The New GAMP Good Practice Guide "Validation of Process Control Systems" (VPCS)

GMP News No. 372

GMP News
10 February 2004
 

The New GAMP Good Practice Guide
"Validation of Process Control Systems" (VPCS)

 
With GAMP 4, a standard for the validation of computerised systems wascreated that is by now established all over the world. Apart from thisdocument, Good or Best Practice Guides on particular aspects of thevalidation of computerised systems are or will be published by GAMP workinggroups. The most recent of these publications was the English version of the Good Practice Guide"Validation of Process Control Systems."

The Guide'sStructure

The starting point is the GAMP4 Guideline with its basic principles andmethods for computer validation. The Good Practice Guide takes up theseprinciples and demonstrates how they can be applied to the various types of systems in process control technology. For this purpose, modifications,extensions, but also reductions of the GAMP4 models are given.

The structure of this Guide is orientated towards that of GAMP4 andconsists of a main part and three sections with appendices. The main partincludes general information and basic concepts, like a life cycle that can beadapted to the system type and the system complexity. The first appendixblock compiles some specific topics (manufacturing parameters and dataspecifications for process control applications, software and hardwarecategories for process control systems, postal audits). Appendix block 2introduces a number of recommendations of the German GMA/NAMUR group for theexecution of projects that are subject to validation, for standard proceduresregarding operation and maintenance as well as for validation support bycontrol system functions and suppliers. Appendix block 3 containsinstructions by the US JETT group for writing user requirement specifications forembedded systems (skid mounted systems).

Process control systems are used for the automation of manufacturingprocesses (data collection, data supply, monitoring and controlling of themanufacturing process, linking superimposed systems for manufacturing control[MES] and general data processing [ERP]). Process control systems encompass a wide range of systems: from smallcontrols, e.g. built into manufacturing devices or equipment, to large,distributed control systems, like those for the operation of plants formanufacturing bulk materials or APIs. Correspondingly, the Guide definesthe two main categories "embedded systems" (including built-insystems) and "standalone systems" (with their own housing).

Embedded and Standalone Systems

Examples for embedded systems are microprocessors, SPSs or PCs that areused exclusively for controlling and monitoring manufacturing equipment.Usually, they are delivered as built-in parts of a unit or a machine. Forengineering, several disciplines are required; the life cycle documentationis largely created by the supplier.
Standalone systems are those systems that have their own housing, which is usually delivered separately for the connection tofield instrumentation and equipment. Often they are also connected tosuperimposed systems (e.g. Supervisory Control and Data Acquisition (SCADA),Manufacturing Executing Systems (MES) or Enterprise Resource Planning(ERP)). So, individual project engineering and co-ordination are necessary.

GAMP Principles

The GAMP principles (e.g. life cycle, planning, including risk and impactassessment, user-supplier relationship, specifications, traceability, draftreview, formal tests and verification, documented proof) can be transferredto these systems, however, some additional aspects have to be taken intoaccount. During the planning phase, not only the software and the computerhardware have to be taken account of, but also the complete fieldinstrumentation, the electrical devices and partly the mechanics of the plant.

The user requirement specification (URS) for a large application,as e.g. a DCS or SCADA, can be a separate document, for a small built-inapplication, it can be part of the device specification. In case of standalonesystems, the functional design specification (FDS) istypically a separate document that lists functions, features, and designrequirements for the DCS hardware and software. Like the URS, the FDS for anembedded system can be part of a superordinate device specification and referto devices, electric and mechanical elements. In both cases, it is oftenwritten by the supplier on the basis of the URS and is mostly a contractualdocument.

As process control systems often contain pre-configured elements, thedraft specifications indicate frequently how these elements and packageshave to be configured. Such specifications are laid down not only forsoftware (software modules) and computer hardware, but also for fieldinstrumentation and devices. They are illustrated by means of processdiagrams depicting the process routines as well as piping andinstrumentation diagrams (P&ID), which show the function and location of therelated control and monitoring loops.

