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Data Acquisition and Handling Systems

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CEM system analyzers do not stand alone, but are part of a larger system as seen in Figure 1‐1. The assembly of analyzers is coordinated and controlled to provide emissions data that are subsequently recorded and reported. These roles were all originally considered part of the data acquisition and handling system (DAHS or DAS). Today, control functions are commonly separated from the DAHS by using data loggers, programmable logic controllers (PLCs), or separate microprocessor systems. This simplifies the CEM system by providing more flexibility for both system control and data acquisition and reporting.

Hardware used in CEM recording and reporting systems has evolved from the now archaic strip chart recorders to computer systems integrated into the plant distributive control system and the plant local area network, corporate wide area network, or intranet. In special cases, remote terminal units are used to provide emissions data to environmental control agencies either continuously on a real‐time basis or on demand.

CEM software has evolved significantly, principally due to the demands of the U.S. EPA Acid Rain Program. Requirements to report all emissions data plus plant operational data, on a quarterly basis, have led to sophisticated multitasking programs, having the capability of editing and back‐filling data according to prescribed algorithms. Today’s programs offer flexibility to both CEM system operators and environmental engineers in evaluating data quality and in preparing internal and external reports.

Programming tends to be customized to meet the demand of each plant installation with flexible and user‐configurable programs, making this task somewhat easier. The integration of CEM system data into plant distributive control systems and information networks has become a larger task. This requires considerable coordination between plant information technology personnel, plant engineers, the CEM system integrator, and the data acquisition system provider. This is often the most difficult job associated with the installation of a new CEM system.

Continuous Emission Monitoring

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