GLOSSARY / PLAIN LANGUAGE

The terms,
in plain words.

Short definitions of the control, power and reliability terms used across this site, for readers who work outside industrial engineering.

2N

Two complete, independent sets of equipment, each able to carry the whole load on its own.

Advanced process control

Control software that adjusts many related settings together to keep a process closer to its best operating point than individual control loops can.

Alarm flood

More alarms than one operator can read and act on, commonly more than about ten in ten minutes, so the important ones are lost in the rest.

Alarm suppression

Hiding an alarm from the operator while a related condition makes it redundant, such as the consequences of an equipment trip already alarmed.

Analyzer

An instrument that measures what a process stream is made of, rather than just its pressure, temperature or flow.

Chattering alarm

An alarm that repeatedly raises and clears in a short time, usually because a measurement hovers around its limit.

Common-cause failure

One cause that disables both halves of a redundancy at once, such as two pumps that draw power from the same bus.

Cutover

The moment operation switches from an old system to its replacement.

DCS (distributed control system)

The computer system that monitors and controls a continuously running plant, spread across many controllers rather than one central computer.

Dead time

The delay between a control action and the first sign of its effect on the measured process.

Deadband

The margin a measurement must move back past its limit before an alarm clears, so small fluctuations do not toggle it.

Factory acceptance testing

Testing equipment and its software at the supplier, against criteria agreed in advance, before it is shipped and installed.

Gas chromatograph

An analyzer that separates a gas sample into its components and measures how much of each is present.

Historian

A database built to record plant measurements over time, so trends and past events can be reviewed later.

Hypervisor

The software layer that runs virtual machines on a physical server and shares its processors, memory and storage between them.

IEC 61511

The international standard for designing, operating and maintaining safety instrumented systems in the process industries.

Maintenance window

A planned period when equipment may be taken out of service for work, agreed in advance with the people who run the plant.

Modbus

A long-established communication protocol that industrial devices use to exchange readings and commands.

N+1

One more unit than the load needs, so any single unit can fail or be taken out for maintenance without losing capacity.

PID controller

The most common feedback controller: it adjusts an output using the present error, its accumulated history and how fast it is changing.

PLC (programmable logic controller)

A rugged industrial computer that controls a machine or part of a process with fast, repeating logic.

Real-time optimization

Software that repeatedly works out the most economical operating conditions for a plant and passes them to the control systems.

Ride-through

How long equipment can keep running on stored energy, such as a UPS battery, after its supply is lost.

RTO (recovery time objective)

The longest a service may stay unavailable after a failure before the interruption becomes unacceptable.

Safety instrumented system

An independent control system whose only job is to bring a process to a safe state when a dangerous condition is detected.

Telemetry

Measurements sent continuously from equipment to a system that stores and displays them, so problems can be seen as they develop.

UPS (uninterruptible power supply)

Batteries and power electronics that keep equipment running for a short time when its normal supply fails.

Virtualization

Running several separate computers as virtual machines on one physical server, so they share its hardware.

For how these ideas fit together, read the engineering principles.