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We report on the realization, calibration, and test outdoor of a 19-inches rack 3-units sized Quartz Enhanced Photoacoustic Spectroscopy (QEPAS) trace gas sensor designed for real-time carbon monoxide monitoring in ambient air. Since CO acts as a slow energy relaxer when excited in the mid-infrared spectral region, its QEPAS signal is affected by the presence of relaxation promoters, such as water vapor, or quenchers like molecular oxygen. We analyzed in detail all the CO relaxation processes with typical collisional partners in an ambient air matrix and used this information to evaluate oxygen and humidity-related effects, allowing the real CO concentration to be retrieved. The sensor was tested outdoor in a trafficked urban area for several hours providing results comparable with the daily averages reported by the local air inspection agency, with spikes in CO concentration correlated to the passages of heavy-duty vehicles.

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This paper presents concepts of operator- and system-centered diagnostics as well as approaches for the implementation of standardized diagnostics in modular process units - prepared by the  ZVEI/NAMUR working group 4.1.1. Availability is a critical issue in the operation of process plants. Maintenance should not signify a substantial cost driver. By combining a MTP-like and NOA-like diagnostic channels, the balance between the encapsulation in operation (via MTP) and the necessary transparency for efficient diagnostics (via NOA) can be handled. In this paper, insights of both channels are presented to allow for open discussions about these concepts.

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