Batch processing is arguably the most difficult manufacturing there is. Discrete assembly operations have thousands of parts to source, manage and track. Continuous processes have to tweak and tune based on raw material variables and operate in spite of hazardous conditions and the specter of “abnormal situations.” But batch processors have to manage multiple steps in a process that can start then be suspended while something else happens; vary by temperature, ingredient, humidity or chemical reaction; and is regularly changed when planned or unplanned setpoints are reached. And don’t forget that since the final product is often ingested by humans, it must not be allowed to sicken or kill anyone.
That being said, I contend that the manager of an oil refinery’s got nothing on the guy charged with formulating medicines or processing and packaging a million pots of yogurt. What is abnormal situation management for continuous processes is a normal—and very difficult—operating procedure for batch.
Batch processing is all about state-based control, enforcing rules about moving from where I am to where I want to go in a process, in defined steps. Those needing to learn the basics should seek out tools and documents explaining the ISA-88 standard, which lays out a structure for equipment modeling, phase definitions, recipe development and controller programming. Those who understand the basics and want to know how to actually program their batch control systems will soon have a new tool from Rockwell Automation, maker of PlantPAx, FactoryTalk Batch, Logix Batch & Sequence Manager and other batch processing software.
Rockwell Automation’s Batch Starter Kit is both a reference manual filled with documentation and a collection of copy-and-paste code samples for running phase logic in Logix controllers.
“We’re establishing a philosophy, a way to think about the batch model, about running the phase logic, all the way down to the objects. It may not be your philosophy, but that’s okay. It’s a starter kit. It’s a blank slate for letting you do better,” explained Bruce Lightle, process control consultant, during a session at Rockwell Automation’s Process Users Group (PSUG) meeting in Anaheim. “Our advice is going to hit the mark 60-80 percent of the time, then you can change it for your philosophy.”
For example, the kit will ask you to consider when you want to lock a phase in program mode. “That helps you realize you ought to be putting in locking,” said Lightle. “Locking often gets ignored at the device, phase and unit level. If a phase is running, phase devices should be locked. If the phase is in a holding state, those devices should be released.”
The kit was done with Rockwell’s PlantPAx Logix Batch & Sequence Manager (LBSM) product in mind. “The goal is to develop a phase library that you can run with procedural sequences you code yourself,” Lightle said. He anticipates that the kit will be continually updated with additional phases, including others that run natively in FactoryTalk Batch.
Code examples in the kit include phases calling phases and in-state models, and they follow the Logix Phase Manager standards, which conform to ISA-88 standards. Examples in the starter kit are primarily built in ladder logic, with one example built in sequential function chart (SFC). Why? “Because I’m a ladder logic programmer and I did most of the development,” said Lightle. “We’ll get others working on it now that the first bunch of examples are done.”
A question from one PSUG attendee showed how eager users are for a way to more quickly get started with automated batch processing—and highlighted how code development ideas are changing. This young engineer from pharmaceutical maker Genentech asked if there is some open source, online forum where batch control code can be shared, copied and reused “so I and others don’t have to reinvent the wheel.”
“Well, the forum is right here in this room, and the code is in our new Batch Starter Kit, but today you have to pay for it,” answered the Rockwell Automation speaker.
Those ready to go beyond the basics should investigate batch analytics software. These tools to compare batches and uncover potential problems in real time, enabling users to compare ideal, “golden” batches to other batches to better understand how variables affect the current batch.