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Amperometric gas sensors are commonly used in air quality monitoring in long-term measurements. Baseline shift of sensor responses and power failure may occur over time, which is an obstacle for reliable operation of the entire system. The purpose of this study is to check the possibility of using PCA method to detect defected samples, identify faulty sensor and correct the responses of the sensor identified as faulty.

In this work, the authors present the results obtained with six amperometric sensors. An array of sensors was exposed to sulfur dioxide at the following concentrations: 0 ppm (synthetic air), 50 ppb, 100 ppb, 250 ppb, 500 ppb and 1000 ppb. The damage simulation consisted in adding to the sensor response a value of 0.05 and 0.1 µA and replacing the responses of one of sensors with a constant value of 0 and 0.15 µA. Sensor validity index was used to identify a damaged sensor in the matrix, and its responses were corrected via iteration method.

The results show that the methods used in this work can be potentially applied to detect faulty sensor responses. In the case of simulation of damage by baseline shift, it was possible to achieve 100% accuracy in damage detection and identification of the damaged sensor. The method was not very successful in simulating faults by replacing the sensor response with a value of 0 µA, due to the fact that the sensors mostly gave responses close to 0 µA, as long as they did not detect SO₂ concentrations below 250 ppb and the failure was treated as a correct response.

This work was inspired by methods of simulating the most common failures that occurs in amperometric gas sensors. For this purpose, simulations of the baseline shift and faults related to a power failure or a decrease in sensitivity were performed.

Although there are many journalistic accounts of ongoing political events narrating about pro-democratic or antiauthoritarian movements, such as strikes, riots, and protest letters, not many scholarly analyses devote attention to the longitudinal analysis of the preceding events that lead to a spur of protests. Not many scholars account or are able to account for the activity of political dissidents that is often hidden, purposely censored, and covered from public eye. Most frequently, until the street strike and riots, the degree of spread of dissident activity within a country is unknown to scholars. It is equally difficult to find information about the national and international networks that political activists form to gain support and acceptance of their acclamations, propositions, and calls for political or economic reforms. Furthermore, only access to dissident press allows researchers to glimpse the activity of existing organizations looking at issues censored by existing governments.