Page 247 - Wastewater Solids Incineration Systems

Instrumentation and Control 209

9.0 DATA ACQUISITION SYSTEMS DATA INTEGRITY

Unfortunately, the more data acquisition is automated, the more likely operators tend
to ignore its validity, fail to question the “data integrity chain,” or subsequently fail
to correct errors in the data set. This is manifested in two distinct areas—system spec-
ifications and system utilization by the owner. First, the owner must oversee the
specification, design, and selection of a data acquisition system with data integrity
features at a highly detailed level. Second, the owner must implement the use of the
data integrity features specified in the product. Many systems and their underlying
databases have been designed and purchased that do not anticipate the need for the
owner to review data and subsequently mark data as valid/invalid. (For example, a
field pH probe may be challenged during calibration with unknown or standard
solutions and sends that signal to the system database. While the pH reading might
have been (or not been) accurate, it was transmitted properly and entered into the
database. It was not a representative signal from the process and must therefore be
annotated for validity and possibly correction or augmentation with appropriate
data from another instrument. Because this validity management need was not antic-
ipated, a vital functionality is absent that would allow the owner to perform exami-
nation and correction of the data, supplementing correct data gained from another
instrument or source. If data are modified or augmented, it must be done through a
comprehensive feature that provides an audit trail documenting the “who, what, and
when” of such changes. Though this feature is typically integrated to laboratory
information management systems (LIMS), it is not at all common for plant-wide data
acquisition systems. The details are not trivial, however. Sample data in LIMS are
entered infrequently, whereas continuous process data are typically measured mul-
tiple times per second.
Automatic data acquisition and storage must be compared with the familiar wet
sample chain-of-custody questions implemented through LIMS systems:
• Where have your data been?
• Have they been collected and stored as they should?

• Have they been tampered with?
From a regulatory standpoint, this information provides the basis for demon-
strating a facility’s compliance with regulations—or visible evidence of noncompli-
ance. Data quality should be carefully considered regarding whether it shows careful
compliance or willful noncompliance. The difference may result in significant finan-
cial loss or even serve as the basis for criminal charges. The ability to store, access,