Continuous, batch, discrete: the three worlds of production
Every plant belongs to one of three families, based on what it makes and how. This distinction drives the choice of automation, tools and standards.
Why this distinction comes first
Before talking about controllers or standards, you must know what the plant produces and how. Three families exist, and everything follows: the type of control system, the tools, the skills, the applicable standards.
| Continuous | Batch (by lots) | Discrete | |
|---|---|---|---|
| Flow | uninterrupted | by recipes, lot after lot | counted parts |
| Examples | refining, cement, paper | pharma, fine chemicals | automotive, electronics |
| Typical tool | DCS | DCS/PLC + recipes | PLC, robotics |
| Dedicated standard | — | ISA-88 | — |
| Key metric | stability, yield | batch traceability | OEE |
The continuous process
A flow that never stops: refining, petrochemicals, power generation, paper, cement. Material enters, is transformed and leaves continuously. You regulate quantities (temperature, pressure, flow) at all times, with control loops by the hundreds. Typical tool: the DCS. Key challenge: stability — a stoppage propagates through the whole chain and is very costly. Start-up and shutdown are long, delicate, sequenced.
The batch process
You make by recipes, lot after lot: fine chemicals, pharma, food, paints. You charge, transform per a recipe, discharge, clean, start again. Each lot is traced. Typical tool: DCS or PLC + recipe management. Dedicated standard: ISA-88, which structures recipes and phases. Key challenge: batch traceability and reproducibility.
Discrete manufacturing
You produce objects counted one by one: automotive, electronics, machines, packaging. The part moves along a line, undergoes operations, is assembled, tested. Typical tool: the PLC and robotics. The key metric is Overall Equipment Effectiveness (OEE), the product of three factors:
A line available 90% of the time, running at 95% of its rate, with 99% good parts, shows an OEE of . This single indicator reveals where productivity is lost: downtime, micro-stops or scrap.
Many plants are hybrid
Reality often mixes all three: a food plant runs batch (cooking) then discrete (packaging). A refinery is continuous but its tank farm follows a management logic. Recognising which logic applies to which part of the plant is a core skill of the automation engineer.
The link between production and enterprise management (orders, stock, planning) is structured by the ISA-95 standard.