Glossary

The most common control algorithm in process industries. Three terms that adjust the output based on present error (P), accumulated past error (I), and rate of change (D).

An outer (master) loop manipulates the setpoint of an inner (slave) loop. Used when the slave responds faster to disturbances than the master can react.

Acts on a measured disturbance BEFORE it affects the process variable. Pairs with feedback PID for tight setpoint tracking.

Change in process variable per unit change in controller output, at steady state. The first parameter you need to tune any loop.

Time delay between a controller output change and the first observable response in the process variable. Loops with high θ/τ ratio are notoriously hard to tune.

When a PID controller saturates and the integral term keeps accumulating error. Anti-windup logic (back-calculation, conditional integration) is mandatory in any production controller.

Quantitative measure of risk reduction by a Safety Instrumented Function. Levels 1–4. Most plants need SIL 2; high-hazard processes need SIL 3.

The full chain — sensor + logic solver + final element — that performs one specific safety action (e.g. trip a reactor on high temperature).

Per IEC 61511, the SIS is independent from the BPCS. Different controllers, different I/O, different cabinets. Triconex, DeltaV SIS, Allen-Bradley GuardLogix are common.

Average probability that a SIF won”t perform its safety function when called upon. SIL 2 requires PFDavg between 10⁻³ and 10⁻². Lower is better.

Structured review of how a process can deviate from intended operation. The starting point of any functional safety project.

Determines how much risk reduction the existing IPLs (Independent Protection Layers) provide and what gap a SIF must fill.

The international standard for industrial cybersecurity. Defines security levels, foundational requirements, and zone/conduit architecture.

Hierarchical reference architecture (Levels 0–5) for industrial control systems. Still the foundation of every OT segmentation strategy.

Hardware/software that detects or causes change through monitoring/control of physical devices. PLCs, DCS, SCADA — distinct from IT (servers, networks, business apps).

Isolated network zone that mediates all data flows between IT (Level 4-5) and OT (Levels 0-2). Patch servers, historians, jump hosts live here.

The simplest, most ubiquitous industrial protocol. Request/response polling over standard TCP/IP. 50–500 ms typical scan rates.

Three classes: standard TCP, Real-Time (RT, ~10ms), Isochronous Real-Time (IRT, <1ms). Dominant in European motion control.

Industrial Ethernet built on CIP (Common Industrial Protocol). Class 1 cyclic implicit messaging for real-time data; Class 3 for explicit messaging.

Platform-independent, secure, semantically rich industrial protocol. Replacing OPC Classic. Includes PubSub for cloud-native architectures.