Protecting Pellistor Sensors
Pellistor sensors are commonly used to detect combustible hydrocarbon gases. Since it reacts linearly to many flammable gases, it provides reliable and economical solutions when there are multiple flammable gases in the environment. However, pellistor sensors also have some weak points that should be considered.
Most important disadvantage of pellistors is their poisoning and loss of sensitivity due to various chemicals commonly used in the industry.
Contaminant compounds, such as lead, silicones, phosphate, and sulfur-based substances can cover the catalyst surface. They can create a coating on sensor that can permanently decreases the sensitivity of the sensor and can lead to full sensor failure. When the sensor is poisoned and exposed to flammable gas, it does not react at all. In this case, although the presence of gas in the environment reaches a dangerous level, the detector cannot generate alarm warnings, continues to operate as if the environment is safe and causes no preventive action to be taken.
Such compounds emitted in the detector's location can impair the sensitivity of the sensor without you realizing it. If silicon compounds can be found in the environment due to application or process, the detectors should be calibrated periodically and their sensitivity should be checked. Poisoning can only be identified by a bump test or calibration.
Also volatile organic compounds (VOCs) and hydrogen sulfide (H2S), can be easily absorbed by the catalytic bead catalyst. The absorption of these compounds creates a blockage in the reaction to flammable gas on the catalyst that may result temporary loss of sensitivity. In this case sensor react as inhibited and measured gas level will be lower than actual. Sensor inhibition can be resolved after a period of exposure to fresh air.
Exposure of high concentrations of combustible gases can create problems as well. Catalytic bead of pellistor sensor may shift off of the baseline zero value and display a %LEL value even in clean air. The catalyst surface can be damaged that can result sensitivity lose and sensor unable to measure gas level correctly. In case of longer exposures the sensor may permanently damaged, and no longer be able to detect gas. Pellistor sensors exposed to high gas concentrations must be re-calibrated to make sure that the sensor is fully functional.
In order to protect the detectors and to use them in a healthy way for a long time, environmental conditions should be carefully monitored and calibration or response testing should be done regularly.
Prosense is ready to assist you in determining and performing the maintenance procedure needed for your devices.