- Functions and principle of operation
- Types of combined detectors
- What else is the reason for the difference in cost
- Verification and certification
- Installing the appliance
- Nuances of operation
Natural gas leakage is dangerous, and in order not to become the heroes of news stories, you should use protective devices – household sensors and gas leak alarms. There are a number of them for domestic use at home and in the country, and we will help you understand their variety, installation and use rules..
Functions and principle of operation
Household gas alarms are designed to determine the presence in the room atmosphere of a number of gases in concentrations that threaten human life and health. Unlike industrial and laboratory devices, gas sensors for civilian use have a smaller spectrum of substances to be determined, and also almost never have the functions of recording measurements and self-diagnostics. If you think about it, a limited number of compounds that can harm a person can be present in the room atmosphere: mainly natural gas, which is based on methane, as well as combustion products – monoatomic and diatomic carbon oxides.
One or more gas analyzers of different types of operation are installed inside each gas concentration sensor. Control over the leakage of combustible hydrocarbons is carried out primarily by monitoring the ability of the gas mixture to absorb infrared radiation. Thus, oxygen and hydrogen molecules are diathermic, while methane clearly exhibits the properties of a greenhouse gas. By tuning the device to a certain absorption wave, it is possible to quite accurately determine the type of substance to which the gas analyzer reacts..
Carbon dioxide is also capable of absorbing thermal radiation, although these properties are somewhat weaker. The problem is that a single infrared gas detector is not universal; a separate detector must be installed for each gas. In this case, carbon monoxide is absolutely diathermic, that is, it is not detected by infrared detectors. To detect it, thermochemical detection is used, the principle of which is put into the operation of catalysts for automobile exhaust systems. The bottom line is that when it gets on the catalyst, carbon monoxide is oxidized, causing the surface to heat up. When heated, the electrical resistance of the catalyst decreases, which is successfully recorded by the simplest electronic circuit.
Types of combined detectors
The device of gas leakage detectors is quite simple, which made it possible to reduce the price for an ordinary consumer to an acceptable one. The most expensive element inside a domestic leak detector is the gas analyzer, which requires a separate power circuit and individual calibration. Therefore, in their abilities, household appliances can be very different..
In the price range from 1 to 2 thousand rubles, the most simple devices of the combined principle of operation are located. The detectors of all three hazardous household gases are located inside one housing, and they are all connected to one alarm device. Sometimes such sensors do not allow us to determine what exactly caused the operation, which can definitely be attributed to the disadvantages of this group of devices.
More expensive devices (from 2 to 5 thousand rubles) not only have more advanced detection methods, but are also equipped with a number of important functions. For example, all devices of this class help to unambiguously determine which gas concentration is exceeded. It is also possible to have relay or analog outputs for connection to the boiler room automation unit. Such devices are able to automatically shut off the gas supply or turn on forced ventilation..
The most expensive gas contamination alarms are entire complexes consisting of stand-alone sensors of various types and a common control unit. Inside the latter there is a recorder, relay and analog outputs, a power supply. Such devices are used in rooms of complex shape and considerable length, where installation of several sensors is required..
What else is the reason for the difference in cost
The problem of choosing and operating household gas analyzers lies in their monoblock device. While all detectors are located at the same point, the concentration locations for all three gases are different. Carbon monoxide and methane are concentrated in the upper part of the room, while carbon dioxide is heavier than air under normal conditions. For domestic conditions, this is acceptable, because carbon dioxide is the least dangerous, but in certain situations this circumstance is categorically unacceptable. For example, a liquefied gas mixture from a cylinder is always heavier than air, which makes it necessary to install two sensors in the lower zone and under the ceiling of the room. Thus, devices with separate remote sensors are more profitable in such cases..
Carbon monoxide detectors can be found in complex alarm systems and smart home systems with support for GSM communication or via the Internet. In this case, the sensor readings can be checked even remotely using a phone.
Another nuance lies in the accuracy and reliability of the detectors. The general requirements set the threshold for methane concentrations of 10% of the ignition threshold (LEL) and carbon monoxide levels greater than 85 PPM (parts per million). The measurement error (no more than 10%) and the response time are also standardized. It should be said that all devices on the market fully comply with these requirements, but over time they may lose their properties. It is for this reason that gas contamination alarms require annual verification and there is a high risk that the device will simply not pass the next certification, which means that you will have to buy a new one..
Verification and certification
It is possible to establish whether the device meets the safety requirements by checking it on measuring simulators. This can be done at the nearest center for standardization, metrology and certification located in a government department. There are also private laboratories accredited to conduct this kind of activity, but they are engaged in testing industrial equipment, the price tag for services is also appropriate. You can get the address of the nearest test center at the Gorgaz, the cost of verification is from 300 to 500 rubles.
The verification of household gas alarms is also carried out before the device is put into operation: for unknown reasons, the manufacturer’s mark about the suitability of the device among gas workers is not quoted. However, in some gas services, signaling devices can be bought immediately with a certificate and a mark in the passport, although the price will be slightly higher. Do not forget that due to the need for regular verification, the passport of the device must be retained until its disposal..
Installing the appliance
There are no requirements for the method of fixing the gas alarm, it can be either screws or ordinary double-sided tape. Almost all devices are supplied in a plastic case, their weight is about 100 grams. The only thing to consider is the location in the immediate vicinity of an electrical outlet, because the length of the power cord of the device rarely exceeds 100-150 cm, while disassembling the device, using extension cords or extending the cord is not allowed.
The choice of the installation site is separately regulated. On average, the degree of protection of the signaling devices is not higher than IP 33, therefore, the device should not be installed in places where splashes, dust emissions, and exposure to steam and high temperatures are excluded. It also makes no sense to install gas signaling alarms in the immediate vicinity of the ventilation ducts of the windows..
The installation height of the devices is determined by its instruction-passport. On average, for combined detectors it is 0.5 m from the ceiling, for liquefied gas alarms – no closer than 0.5 m to the floor. If there are recesses in the floor, additional propane sensors should be installed in them..
After installation, the device must be checked for operability, but this must be done correctly. All you need is a balloon and a piece of wood. A small amount of gas must be drawn into the ball, for example from a stove burner. In this case, the gas should not be released directly into the intake grating of the detector, which inevitably leads to damage to the sensitive detector. Gas contamination is simulated by releasing small portions of gas from a distance of at least one meter. With a splinter, everything is easier: it is set on fire and extinguished, and the detector is fumigated with a stream of smoke at a distance of 20-30 cm.
Nuances of operation
In conclusion, we note that, despite the simplicity of the device, gas alarms are a very sensitive technique. To keep the device in good working order, it is necessary to protect it from pollution, accumulation of dust and cobwebs on the case..
Also, a characteristic feature of carbon monoxide analyzers is their long time to enter the mode, during which the device requires personal control. Some devices are designed to manually restore functionality after triggering. The procedure is described in the instructions and takes less than a minute.
The signaling device does not require maintenance, on the contrary: the case cannot be disassembled, otherwise the verification certificate will lose its validity. For this reason, the repair of the analyzers should be carried out in a specialized service center, despite the fact that any more or less experienced radio amateur can fix most of the faults..