What is a Catalytic Gas Sensor? Working Principle, Advantages, and Usage Areas
1. Structure and Working Principle of Catalytic Sensors
Catalytic gas sensors generally consist of two ceramic beads called pellistors. These pellistors are tiny spheres with a catalyst layer containing platinum wire. However, only one of the pellistors in the system has a catalyst layer on it. The pellistor without the catalyst layer is called the reference pellistor. These two pellistors are connected to each other by a Wheatstone bridge.
The working principle of catalytic gas sensors is based on the oxidation of combustible gases. After the sensor encounters the gas, the working mechanism is as follows: First of all, the oxidation reaction starts on the pellistor with the catalyst layer, and the pellistor heats up. Thanks to this reaction, the coil heats up, and its electrical resistance changes. This change is detected as a signal from the sensor, and the presence of gas in the environment is detected.
Catalytic gas sensors require a warm-up period (up to 1 minute) before they start working. Since catalytic sensors measure the gas concentration depending on the temperature change, there is a reference pellistor so that the sensor does not react when the temperature increases even if there is no gas in the environment. When the temperature increases, there is no change in electrical resistance as both pellistors will heat up to the same degree. Additionally, due to its structure, other environmental factors such as humidity and pressure changes are prevented from causing erroneous measurements.
2. Technical Specifications of Catalytic Sensors
With the rapid development of today’s technology, T90 times for catalytic gas sensors have gradually shortened (T90 < 15 sec). Catalytic gas sensors are affected by the molecule size of the gas they measure. For example, the larger a molecule is, the greater the response time. They are also not suitable for working in oxygen-free environments.
The response of catalytic gas sensors is linear, giving accurate results up to 100% LEL. However, high concentrations of gas exposure will adversely affect the measurement results of catalytic sensors and cause them to give inaccurate results. This is because catalytic sensors need enough oxygen in the environment to measure accurately. Excessive presence of a flammable gas in the environment will negatively affect the measurement results, causing continuous measurement at high concentrations.
To avoid false alarms, it is recommended not to set the alarm level below 5% LEL for Methane (CH4), 10% LEL for Propane (C3H8) and Butane (C4H10), and 20% LEL for gasoline vapors.
3. Catalytic Sensor Poisoning
Certain chemicals are toxic to catalytic gas sensors. Their presence in the environment or contamination of the sensor in some way will cause the results to be incorrect. We can briefly summarize the substances that create a poison effect for catalytic gas sensors as follows:
- Silicones (e.g. waterproofing, adhesives, release agents, specialty oils and greases, certain medical products, commercial cleaning agents)
- Tetraethyl lead (e.g. leaded gasoline, especially aviation oil)
- Sulfur compounds
- Halogenated compounds
- Organo-phosphorus compounds (e.g. herbicides, insecticides, and phosphate esters in non-flammable hydraulic fluids)
4. Calibration and Maintenance
Catalytic gas sensors have an average gas detection life of about 2 years. This may decrease with increasing gas concentration in the environment. If the concentration increases to extreme levels and this exposure time exceeds 1 – 2 minutes, the sensor may be damaged and lose its sensitivity. Additionally, catalytic gas sensors must undergo calibration at intervals of up to 6 months. Gas detectors using catalytic gas sensors should be calibrated every 6 months to ensure continuous accurate measurements. Karf&Scoot gas detectors are delivered fully calibrated, and technical support is available to perform the calibration required during the normal lifetime of the product.
5. Applications of Catalytic Sensors
Catalytic gas sensors are used for the detection of flammable-explosive gases. Catalytic sensors are effectively used in our GD4R (household) and GD2G Catalytic (industrial type) series gas detection equipment developed under our Karf&Scoot brand.
For information about our Karf&Scoot GD2G Catalytic Sensor Gas Detectors and solutions suitable for your facility, you can review the product page or contact us.
Unauthorized copying and citation without permission is prohibited.
Karf&Scoot
