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1、 The practical application of optical radiation equipment in potentially explosive environments
Optical radiationThe issues of low visibility, multiple optical paths, and energy overlap in transmission have actually caused many safety hazards and even caused many accidents. Therefore, the safety research of optical radiation equipment and transmission systems has become a focus of its research. In explosive environments, optical equipment is mostly used together with electrical equipment. For example, lighting fixtures, lasers, light-emitting diodes used in communication, surveying, sensing, and measurement activities（LED）Optical equipment such as optical fibers. These devices are typically installed in or near explosive environments, and radiation may pass through them. Due to the inherent characteristics of radiation, it may ignite the surrounding explosive environment. Additionally, the presence of absorbers can significantly affect ignition. The country has clear explosion-proof testing andExplosion proof certificationStandard regulations. For light radiation equipment used in potentially explosive hazardous environments, the countryGB3836.22There are also corresponding explosion-proof technical requirements.
2、 There are four mechanisms by which light radiation may ignite:
1. After the surface or particles absorb light and radiation, the temperature increases, and under certain conditions, it can reach the temperature that ignites the surrounding explosive environment
2. When the wavelength matches the absorption band of the gas, a certain amount of combustible gas generates a hot spot
3. Radiation within the wavelength range of ultraviolet light causes oxygen molecules to dissociate, forming photochemical ignition
4. The laser at the focus of the strong beam directly causes gas decomposition, producing plasma and shock waves, which ultimately become ignition sources. Solid materials approaching the decomposition point will exacerbate this process.
What we are talking aboutGB3836.22Light radiation equipment is only applicable to the first1And No4The wavelength range of the point is380nm-10 µ mIgnite possible.
3、 Three explosion-proof types of optical radiation equipment
Explosion proof electrical optical radiation equipmentOpThere are three types of explosion-proof types available to prevent ignition caused by light radiation in potentially explosive environments. theseExplosion proof typeSuitable for all optical systems.
These three types of explosion-proof protection are:
Intrinsically safe optical radiation, explosion-proof type"Op is";
Protective optical radiation, explosion-proof type"Op pr";
Optical system with interlocking device, explosion-proof type"Op sh";
1Intrinsically safe optical radiation, explosion-proof type“Op is
（1）It refers to visible or infrared radiation that, under normal or specified fault conditions, does not ignite a specific explosive environment with the maximum energy generated. The energy, power, or irradiance that can cause visible or infrared spectra to be absorbed and ignited by the irradiated body are very small, and a safety level can be achieved by limiting the beam intensity. The principle of intrinsic safe light radiation is applicable to free radiation, without limiting the presence of absorbers in the environment, and has great flexibility in use.
（2）The optical radiation power or irradiance of different equipment categories and temperature groups are detailed in the table below
（3）The matching use of intrinsically safe optical radiation equipment
Optical devices that adopt the principle of intrinsic safety should provide fault protection measures when the power/energy exceeds the limit to prevent the occurrence of excessive light radiation in potentially explosive environments. And a hazard/hazard analysis should be conducted to determine when these devices are needed. Consider the failure mode of the light source, power isolation, and the presence of explosive environments to determine whether additional protection is required. Like laser diodes or light-emitting diodes(LED)If such a light source overheats under power exceeding fault conditions, it will malfunction. The thermal fault characteristics of certain light sources can provide necessary power over limit fault protection measures(10)Sample testing). A circuit with current limiting and/or voltage limiting devices installed between the light source and power supply can prevent power exceeding faults similar to intrinsic safety circuits.
（4）Protection level of intrinsically safe optical radiation equipment（EPL）
The protection measures for power exceeding faults should be consistent with the equipment protection level（EPL）Corresponding. aboutGaLevel devices, such as current limiting and/or voltage limiting devices, should be able to provide power over limit fault protection after applying two countable faults. To a thousandGbLevel equipment, apply a countable fault. aboutGcGrade equipment should be rated without considering any faults. The thermal fault characteristics of certain low-power light sources, such as light-emitting diodes, can be used for power exceeding fault protection at any level of protection.
2Protective optical radiation, explosion-proof type"Op pr"
（1）Protective optical radiation requires radiation to be limited to optical fibers or other transmission media, and assumes that radiation will not escape from the restricted range. The radiation limitation measures determine the safety level of the system. Conduct hazard analysis based on assumed conditions (fault conditions or normal operation) and propose safety requirements.
（2）Adopting explosion-proof type standards that comply with relevant requirementsCGB 3836When using the shell of the series, it is allowed to have an ignition source inside the shell, but it cannot ignite the external environment of the shell.
（3）Fiber optic internal radiation: Under normal operating conditions, fiber optic can prevent light radiation from escaping into the environment. For foreseeable faults, armor, conduits, cable trays, or cable conduits can be used to provide protection.
（4）Radiation inside the shell: The shell that may have an ignition source, if it complies withGB 3836The requirements for explosion-proof types specified in series standards (explosion-proof enclosures)"D"Positive pressure housingP“If there is a restricted breathing shell, there may be flammable radiation inside the shell. However, radiation escaping from the casing should be protected in accordance with the requirements of this section.
3Optical system with interlocking device, explosion-proof type“Op sh
（1）If the radiation limiting measures fail, the failure time is less than the ignition delay time, and the radiation becomes a non essential safety state in the presence of an interlocking disconnection device, then this type of protection should be adopted.
（2）The interlocking disconnection device should be activated according to the requirements determined by the hazard analysis. Relevant standards (such asGB/T 20438GB/T 21109)The prescribed method. Can be used to analyze the safety probability or hazard reduction coefficient of devices with different protection levels, as shown in the table3As shown.
4、 Applicable standards for explosion-proof certification of optical radiation equipment
1. Domestic standards:GB/T 3836.22-2017Explosive Environment Section22Part: Protection Measures for Light Radiation Equipment and Transmission Systems
2. International standard: DIN EN/IEC 60079-28-2015 Exploratory atmospheres - Part 28: Protection of equipment and transmission systems using optical radiation
5、 Applicability of optical radiation explosion-proof protection types
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