Terms, abbreviations, and concepts used across I&C project engineering — defined the way they are used on site, not the way a textbook defines them.
The final revision of an engineering document updated to reflect exactly what was installed in the field. The definitive record handed over to the owner at project completion.
A document listing every cable on a project — origin, destination, type, routing, and termination details. The master routing record for all field wiring.
A document that maps every process initiator (cause) to its required system response (effect). Bridges process safety and control system design. Produced during FEED or basic engineering.
The systematic process of verifying that installed equipment and systems meet design intent and are ready for operation. Includes loop checks, functional tests, and pre-startup safety reviews.
A final control element that regulates process flow by varying its opening in response to a controller signal. Selected by size, material, and trim based on the process datasheet.
A document specifying the technical requirements for a single instrument or piece of equipment. The primary document used for procurement. Every field on a datasheet is an engineering decision.
The primary process control platform — a networked system of controllers, I/O modules, and operator workstations that monitors and controls continuous process variables in real time.
The project phase where all engineering is completed to the level required for construction and procurement. Produces the full document set — drawings, datasheets, schedules, and specifications.
Intrinsic safety protection concept under IEC 60079. Limits electrical energy in a circuit to a level insufficient to ignite a hazardous atmosphere, even under fault conditions. The most common protection method for field instruments in Zone 1.
The project phase that defines scope, cost, and schedule with sufficient accuracy to support a final investment decision. I&C output at FEED includes the instrument index, P&ID, and control philosophy.
International Federation of Consulting Engineers, is the global representative body for consulting engineers, founded in 1913. It is best known for publishing standardized, internationally recognized construction and engineering contract templates.
Any sensing or final control device installed in the process area — transmitters, switches, analysers, valves. Sits at the bottom of the control loop, closest to the process.
A digital communication protocol between field instruments and control systems — replacing traditional 4-20mA wiring with a two-wire bus carrying multiple signals. Includes Foundation Fieldbus and Profibus PA.
The part of overall safety that depends on a system responding correctly to its inputs. Governed by IEC 61508 (generic) and IEC 61511 (process industry). Requires systematic design, verification, and lifecycle management.
A communication protocol that superimposes a digital signal on a standard 4-20mA analogue loop. Allows configuration, diagnostics, and secondary variables to be read without interrupting the analogue signal.
A structured, systematic examination of a process design to identify potential hazards and operability problems. The primary method for process safety review. I&C engineers attend to capture safety instrumented function requirements.
A software system that continuously records process data — every tag value, alarm, and operator action with a timestamp. The primary source of data for performance analysis, incident investigation, and regulatory reporting.
The operator interface to the control system — process graphics, alarm displays, and trend views. Design governed by ISA-101. A poorly designed HMI is a contributing factor in major process incidents.
A drawing showing the mechanical installation details for a field instrument — impulse piping, mounting, process connection, and isolation arrangement. The document a technician works from during installation.
The engineering discipline responsible for measuring process variables, controlling process conditions, and protecting personnel and equipment through safety systems. Covers everything from field sensors to control room systems.
The international standards body for electrical, electronic, and related technologies. Key I&C standards include IEC 60079 (hazardous areas), IEC 61511 (functional safety), and IEC 60332 (cable fire performance).
The document status indicating a drawing or document has been approved and released for use in the field. The highest approval status during the construction phase.
The master register of every tagged instrument on a project. Contains tag number, service description, line/equipment reference, signal type, and document cross-references. Every other I&C document traces back to it.
A protection technique for electrical equipment in hazardous areas that limits energy to safe levels. Requires IS barriers or galvanic isolators at the safe-area boundary. See also: Ex ia.
The primary standards body for instrumentation and automation. Key standards include ISA-5.1 (instrumentation symbols), ISA-18.2 (alarm management), and ISA-84 (functional safety, aligned with IEC 61511).
A field enclosure where individual instrument cables are terminated and consolidated onto multicore cables running back to the marshalling cabinet. Reduces cable bulk between field and control room.
A commissioning activity that verifies a complete instrument loop end-to-end — from field device through wiring, terminations, and I/O to the control system display. The definitive test before handover.
A document showing a single instrument loop in full detail — every device, terminal, cable, and signal from field to control system. The most detailed I&C drawing. Used for construction, commissioning, and maintenance.
A cabinet where field cables are terminated and cross-connected to control system I/O cables. The physical boundary between field wiring and the control system. Layout drives cable schedule and loop diagram structure.
A procurement document issued to vendors requesting a price and delivery for specified equipment. Includes technical datasheets, applicable standards, and commercial terms. Precedes the purchase order.
The Indian regulatory body that issues safety standards for the oil and gas industry. OISD standards are mandatory for Indian oil and gas facilities and are referenced alongside IEC and ISA on Indian subcontinent projects.
The primary process engineering document showing all process equipment, piping, and instrumentation with their interconnections. The origin document for every instrument tag. Governed by ISA-5.1 for symbol conventions.
A digital computer used for automation of industrial processes. Typically used for discrete logic and sequential control. Distinguished from DCS by architecture — PLCs are standalone units, DCS is a distributed network.
The physical quantity being measured or controlled — pressure, temperature, flow, level, or analytical value. The PV is what field instruments sense and what control loops act on.
The target value a control loop is trying to maintain. The controller compares the process variable to the setpoint and adjusts the output to minimise the difference.
A discrete level (1–4) specifying the required risk reduction of a safety instrumented function. SIL 1 is the lowest, SIL 4 the highest. Determined by risk assessment and achieved through design, verification, and management of functional safety.
An independent instrumented system designed to bring a process to a safe state when predetermined conditions are violated. Physically and logically separate from the DCS. Governed by IEC 61511.
The unique alphanumeric identifier assigned to every instrument on a plant. Constructed according to the Tag Numbering Procedure, based on ISA-5.1 conventions. Permanent for the life of the facility.
A document comparing vendor proposals against the technical requirements of an MRQ. Identifies compliant and non-compliant items, clarifications required, and a recommended vendor. Precedes purchase order award.
A field instrument that measures a process variable and converts it to a standardised output signal — typically 4-20mA or digital. The most common instrument type on a process plant.
A hazardous area classification where an explosive atmosphere is likely to occur in normal operation. Requires certified equipment with appropriate protection concepts — Ex ia, Ex d, Ex e, or equivalent. Defined under IEC 60079-10.