Phthalocyanine sensor for nitrogen oxide detection - has heating phase constantly superseding measurement phase, when sensor resistor exceeds or falls below the predetermined value

摘要

In a phthalocyanine sensor for NOx detection in air, in which the phthalocyanine layer operates at an optimised temp. during the measurement phase and is cyclically purified by periodic temp. increase. The measurement phase (11) is constantly superseded by the heating phase (12) when the sensor resistance (2) drops below a predetermined value (3) or when the sensor resistance change with time (4) exceeds a predetermined value. The resistance change with time is used as a measure of the NOx concn. and an electronic processing and control unit is used for periodically determining the sensor resistance, changes in the measuring time period being compared with stored values which describe the amount of change as a function of the gas concn. over time. ADVANTAGE - Optimal use is made of the available measuring time since the heating phase is controlled according to the NOx loading of the sensor layer.