What？Sensors could be poisoned？

Do you know that sensors will be poisoned?  they need protection too.

During the daily use of catalytic combustion sensors, it is inevitable that they will come into contact with chemicals and vapors from household cleaners, lubricants, and other specialized chemicals mixed in the air. These substances can potentially act as toxic agents or inhibitors for different types of sensors, often leading to a partial or complete loss of sensor sensitivity.

In the case of poisoning, such an occurrence can be defined as a permanent failure, whereas inhibition can still be salvaged and recovered in fresh air.

Although today's sensors possess strong resistance to poisoning, it is still crucial from the perspective of prolonging their service life to minimize exposure to potentially harmful environments as much as possible.

What are the causes of catalytic combustion sensor poisoning?

The most harmful gases to combustible gas sensors are silicone-containing compounds, such as silanes, silicone resins, and silicates. Even a few ppm of these substances can significantly degrade sensor performance. These compounds are widely used in various applications, including lubricants, cleaning agents, abrasives, adhesives, cosmetic and pharmaceutical creams, as well as silicone seals and gaskets. Additionally, lead-containing compounds, particularly petrol with tetraethyl lead, can seriously diminish the sensitivity of sensors, especially for compounds with high ignition points like methane.

In addition, high concentrations of halogenated hydrocarbons, when exposed to high heat conditions within the catalytic head, can decompose into HCl, potentially leading to corrosion of the sensor and consequently diminishing its measurement signal. Additionally, compounds such as hydrogen sulphide, carbon disulphide, dimethyl disulphide, trimethyl disulphide, phospholipids, and nitro compounds (including nitroalkane hydrocarbon) can undergo oxidation to form mineral acids, which can also cause corrosion of the sensor. Moreover, exposure to hot organic acids (such as acetic acid) or acidic gases (like HCl and sulphuric acid vapours) may result in the corrosion of the sensor.

Halogenated hydrocarbons are found in the solvents of all types of degreasers and cleaners. These dreaded halogenated hydrocarbons can likewise be released through overheating of polymers, in PVC welding rods. All of these mentioned substances can have a detrimental effect on catalytic heads. Typically, silicone compounds are regarded as poisonous and hydrogen sulphide is regarded as an inhibitor. However, all of the above-mentioned substances can reduce the sensitivity of the catalytic combustion sensor to varying degrees. Some compounds may react at increasing temperatures in the catalytic head, and the mechanism by which these cause poisoning of the sensor is even more complex.

How can catalytic combustion sensors prevent poisoning?

1. Ensure that the filter in front of the sensor of the combustible gas detector is working effectively and that it is replaced weekly or immediately after the instrument has been exposed to toxic gases.

2. When the sensor of the combustible gas detector is exposed to a toxic gas environment, it is necessary to take a cleaning sample, replace the gas line and gaskets.

3. Minimize the time the sensor of the combustible gas detector is exposed to air, and take measures to switch off the instrument when it is not used for a longer period of time.

4. Especially in toxic environments, it is necessary to reduce gas flow or use diffusion-type instruments to ensure the timely diffusion of toxic gas concentrations in the detection environment.

5. Actually, the best protective measure is to prevent the sensor poisoning of the combustible gas detector, especially in terms of installation, usage, and maintenance of the instrument. It is necessary to spend some time obtaining a deeper understanding to truly achieve prevention for the sensor.

What are the ways to prevent poisoning installation and maintenance?

To avoid introducing toxic substances into the instrument:

1. Do not use injection-moulded plastic parts, which may contain silicone releasing agents.

2. Do not use silicone rubber and silicone seals as instrument accessories, as these materials can release some harmful gases. And do not use the instrument where these materials are processed.

3. Do not install, commission or store the instrument in a place where sanding compounds, cleaning agents or lubricants containing silicon are used. Most furniture polish contains silicon.

Installers and maintenance personnel should not use cosmetics containing silicone oil components:

1. Silicone oil lubricants are extensively used in gas valves or regulators in gas dilution equipment; therefore, do not use such equipment to detect flammable gases.

2. Always use non-toxic epoxy resins and adhesives. Avoid using sticky labels on or inside the instrument, as many adhesives contain silicone.

3. Always use original parts for replacement.