PLC, HMI and instrument loop

A programmable logic controller (PLC) reads instruments, runs the equipment’s sequence and interlocks, and drives valves and motors; the human-machine interface (HMI) shows the process and takes operator input; an instrument loop is the chain from sensor through transmitter and wiring to the controller and display.

Under Annex 11 the control application is validated and its infrastructure qualified, with risk-based decisions on validation and data integrity controls (Principle, 1). Changes, including configuration, are made only under a defined procedure (10), access is restricted to authorised people (12), and measuring and control equipment is calibrated at defined intervals (Chapter 3, 3.41).

Where it sits: Inside or beside every automated GMP machine: sterilisers, washers, filling lines, lyophilisers, water systems and HVAC.

• —Equipment control and sequencing
• —Interlocks and alarms
• —Batch and cycle data recording where the HMI stores records

In the reference facility: Automation & control room, Processing & formulation suite, Aseptic filling & isolator line, Plant utilities, HVAC & energy centre

Not covered on this page: Manufacturing execution and enterprise systems; Safety instrumented systems, which have their own standards.

• 01PLC (processor and I/O). Executes the control program.
• 02HMI or SCADA. Displays, alarms, operator actions and, sometimes, data records.
• 03Field instruments and transmitters. Sense the process and convert to signals.
• 04Actuators. Valves, motors and heaters driven by the controller.
• 05Program and configuration backups. Allow a known version to be restored.

Connects to: Equipment it controls; Historian or data collection; Network and remote access; Calibration and maintenance systems.

• 01Temperature sensor (RTD or thermocouple). An example loop: sensor, transmitter, scaling and display, calibrated end to end. Watch for: sensor not at the location that matters (cold spot, load centre).
• 02Pressure transmitter (gauge or absolute). An example loop where range and scaling must match the configured values. Watch for: gauge and absolute values compared directly.

• 01Alarm limit and delay (setpoint, engineering units or s (delay)). Configured per tag under change control, with its basis and required response.
• 02Audit trail record (attribute, entries per change: who, what, when, why). For GMP-relevant changes made at the HMI, based on risk (Annex 11, 9).

SPEQ publishes no universal alarm or acceptance values: they depend on the process, the product and the site’s own qualification.

• 01Interlock: Equipment interlocks. Constrain actions — doors, sequences, permissives — and are tested in qualification.
• 02Procedure: Change and configuration management. Program and configuration changes only under a defined procedure (Annex 11, 10).
• 03Procedure: User access management. Individual accounts and roles; creation, change and removal recorded (Annex 11, 12).
• 04Procedure: Loop calibration. Calibration at defined intervals, sensor to display (Chapter 3, 3.41).
• 05Procedure: Business continuity. Documented and tested arrangements for a system breakdown (Annex 11, 16).

An alarm asks for a response; an interlock stops an action; a safety function protects people and has its own risk basis.

• 01Specification. User and functional requirements based on risk (Annex 11, 4.4); Inventory and system description for critical systems (4.3).
• 02Testing. Factory and site acceptance tests; Interlock, alarm and error-handling tests (Annex 11, 4.7); Loop checks.
• 03Operation. Access records and reviews; Calibration records; Backups and restore checks (Annex 11, 7.2).
• 04Change and periodic. Change records with impact assessment (Annex 11, 10); Periodic evaluation (11).

• 01EU GMP Annex 11: Computerised Systems — European Commission (EudraLex Volume 4), 2011, in operation 30 June 2011 (revised draft consulted from 7 July 2025, not in force). European Union; in force. Supports: Validation and qualification (Principle, 4); risk management (1); data checks (5); backups (7.2); audit trails (9); change and configuration (10); periodic evaluation (11); security (12); business continuity (16).
• 02EU GMP Part I, Chapter 3: Premises and Equipment — European Commission (EudraLex Volume 4), 13 August 2014, in operation 1 March 2015. European Union; in force. Supports: Calibration of measuring, recording and control equipment at defined intervals (3.41).