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Educational use: ElectraCore supports learning and preliminary checks. It does not replace a competent electrician or engineer. Verify results, equipment data, and current local regulations before installation or live work.
Courses/Industrial Control & PLCs/Safety Systems

lesson · 9min · Lesson 18 of 30

Light curtains and safety interlocks

Course syllabusCourse overview
01Motor Starters
  1. ReadDOL starter: main and control circuit
  2. ReadStar-delta starter: wiring and timer
  3. ReadSoft starters: operation and parameters
  4. ReadVariable speed drives: inverter drives
  5. quizMotor starter quiz
02Contactors & Overloads
  1. ReadContactor construction and ratings
  2. ReadAuxiliary contacts and interlocking
  3. ReadThermal overload relays: setting the dial
  4. ReadElectronic overloads and motor protection relays
  5. exerciseContactor circuit problems
03Control Circuit Diagrams
  1. ReadIEC 60617 symbols: reading control diagrams
  2. ReadLadder diagrams: European and American styles
  3. ReadDrawing a full DOL control circuit
  4. ReadForward-reverse motor control
  5. exerciseDiagram reading exercises
04Safety Systems
  1. ReadEmergency stop requirements: IEC 60204
  2. ReadSafety relays and safety PLCs
  3. ReadLight curtains and safety interlocks
  4. ReadSafe isolation: EAWR and multi-energy control
  5. quizSafety systems quiz
05PLC Fundamentals
  1. ReadWhat is a PLC and where is it used?
  2. ReadPLC architecture: CPU, I/O modules, power
  3. ReadLadder logic basics: contacts and coils
  4. ReadTimers and counters in ladder logic
  5. exerciseWriting a simple motor control program
06Panel Layout & Installation
  1. ReadPanel design: layout and component spacing
  2. ReadCable management inside panels
  3. ReadLabelling, ferrules, and documentation
  4. ReadPanel testing and commissioning checklist
  5. quizFinal assessment
Lesson · 9min
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In this lesson

PurposeCore theoryWorked exampleKnowledge checkSources

In this lesson

PurposeCore theoryWorked exampleKnowledge checkSources
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ElectraCore lesson handout

Light curtains and safety interlocks

Industrial Control · Lesson 18 · Advanced

AdvancedReview: professional review pending

Purpose

Integrate light curtains and guard interlocks using stopping performance, reach/access geometry and validated reset/muting logic.

Before you beginMotor starter circuits · Machine hazard and protection fundamentals

Learning objectives

  • Read state and cross-references
  • Separate standard control from safety functions
  • Analyse faults and reset behavior
  • Validate the complete input-logic-output path

A light curtain detects intrusion but does not physically restrain a person. Its location must ensure hazardous motion reaches a safe state before anyone can reach the danger zone.

MACHINE SAFETY FUNCTION PATHMACHINE SAFETY FUNCTION PATHSUPPLYSTARTERmotor · loadshort circuit · overload · command · interlock · isolation

Core theory

Determine safety distance using total response time of sensor, logic, outputs and machine stop plus the applicable approach-speed and resolution terms. Measure worst-case stopping performance and account for deterioration.

Prevent reach over, under, around or between beams and access behind the sensing field. Guard interlocks must address defeat, alignment, locking where run-down persists and escape/restart conditions.

Muting, blanking and bypass are distinct functions with strict conditions, indication and anti-circumvention logic. Reset must have a safe view and cannot initiate motion.

Terms, symbols, and units
TermMeaningSymbolUnit
ESPEElectro-sensitive protective equipmentNot applicableNot applicable
ResolutionSmallest specified object reliably detectedNot applicableNot applicable
MutingTemporary automatic suspension under defined safe conditionsNot applicableNot applicable
Worked exampleA supplied formula is S=K×T+C, with K=1600 mm/s, total T=0.35 s and C=120 mm.

Assumptions: Symbols and terminal designations are defined by the supplied drawing set; Required safety performance comes from the machine risk assessment.

  1. Travel: K×T=1600×0.35=560 mm.
  2. Add: S=560+120=680 mm.
  3. Verify: Confirm the formula/terms for the exact application and prevent reach-around/access-behind.

Illustrative minimum distance is 680 mm under the supplied method; complete geometry and validation still govern.

Reasonableness check: The conclusion is checked across normal, demand, fault, reset and restart states rather than inferred from one component label.

Common mistakes
  • Reading a contact in the energized instead of defined normal state
  • Using an ordinary PLC bit as an unvalidated safety function
  • Assuming emergency stop isolates every energy source

Where this appears in practice

Clear diagrams and validated safety functions let competent people build, test, diagnose and modify machinery without losing the intended protective behavior.

SafetyDo not bypass guards, light curtains, interlocks or safety outputs for production or diagnosis. Control hazardous electrical, pneumatic, hydraulic, gravitational and stored energy; isolate, lock off and prove dead using the site procedure before access.
Local code checkUse the current machine risk assessment, applicable type-C standard, IEC/BS EN 60204-1, ISO/BS EN ISO 13849-1 or IEC/BS EN 62061 design route, IEC 61496 where applicable, Electricity at Work Regulations, site lockout procedure and manufacturer validation instructions. BS 7671 Section 514 identification/notices does not by itself define or authorize the complete safe-isolation procedure.

Knowledge check

Can a light curtain be placed from catalogue response time alone?

No. Use total measured stopping performance and applicable geometry/reach terms.

Answer: No. Use total measured stopping performance and applicable geometry/reach terms.

Practical exercise

Evaluate a guarded cell for detection coverage, total response time, reset view, muting sequence and access behind protection.

Summary

  • A diagram is a state model plus physical cross-reference
  • Safety performance belongs to the complete function
  • Stop, emergency stop and isolation are distinct

Sources and review

  • IEC 60204-1:2016+AMD1:2021: Electrical equipment of machines: IEC; 6.1; International
  • ISO 13849-1:2023: Safety-related parts of control systems: ISO; 2023; International
  • IEC 62061:2021 with current amendments: Functional safety of machinery control systems: IEC; 2021; confirm current consolidated version; International
  • IEC 61496-1:2020: Electro-sensitive protective equipment: IEC; 2020; International
  • Electricity at Work Regulations 1989: UK Legislation; Current official text; Great Britain

Editorial review date: 2026-08-22. Professional electrical review is pending.

Educational material for learning and preliminary checks. Verify current local requirements and exact equipment instructions. This lesson does not replace competent professional work.

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