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Process Control System

Basic Guidelines for Process Control System Validation

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Most process plants consist of a combination of batch and continuous control functions. To fully document these functions, the following four components must be defined:

  • Analog (continuous) regulatory control loops (e.g. the level control loop of a distillation column)
  • Digital (discrete) control devices (e.g. control of motors, on/off valves, etc.)
  • Interlock logic, which defines the relative status of two or more devices to insure safe operation of the plant
  • Sequence control logic, which is the basis for batch process control. Actions are initiated in response to trigger events such as time, especially operating conditions, modification of product recipes, etc.

Analog loops and digital devices can be defined using a simple list (or database) of tag numbers, point descriptions, input/output (I/O) address, display information, measurement ranges, etc. Interlock logic can be documented using an interlock matrix. Sequences may be fixed or variable and even depend on the status of the process or on external factors such as market demand for different product grades.

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FDA Intention on Validation

The definition ‘Establishing documented evidence which provides a high degree of assurance that a specific process will consistently produce a product meeting its pre-determined specifications and quality attributes’ clearly identifies the FDA intention on validation. GxPs including good testing practice, good documentation practice and good engineering practice provide general principles and guidelines on validation requirements.

The GAMP Guide for Validation of Automated Systems in Pharmaceutical Manufacturing especially provides a detailed systematic approach on automation system validation but lacks many of the details on the programming side.

The Ranbaxy Affair: Insights in FDA Testings

The US Food and Drug Administration is authorized to perform inspections under the Federal Food, Drug, and Cosmetic Act, Section 704 (21 USC §374) ‘Factory Inspection’. Form FDA 483, ‘Inspectional Observations’, is a form used by the FDA to document and communicate concerns discovered during these inspections. Also referred to as ‘Form 483’ or merely ‘483’, it states thereon that it ‘...lists observations made by the FDA representative(s) during the inspection of your facility. They are inspectional observations and do not represent a final agency determination regarding your compliance.’

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