Acceptance tests verify that the system works as it should andthat the URS and FDS requirements on software, hardware, and instrumentationare fulfilled. The tests are based on approved formal test specifications and areas a rule carried out jointly by the supplier and the user (4-eyesprinciple). The results are formally documented and released and can be usedas part of IQ and OQ. Especially in case of large systems, thesevery detailed tests are conducted in two steps. The Factory Acceptance Test(FAT) is carried out at the supplier's premises before delivery, forstandalone systems without field connection, if necessary withappropriate field simulation. The FAT already includes extensive tests ofthe system installation and function. The Site Acceptance Test (SAT)is meant to prove that the delivered system is undamaged and identical withthe system tested at the factory. Parts of the FAT may have to be repeated.In general, additional tests have to be carried out during the SAT when all field instruments,interfaces, and service connections have been established. These tests canbe conducted when the system is commissioned for operation.

Appendices

The GMA/NAMUR appendices compile recommendations for validatingprocess control systems. They comprise instructions for the execution ofprojects concerning new and revamped plants subject to validation (NE58),SOPs for operating and maintaining validated process control systems (NE71)as well as advice on validation support by use of control systems as supportfor planning and operation (NE72). 

A specific software model for process control systems is introduced.Software for control systems is characterised by the fact that, when thecontrol system is adapted to an individual application, programming isreduced to a minimum; instead, standard functions are used thatcan be modified individually by means of parameter sets. Such functions arecalled pre-configured software modules or pre-configured functions; they arenot application-specific. The pre-configured functions are, for their part,based on - also non-specific - control system operating systems, which maythemselves be based on commonly used standard operating systems. Thecontribution introduces the corresponding layer model. It showsschematically the mentioned software classes, their logic structure and the personresponsible for qualification.

For the purpose of project execution, the individual activities forplanning and qualification/validation, the input documents necessary forthis and the output documents to be created are represented in the form of atable, based on the life cycle model. A checklist serves for projectmanagement and indicates which activities have to be done when and by whomas well as the activities' degree of completion.

The generic standard operating procedures (NE71) concern processcontrol facilities (to be equated with the electrical, measuring and controlengineering facilities) of processing plants. They include 8 SOPsfor operation, maintenance and change of process control systems and supplement the GAMP4 SOPs. The topics are structure and maintenance of theprocess control system documentation, preventive maintenance and changemanagement, access control for process control systems, modem operation,re-verification, procedures in case of system failures and system faults,release changes, upgrade of hardware, update of firmware as well astraining.

Control systems can effectively support the qualification of thewhole plant or the validation of the manufacturing process, the operationand the maintenance of the validated state by means of appropriatefunctions. From the qualification requirements it results that - apart fromtheir reputation - suppliers of control systems can offer correspondingservices for the assistance in qualification. These functions and servicesare summarised in the recommendation "Validation Support by Use ofControl Systems" (NE72). They are classified in the recommendationaccording to their significance for validation.

The appendices by the JETT group (JETT: Joint Equipment Transition Team)deal with embedded systems. Originally, the group was founded by Lilly,P&U and Rockwell in 1996 in order to improve the documentation providedby equipment suppliers. To reach this aim, the group intended to developmethods for creating URSs and FDSs, project planning, draft specificationsas well as acceptance tests (hardware, software, system) at the supplier'sfactory and on site. The appendices contain instructions for the creationprocess of URSs, for integrated (embedded) control systems (built-in systems) as well asan example for the up-to-now created URS templates (18 of 30) for pure steamgenerators, fluid-bed driers, filling machines, blenders, freeze dryers,tablet coaters, multiple-effect stills, labelers, glassware washers,bioreactors, HVAC systems. Additional documents are planned for 12 furtherdevice categories. 

It remains to say that the GAMP principles can be applied efficientlyboth to embedded and to standalone control systems. Good EngineeringPractice and the usual initial operation activities can support the call forformal qualification.

 

Author:
Prof. Dr.-Ing. Hartmut Hensel, Hochschule Harz, Wernigerode, Germany 
The above text is a summary of his lecture given on the occasion of the CONCEPT HEIDELBERGseminar "GAMP 4" held on 17-18 November 2003. 
   

 

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