Glossary · Batch and process operations
Sequence table
Also known as: Step table
German: Ablauftabelle
In process control engineering, a sequence table is a tabular way of defining a sequence, in which rows or columns represent steps and the table specifies the conditions for each step and the actions or outputs set in it.
- Batch control
In one sentence
A sequence table defines a control sequence as a table of steps, their conditions and the actions or outputs set in each step.
Example
The sequence table for a filter backwash lists six steps with the valves opened, the pump state and the time or level condition to move on.
How it applies
- Engineering: Some control systems provide sequence tables as a configuration method; engineers can also use them in specifications before implementing the sequence, for example in a Sequential function chart (SFC).
- Commissioning: Tables are easy to check step by step against the running plant and against the process engineer's intent.
- Operation: Operators can follow the current step if the HMI shows the table with the active step highlighted.
- Documentation: Sequence tables are a compact format for functional specifications and operating descriptions. The documentation team should keep step numbers and names identical to the controller and HMI, and state what happens when a step is interrupted.
Sequence table vs. sequential function chart
A sequence table lists steps, conditions and actions in rows and columns. A sequential function chart is a graphical IEC 61131-3 language with steps, transitions and actions, better suited to branching sequences.