Monday, April 16, 2012

Batch Relativity using OSI PI Batch

It's the year 2012 and still, I see customers with batch processes not using PI Batch... the proven system for navigating batches in PI. Truth be told, some of these customers are not using OSI PI, which is in itself a problem.

Batch Relativity is having the the start/endtimes of a time-window so that when you need to look at a trend, you can plot it without having to manually input the timestamps:

ProcessBook Trend Definition
Of course for time-windows in the recent past, you can use the arrows:

ProcessBook Trend Definition
But for precise review of trends in the past, there are few alternatives to manual input.

When I was first starting out as a fermentation engineer, I distinctly recall getting the Gantt charts from the Planning & Scheduling department at the morning meetings and typing in estimates of the start/end times from the 11x17" paper I got each morning thinking there must be a better way. And there is: you can programmatically specify start/endtimes from PI Batch into the PI Trends.

If you have a batch manager, you can purchase software that writes to the PI Batch Database. For example, if you have an Emerson DeltaV system, you can purchase the Emerson DeltaV Batch Interface (EMDVB) that reads from EVT files and inserts records into the PI Batch database. Otherwise, you can use the native PI Batch Generator (PI BaGen) Interface that comes with the PI Server.

PI Batch Generator

To use the PI Batch Generator, there are several pre-requisites. The first is having an Active Tag.... a tag whose value = 1 when the batch is running and a tag whose value = 0 when the batch is stopped:

PI Batch Active Tag
This is the minimum requirement for PI Batch Generator to work:

  • A PI Unit for each unit you wish to track batches
  • An Active Tag for each unit
  • PI Batch Generator Interface installed as a service

For bioreactors (i.e. fermentors), if you don't have a tag that specifically starts/ends a batch, the tag you can use is the pH Controller Mode. Here's why:

You are generally interested in what goes on in the fermentor when there's something going on. And something is going on when it is batched with media. And when it is batched with media, pH control is typically ON; which means the pH Controller Mode = 1. On the back end of the batch, you typically turn of pH control after transfer or harvest so pH Controller Mode = 0 when the batch ends.

You'll know that you've picked the right point when your process values change when Active Tag = 1 and they flatline when Active Tag = 0:

ProcessBook Trend PV tags
For other types of process equipment, be clever with your existing tags to figure out the best Active Tag; for example, volume tends to be a good Active Tag.

With the Active Tag, you have satisfied the only requisite for using PI Batch Generator, all others are optional:

  • Batch ID tag - a tag whose value equals the batch id at the time the batch is started.
    Typically some gibberish word that uniquely identifies this batch.
  • Product tag - a tag whose value equals the name of the product being produced. (e.g. 'HER2', 'E25', 'VEGF')
  • Procedure tag - a tag whose value equals manufacturing formula used

These values can be programmatically inserted in the event you don't want to consume tags for infrequent data.

Further reading:

Configure PI Batch!

No comments: