Safety light curtain selection starts with a hazardous motion and a person’s route to it, not a catalogue range or unit price. A curtain can be correctly certified yet placed too close to a machine that cannot stop in time. A beam can be interrupted while a person reaches the hazard from another side. Material flow can also tempt a team to bypass a protective function without defining when that exception is allowed. This guide turns the purchase into a specification and a set of verifiable factory and site acceptance criteria for machinery in Thailand.
What a safety light curtain does—and what its certificate cannot prove
A safety light curtain creates a detection field between an emitter and a receiver. Its purpose is to detect a person or part of a person entering that field as part of a safety-related system. A standard photoelectric sensor used to locate a product is not interchangeable with a protective device. IEC 61496-1:2020 sets general design and test requirements for electro-sensitive protective equipment; IEC 61496-2:2020 addresses active opto-electronic protective devices. The IEC descriptions explicitly leave the field dimensions, placement relative to a particular hazard and definition of the machine’s hazardous state to the application design.
The complete safety function includes detection, output, safety control, removal of motive power and stopping of the hazardous movement. It must describe faults, loss of power and restart. ISO 13849-1:2023 provides a method for designing and integrating safety-related control parts; it does not prescribe one required performance level for every machine. The risk assessment determines what is required in this application. A Type rating or a fine detection resolution is an input to that work, not its conclusion.
IEC 62046:2026 bridges product and application work. The IEC 61496 series addresses the electro-sensitive protective equipment as a product; IEC 62046 addresses selection, positioning, configuration and commissioning of presence-sensing protective equipment. The 2026 edition replaced the 2018 edition. Read it alongside ISO 13855 for placement while considering the machine, protective device, environment and human interaction. This article describes that role from the public scope; it does not infer clauses or numeric limits from the full text.
In a purchase specification, ask for two kinds of evidence separately: proof of the proposed device’s declared characteristics, and validation of the installed safety function. This prevents the common statement “it is Type 4, therefore the press is safe” from replacing an engineering argument about stopping time, access routes and control behavior.
Map hazardous tasks and approach paths before requesting prices
ISO 12100:2010 provides the principles and method for machinery risk assessment and risk reduction. Include production, setup, jam clearing, cleaning, maintenance and recovery after a stop. For a press with automatic feeding, a hand loading a part from the front, a hand reaching the die from the side, a person passing beneath a conveyor and a technician inside the machine are different paths. One optical plane does not automatically protect them all.
Record the hazardous motion and stored energy, approach direction, body part that can reach it, operating mode, possibility of standing beyond the field and conditions for restoring power. Check for ejected material, hot surfaces and other hazards that require physical containment. The public scope of ISO 13855:2024 distinguishes separation distance from protection against ejected matter or mechanical failures. A light curtain senses entry; it is not a physical shield. Combine it with guards and other measures when the risk assessment calls for them.
Walk the actual access paths. Steps, carts, temporary work tables and changed material positions may create overreach, crawl-under or walk-around routes that a drawing misses. If a person can pass the beam and remain between the field and the hazard, define how restart is prevented and how the space is checked. Photograph the opening and document plan and side views before quotations. These details affect the guard work, wiring and floor space quoted by suppliers.
Compare seven specifications on the same basis
Ask each bidder to fill the same table against the same hazard scenario and machine conditions.
| Item | Specify or confirm | Acceptance evidence |
|---|---|---|
| Detection capability | Body part to detect; effects of blanking and other settings | Model data, configuration, suitable test-piece results throughout the field |
| Field height and range | Effective top/bottom, opening width, reflective surfaces and adjacent emitters | Installation drawing, alignment record, site photographs |
| Standards and performance | Applicable IEC 61496 edition, device Type, required whole-function performance | Manufacturer documentation and safety-function validation |
| Response time | Device, controller, power switching and machine stopping | Device data plus measured total stop behavior |
| Environment | Dust, water, temperature, vibration, cleaning and stray light | Site condition sheet, device ratings, trial results |
| Functions | Restart interlock, external device monitoring, muting, blanking | Logic drawing, backed-up settings, fault tests |
| Maintenance | Alignment, cleaning, replacement and change authority | Instructions, spares and training record |
The required detection capability follows from the body part and access path, not a desire to buy the smallest number on a datasheet. Check the effective sensing area rather than the physical bar length. A high lower edge permits crawling under; a low upper edge or a side gap may permit bypass. The needs of a hand-loading aperture and a full-body material passage differ.
Do not use the curtain’s Type to stand in for the whole circuit. Specify where both safety outputs go, how faults are detected and how contactor or drive failures are handled. Our safety PLC validation guide covers the control-system part in more detail. Here, the purchase must define the data and tests passed from the curtain supplier to that system.
Survey the real mounting location for oil mist, reflecting surfaces, neighboring transmitters, welding light, cleaning agents and cable damage. Obtain the exact model’s current operating instructions. The SICK deTec4 instructions, for example, set product-specific requirements for design, alignment, commissioning and restart interlock. Those values cannot simply be copied to a different product.
ISO 13855 safety distance depends on the installed machine
ISO 13855:2024 addresses the positioning and dimensioning of safeguards relative to human approach. For a light curtain, review approach direction, detection capability, the distance from field to hazard, total response and all routes over, under or around the field. Avoid copying an older simplified formula from another project into a calculation labeled “2024 edition.” Pilz’s explanation of the revised standard describes the more structured calculation and the need to account for the response of the complete system.
Measure or justify the machine stopping behavior under the operating conditions that matter: load, speed, brake condition and settings may change it. The device response time alone omits the controller, switching devices and machine motion. Record the instrument, conditions, results and the machine configuration. If a later modification changes stopping time, the earlier layout calculation must be revisited.
Moving the field closer can improve loading ergonomics, but is unacceptable when the hazard cannot stop before a person reaches it. Moving it too far away can create space in which a person stands behind the field, introducing restart risk. Evaluate distance, space occupancy and restart as one design. Our robot safety fence article provides related context for robot cells; its numerical example must not be transplanted to another machine.
Pilz’s Safety Distance Calculator supports conventional applications using ISO 13855:2024, but Pilz explicitly says it is an aid for expert users and does not cover all special approaches, reaching over or under, or dynamic cases. Keep its inputs, assumptions, standard edition, measured stop time, exclusions and reviewer with the calculation report. A screenshot alone is not acceptance evidence.
Specify muting and blanking as controlled exceptions
When material crosses the field, the correct requirement is a defined exception for a defined process—not a permanent bypass. A muting specification should describe permitted material, direction, sensor sequence, time window, abnormal stop, reverse travel, restart and who may change settings. FAT and SAT should test a person following material, a stalled load and a failed sensor, not just a normal pallet passage.
Blanking ignores a defined object within part of a detection field. SICK’s definition distinguishes fixed blanking, whose location and size are defined, from floating blanking, where size is defined but position may move. Confirm the detection capability that remains and whether configuration changes response time. The SICK C4000 Select instructions are one example of a model whose response-time calculation accounts for configuration and blanking. Use the manual of the selected model for actual values and redo the distance assessment after changes.
Back up the approved setting, identify the responsible approver and test every relevant product changeover. Define the reset button and restart sequence so clearing the beam does not by itself start hazardous motion. The deTec4 manual, as one product example, separates reset from the subsequent start command. The application designer must validate the actual circuit and local requirements.
What belongs in a Thai factory request for quotation
Headquarters may approve specifications, the machine builder may design the cabinet and a local integrator may install and run SAT. Put the boundaries in writing: who measures stop time, who validates the safety function, who updates as-built drawings and who owns the configuration backup. A lit indicator is not a signed-off safety function.
Request a hazard and task list, opening drawings, operating modes, material-flow description, required stop behavior, fault state, proposed product data, stop-time measurement plan, ISO 13855 positioning assessment, bypass prevention, circuit diagrams, safety-function description, FAT/SAT protocol, backed-up settings, spares and operator training. A substitute model must trigger review of response time, effective height, detection capability, wiring and diagnostics.
Compare equipment, brackets, fixed guarding, control modifications, wiring, measurement, FAT/SAT, downtime for installation, training and spare parts as separate quotation lines. Lowest device price is not necessarily lowest installed cost. Conversely, the risk assessment may show a simpler fixed guard is sufficient. Compare alternatives only after each meets the required protection. If existing stop time or dimensions are unknown, state the assumption and identify the work that may change after measurement.
Deliver formal design records and practical site instructions in languages the responsible staff can use. Demonstrate the test method on the real machine and identify whom to contact after a fault. Check applicable Thai legal, customer, site and contractual requirements for the specific installation; citing an international standard alone is not a legal compliance determination.
FAT and SAT: evidence that supports acceptance
FAT tests the intended control logic before shipment. SAT verifies the installed geometry and actual machine stop under site conditions. For each test record the expected state, observed result, pass/fail decision, tester, date and configuration version.
| Test | Record | Failure example |
|---|---|---|
| Field coverage | Suitable test piece at top, middle, bottom and edges | Undetected gap or crawl-under route |
| Stopping | Interruption in every relevant mode | Hazardous motion continues |
| Stop time and placement | Measured machine result against approved calculation and location | Slower stop or insufficient distance |
| Fault response | Relevant cable, power, device and switching faults | Fault goes undetected during operation |
| Restart | Beam recovery, reset and start as separate conditions | Automatic start on beam clearance |
| Material flow | Muting sequence, reversal, stall and following entry | Human passage remains permitted |
| Change | Retest after settings, brackets, device or software changes | Old report reused without review |
Use a test piece appropriate to the selected resolution and manufacturer instructions. A hand or arbitrary stick is not a complete field test. Include abnormal material sequences, not only ideal operation. Conduct tests involving hazardous movement under controlled, competent supervision. Record measurement equipment, machine load and settings, and photographs with reference dimensions. Acceptance means the agreed safety function works against the agreed hazards on the real machine.
Preserve the function after handover
Alignment can shift, lenses can become dirty, brackets can loosen, guards can be removed and workpiece dimensions can change. Define periodic checks from the adopted product instructions, risk assessment, use and environment. Observable items include the intended stop on beam interruption, detection at the field boundaries and retained restart behavior. The factory sets an appropriate interval; a universal monthly or annual interval is not asserted here.
On failure, use a controlled stop, isolation, investigation, repair, retest and release process instead of allowing an informal production bypass. Manage spare emitter/receiver models, firmware, settings and connector compatibility. Alignment after replacement alone does not prove that separation distance and restart behavior remain valid. If a bracket or position moved, repeat the affected tests.
Treat a requested muting or blanking change as an engineering change. Review its effects on risk, detection, stop time, placement and test coverage. Update evidence before returning the machine to service. Change control gives production a safe way to improve the process rather than silently invalidating the original acceptance.
A practical sequence for comparing bids
Connect the specification to observed work
Procurement should collect evidence of how people approach hazards before requesting a preferred sensor model. Automatic production may involve little contact, while setup requires frequent hand access. Maintenance may use a different door and cleaners may approach near the floor with tools. Observe each mode safely and combine worker interviews, stop histories, near misses, temporary steps and material-bin positions. Map routes from a safe state rather than asking someone to demonstrate unsafe access.
For each hazard scenario, write the initiating condition, hazardous motion, approaching person, point at which detection must occur, required stopped state and restart condition. “Stop when a hand reaches the die” is incomplete if it does not identify which axis stops, whether pneumatic pressure remains or whether a part coasts. Observable descriptions make FAT/SAT measurements possible. If a proposed safety function has no matching test, acceptance may show that the device reacted without proving the agreed risk reduction.
Also define normal work that should continue. If material must be distinguished from a person, document its size, direction, stalls, reversals and closely spaced loads. When production would routinely need to defeat a safeguard, redesign the layout or material handling before purchase. Productivity requirements may shape an acceptable design, but they do not justify reducing required detection capability.
Manage uncertain stopping and installation data
Existing machines often lack a measured stop time at quotation stage. Label an assumption as an assumption, set a measurement point before final installation and define what happens if the measured time exceeds the design input. State who supplies the instrument, which machine conditions are tested, which result is adopted and who approves it. The buyer can then see whether a failed distance assessment requires moving the bars or changing guards and working space.
Do the same for physical dimensions: floor to opening, hazard depth, clearance to neighboring equipment and interference with pipes or columns. Agree when the as-built measurements will be taken. Moving a conveyor or fixture can change where material interrupts the field. Adjustable brackets do not guarantee that the final position matches the approved distance calculation. Record a reference point, fixing method and final position in SAT photos, so a bracket struck later can be restored to an approved location rather than aligned by eye.
Make acceptance a repeatable procedure
Acceptance is more than a demonstration that an indicator changes color when a beam is blocked. Specify the test piece, test order, field locations and expected machine state. Mark top, bottom, middle and side positions on a drawing so checks do not depend on one operator’s height or dominant hand. For material passage, challenge the design with a stopped load, reversal, two close loads and a person following material. A following person is not inherently blocked during muting; test that the configured sequence detects or stops the challenge under the designed conditions.
If a test fails, link the cause, changed part or setting, tests affected by the change and the retest results. Even optical alignment can change field edges or reflection conditions. A control-software change calls for renewed stopping, restart and fault checks. Tie every record to the equipment and configuration revision, and ensure the purchaser can see that no unresolved acceptance item remains at handover.
Before opening the price columns, check that the bidders addressed the same hazardous motions, access paths and operating modes. A proposal that covers only front hand entry is not comparable with one that also covers a side opening and a person following material. Then check the stop-time evidence: measured on this machine, taken from a manufacturer document or merely assumed. If assumed, allocate responsibility and cost for correcting the layout when SAT measures a longer stop. Confirm whether opening dimensions and field height came from the actual installation or an old drawing.
Ask each bidder how the curtain behaves during setup, cleaning, tool changes, manual feed, maintenance and jam clearing. A statement that it stops in automatic mode leaves critical intervention tasks unanswered. If a bypass or key override is proposed, require its permitted conditions, alternative safeguards, records and return-to-service procedure. Separate logic that FAT can test from actual stopping and access routes that SAT must verify. Name the party who corrects failures, approves retesting and prevents production restart while an acceptance item remains unresolved. Finally compare the complete cost, including spare devices, cleaning, configuration restoration, training and reassessment after future changes.
Record why each rejected option was rejected. A low-cost model may need two emitter/receiver pairs to cover the opening, adding interference controls and wiring. An easy-to-mount model may leave no practical cleaning access in an oily area. These are application decisions for this opening, operating pattern and maintenance team, not universal rankings of manufacturers. Keeping the assumptions makes later relocation or a supplier change easier to reassess.
List acceptance deliverables individually rather than asking for “all drawings”: the hazard-to-safety-function matrix, stop-time record, placement calculation, as-built mounting dimensions, circuit and I/O list, configuration identifier, raw FAT/SAT results, nonconformity and corrective-action history, and operator inspection procedure. Give each document an equipment number, model, revision, date and approver. Otherwise it can be impossible to show that the tested settings are the same settings handed over.
Feed near misses and failed routine checks back into the risk assessment after start-up. “No accident yet” is not evidence that the safeguard is adequate. Reassess any newly discovered access path or stopping delay and revalidate placement, guards, controls or procedures as necessary. The purchase should establish a way for site findings and machine changes to update the engineering record.
FAQ: safety light curtain selection and deployment
Is selecting Type 4 enough?
No. Type is a device characteristic. The installed function still needs a risk-derived performance requirement, suitable detection capability and placement, validated stopping, control behavior, protection against bypass and restart management.
Can an online ISO 13855 calculator finalize the safety distance?
It can support a competent design. The actual stopping behavior, approach routes, reach-over and crawl-under routes, occupancy behind the field and applicable standard edition must still be assessed and recorded.
Is finer resolution always the best choice?
Select for the body part and approach to be detected, effective field dimensions, material passage and operating environment. Confirm the final configuration, including any blanking, and revisit response time if it changes.
What should quotations include besides the curtain price?
Include mounts, guards, safety-control work, stop-time measurement, installation downtime, FAT/SAT, backup, training and spares. Give all bidders the same hazard scenarios and acceptance tests.
Does following international standards settle legal compliance in Thailand?
No single article can determine compliance for a particular machine. Check applicable law, machine classification, customer, industrial estate and contract requirements for the site. International standards support design and evidence but do not replace that check.
Conclusion
Select a safety light curtain by defining the hazard, approach path and whole safety function first. Then evaluate IEC 61496 device information, ISO 13855:2024 placement and actual stopping, and the safety-related control design under ISO 13849-1. Specify muting and blanking as controlled exceptions, and accept the installation only with documented FAT/SAT evidence covering faults and restart. Preserve the result through inspection and change control.
If you are considering a safety light curtain for an existing machine in Thailand, you can contact TOMAS TECH even at the specification stage. Opening drawings, site photographs, hazardous motions and any stop-time data provide a useful starting point for defining the purchase and acceptance criteria.
