How To Choose The Correct Type Of Thread Electrode

How to choose the correct type of Thread Electrode
At present, our understanding of toxic and harmful gases is also more focused on combustible gases, can cause acute poisoning of gas (hydrogen sulfide, hydrogen cyanide, etc.), and some common toxic gases (carbon monoxide), oxygen and other detectors, Therefore, this article will first focus on the introduction of such detectors, and the current situation on the various types of screw electrode (inorganic / organic) applications to make recommendations.

Classification and principle of Thread Electrodes:

The key component of the threaded electrode is the gas sensor. Gas sensors from the principle can be divided into three categories:

A) The use of physical and chemical properties of the screw electrode sensor: such as semiconductor (surface control type, volume control type, surface potential type), catalytic combustion, solid thermal conductivity and so on.

B) the use of physical properties of the threaded electrode sensor: such as heat conduction, optical interference, infrared absorption and so on.

C) The use of electrochemical properties of the screw electrode sensor: such as the potential of electrolysis, Jia Dani battery, diaphragm ion electrode, fixed electrolyte and so on.

According to the harm, we will be toxic and harmful gases into combustible gases and toxic gases two categories. Because of their nature and harm, the detection means are different. Combustible gases are the most dangerous gases encountered in industrial applications such as petrochemicals. They are mainly organic gases such as alkanes and certain inorganic gases such as carbon monoxide.

Combustible gas explosion must have certain conditions, that is: a certain concentration of combustible gases, a certain amount of oxygen and enough heat to ignite their fire source, which is the explosion of three elements (as shown in the upper left of the explosion triangle), missing one No, that is, the lack of any of these conditions will not cause a fire and an explosion.

When the combustible gas (steam, dust) and oxygen mixed and reach a certain concentration, in case of a certain temperature of the fire source will explode. We put the combustible gas in case of fire source explosion concentration is called the explosive concentration limit, referred to as the explosion limit, generally expressed in%. In fact, this mixture is not in any mixing ratio will occur on the explosion and have a concentration range. As shown in the figure on the right. When the combustible gas concentration is lower than the LEL (minimum explosion limit) (combustible gas concentration is insufficient) and its concentration is higher than the UEL (maximum explosion limit) (oxygen shortage) will not explode. The different combustible gases of LEL and UEL are different (see the introduction of the eighth issue), which is very important when calibrating the instrument. For safety reasons, we should generally give an alarm when the combustible gas concentration is 10% and 20% of the LEL, where 10% LEL is said. Warning warning, and 20% LEL called dangerous alarm. This is why we will be combustible threaded electrode, also known as the LEL detector. It should be noted that the LEL detector shows 100% of the concentration of combustible gas is not 100% of the gas volume, but reached 100% of the LEL, which is equivalent to combustible gas minimum explosion limit, if it is methane, 100% LEL = 4% of the volume concentration (VOL). In the work, to LEL way to measure these gases detector is our common catalytic combustion detector. Its principle is a two-way bridge (commonly known as Wheatstone bridge) detection unit. In which one of the platinum wire bridge coated with catalytic combustion material, no matter what kind of flammable gas, as long as it can be ignited by the electrode, platinum wire bridge resistance will be due to changes in temperature changes, this resistance changes with Combustible gas concentration into a certain proportion, through the instrument's circuit system and the microprocessor can calculate the concentration of combustible gas.

Directly measured the volume concentration of combustible gas thermal conductivity of the VOL electrode can also be obtained in the market, at the same time, there have been LEL / VOL combined into a detector. VOL combustible detector is particularly suitable for measuring the volume (VOL) concentration of combustible gases in an environment of hypoxia (oxygen deficiency).

Toxic gases can be present in the production of raw materials, such as most organic chemicals (VOC), may also exist in the production process of various parts of the by-products, such as ammonia, carbon monoxide, hydrogen sulfide and so on. They are the most dangerous risk factors for the staff. This hazard includes not only immediate harm, such as physical discomfort, morbidity, death, etc., but also includes long-term harm to the human body, such as disability, cancer and so on. For these toxic and harmful gas detection, the need for threaded electrodes, which is our developing countries should begin to cause full attention to the problem.


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