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Leveraging Batch Execution Software to Enable PAT

Tue, 06/26/2007 - 12:13pm
Process Analytical Technology (PAT) focuses on understanding a given process, and identifying and controlling its variability, with the aim of accurately predicting its outcome. Benefits of PAT include real time release of product, reduced cycle times, reduced work in progress, increased capacity and reduced human error, among many other financial benefits.

In a previous article (PAT Instrument Interface: Connecting with the Future of Pharma Manufacturing) I discussed the importance of instrument interface software in a PAT deployment. Instrument interface software is often overlooked in a PAT discussion but provides countless benefits which include interfaces for multiple PAT analyzers, processing of raw spectral data, closed loop control function and interface to plant and enterprise systems to disseminate PAT data.

Many life sciences facilities will also include other applications, such as batch control software in a PAT deployment. Integration of batch data and PAT data will be very important in providing a complete analysis of drug products to achieve process understanding and to realize the benefits of PAT. This article describes approaches to a unified PAT approach that includes integration with batch execution software.
A Combined Approach
Instrument interface software and batch execution software can be combined to provide a single system for experiments and production in a PAT environment.The role of instrument interface software is to first configure the spectral analyzer, retrieve spectral data from the analyzer, pre-process the spectral data and send the data to plant historian. Metadata including the analyzer configuration and process conditions may also be sent to the historian.

It is expected that in many cases a PAT environment will incorporate components adopting S88 methodologies. For example, the S88 physical and procedural models will be configured in a batch manager to include the PAT method. This will model the PAT instruments as either equipment modules or control modules. Procedural elements will be defined to execute PAT methods such as configuration, sampling, control and product release. The procedural elements will instantiate soft phases at runtime. These phases will communicate with the instrument interface software via OPC to initiate PAT related events such as instrument sampling and predictor calculations. Other phases will communicate with DCS/PLC systems under the control of the S88 co-ordination and activity model.

Instrument interface software readily integrates with batch control systems. Batch execution systems control other applications by sending commands using OPC. These commands may be received by the HMI/SCADA system or directly by controllers or the instrument interface solution. Once received, the receiving device will then perform the required function and handshake with other systems and the batch control system to indicate progress of the function and when the function is complete. At all times, related process and batch data may be logged to the plant historian.

The batch control system is in control of all equipment, including the analyzers. As part of the batch, the batch control system will acquire the analyzer and then send commands to calibrate, initiate a spectral scan and any other action required. All batch events will be logged to the batch journal. Batch data is stored in the batch journal. Spectral data is stored in Historian. Although these are constructed from separate database tables, possibly residing on separate servers, they form an integrated plant data repository. The tables are linked by using appropriate queries, either using a SQL query or a suitable reporting tool.

The Batch Manager will identify where equipment may be shared. Recipes will be configured as class-based where appropriate. At runtime, the manager will inform the soft phase of the instrument and unit identification (e.g. Blender in room #3 with mobile probe 2). The soft phase will be able to request the instrument to be installed and identified. This can be done using a barcode scanner or confirmation with an electronic signature. The soft phase will confirm the instrument ID with Proficy RX and store the audit trail in the batch journal.
Linking Batch Data And Spectral Data
Historian stores time-series data including spectral data from instrument interface software. Spectral data is stored with the analyzer name as part of the tagname, allowing for the spectral data to be uniquely identified against an analyzer. Spectral data is also stored with a timestamp, allowing for individual scans to be uniquely identified. The batch journal stores relational data, including event based data such as the start and end time of a batch. The batch data that is logged to the batch journal may be queried to determine the start and end times of batch; the results of this query may be used in a sub-query that is used to obtain the time-oriented data from the historian. The details of this query will be embedded in a report so the user will merely need to select a batch ID to obtain the spectral data for that batch.

The advantage of this approach is that it conforms to the relational database model and allows for normalization of the data. As a belt and suspenders approach, the batch ID may also be stored as metadata along with each spectral data scan within Historian. The batch identifier may be queried along with the time-oriented data so that at any time the batch identifier associated with that data is known. The specified data is stored in an optimized data historian, with the associated metadata (e.g. system audit trails) stored in a relational database. Both technologies are secure and are supplied with open technology interfaces for access to the data (e.g. for the rendering of human-readable reports).

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