charging times and shortened usage times. In this case, a new battery must be inserted by GfG Service.

The sensors, like the batteries, only have a limited service life. This is a guideline value and can be negatively influenced by the room climate, mostly by temperature and humidity, or by exposure to gases. In this case, a sensor may also have to be replaced before the expeted end of its service life. Likewise, the type of measuring principle has an influence on its service life; for example, infrared sensors usually last longer than electrochemical sensors. You will find the exact information on this in the operating instructions of the respective product.

This is usually due to the cross-sensitivity of the sensor. This means that a sensor does not respond exclusively to the target measurand or target gas, but also to other influencing variables. In other words, a sensor with cross-sensitivity does not have perfect selectivity. This challenge is particularly great 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 vapours as potential interferers. It is therefore not surprising that almost all measuring principles used in gas sensors exhibit cross-sensitivity to a cross-gas.
In addition to cross-sensitivity, however, humidity or temperature can also falsify the displayed result.


Setting of the device to a specific gas concentration at which a display, alarm or other output signal is triggered by the device. The alarms and the measures to be taken when an alarm is triggered must be determined specifically for each application as part of its risk assessment.

Describes the time from switching on the gas detection device until it reaches readiness.

Within the field of explosion protection, there is the type of protection. This represents various design principles of equipment and is intended to minimize the risk of the simultaneous presence of an explosive atmosphere and ignition sources. Intrinsic safety "i" is the technical property of a device that ensures that no unsafe condition occurs even in the event of a fault. 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 t100 setting time is the time span 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, i.e. one that becomes increasingly flat with time. The shorter the adjustment time, the faster a transmitter, for example, displays the actual concentration of a gas.

Since it takes a disproportionately long time to settle to the last 10% accuracy 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. With sufficient accuracy, they deliver significantly better.

Gas/air mixture used as a substitute for a difficult-to-handle test gas.

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

Explosion-proof in this case means that devices may be used and operated in potentially explosive atmospheres. Many GfG devices have this so-called ATEX certification. They have the required safety 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. IP is indicated followed by 2 digits. The first digit (0-6) stands for the degree of protection against solid bodies and the second digit (0-9) for the degree of protection against the ingress of water. The higher the digits, the higher the protection.

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

Comparison of the display of 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 setpoint
  • the device must be adjusted
  • the device must be repaired
  • threshold limit value - time-weighted average (TLV-TWA): average exposure on the basis of a 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

The gas or gas mixture to be monitored. It usually consists of air, the target gas and other components.

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

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

In general, the cross-sensitivity of a measuring device describes its sensitivity to variables other than the measured variable. In gas measurement, 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 gas to be monitored.

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.

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 de-energized for safety reasons. On the one hand, there is a risk of explosion. On the other hand, the measuring signal would decrease again with increasing gas concentration, because the oxygen required for catalytic combustion would be missing from the sensor (ambiguity).
The ambiguity would occur at the point where, with the gas signal running down, it would no longer be possible to distinguish 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. Meanwhile, the device signals a clear overrange.

Flammable gases and vapours in air only form 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.

Gaseous substance which is detected in the measuring gas and of which a warning is to be given.

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