Get in touch with QJKH Company
Updated June 2026 · Reviewed by the QJKH technical team
Light curtain blanking is the function that let you tell a safety light curtain to ignore part of its protective field so a fixture, conveyor, or workpiece can sit in the beams without stopping the machine. It’s the single most useful, and most misunderstood, feature on a presence-sensing safeguard, because the moment you blank a beam you also change how well the curtain detects a hand. This guide explains the three types of blanking, how blanking differs from muting, how it forces you to recalculate your safety distance, and how to configure it without quietly defeating your own protection.
Quick answer: Blanking suspends a defined part of a safety light curtain’s protective field so a permanent or repeating object can occupy those beams while the rest of the field keeps protecting the operator. It is an optional, configured function of an electro-sensitive protective equipment (ESPE) device under IEC 61496, and because it reduces detection capability, it can require a longer safety distance.
Quick Specs: Blanking at a Glance
| What it does | Suspends a defined zone of beams in the protective field |
| Types | Fixed · Floating · Reduced-resolution (programmable) |
| Governing standards | IEC 61496-1/-2, IEC/TS 62046, ISO 13855, OSHA 1910.217 |
| Effect on resolution | Enlarges the minimum detectable object (degrades detection capability) |
| Safety distance impact | May increase via ISO 13855 term C = 8 × (d − 14) mm |
| Configured by | DIP switch, key switch, or software tool with teach-in |
What Is Light Curtain Blanking?
A safety light curtain projects a grid of infrared beams from a transmitter to a receiver, and when an object interrupts enough beams the safety outputs (OSSDs) de-energize and stop the machine. Blanking is the configured exception to that rule: it lets a defined set of beams stay broken without triggering a stop.
Whenever the field is interrupted elsewhere, that machine stoppage still keeps an operator out of the hazardous area. Engineers also call it the blanking function, and on most light curtain systems it’s disabled by default until an integrator deliberately enable and teaches it.
In practice, the purpose is simple. Many machines have something that must sit inside the protective field, a conveyor rail feeding a hydraulic press, a clamping hose, a robotic fixture, or a sheet of stock. Without blanking, that permanent obstruction would hold the curtain in a tripped state and the machine would never run. With blanking, the curtain tolerates the known object while still protecting the point of operation around it.
IEC 61496-2 classifies these curtains as active opto-electronic protective devices (AOPDs), and blanking is a defined option within that standard rather than a vendor add-on. QJKH engineers size each blanked zone deliberately, because reducing the grid changes the ISO 13855 safety distance and the reach-through risk, not just the wiring. There is one detail every integrator should internalize: when you blank a portion of the light grid, the blanked area extends the full depth from transmitter to receiver. It is a tunnel through the protected area, not a small patch on one face, which is exactly why blanking is treated as a safety-related decision, not a convenience setting.
💡 Pro Tip
Blanking is a function of the curtain itself, not the safety relay or controller downstream. If you are still mapping out the control chain, our guide to the safety light curtain system shows where the curtain, output signals, and reset logic fit together.
The Three Types of Blanking: Fixed, Floating, and Reduced Resolution
Most vendor glossaries list “two types of blanking.” In the field there are three, and the difference decides whether your object can move. Fixed blanking holds a static set of beams open at one location. Floating blanking lets a defined number of adjacent beams be broken anywhere within a range, so the object can travel. Reduced-resolution (programmable) blanking teaches the curtain the object and tolerates it while coarsening the detection grid. Choosing the wrong one is a common cause of nuisance stops and of over-blanking.
| Blanking type | What it ignores | Object motion | Resolution effect |
|---|---|---|---|
| Fixed blanking | A fixed set of beams (a blanking window) | Stationary object only | Local blind zone; rest of field unchanged |
| Floating blanking | N adjacent beams, anywhere in a range | Object may move (coil stock, clamp hose) | Coarsens detection by the floated beam count |
| Reduced resolution | A taught object profile | Repeating object presence | Enlarges minimum detectable object globally |
Type definitions per IEC/TS 62046 and field practice.
What is the difference between fixed and floating blanking?
Fixed blanking ignores a set of beams at one location, so it suits an object that never move, such as a guard rail or a permanent bracket through the field. Floating blanking ignores a set number of adjacent beams but lets their position shift within a range, so it suits an object that travels, like coil stock that rises and fall.
A useful rule: if the object is bolted down, fix it; if it wanders, float it. One advanced variant, floating blanking with compulsory object presence, inverts the logic: the blanked beams must stay occupied, so removing the object faults the curtain and prevent a restart.
📐 Engineering Note
Floating blanking is defined by a beam count, not a millimetre gap. On a 14 mm-resolution curtain, every beam you float widens the smallest object the grid can still catch. QJKH ENT Type 4 curtains, for example, offer 14, 30, and 40 mm resolutions across a 160–1827 mm protective height with a response time of ≤14 ms, so the floated count directly trades detection against flexibility. Keep it to the minimum the application need, one or two beams, and verify it against the object’s real travel, not its nominal size.
Blanking vs Muting: The Difference Engineers Mix Up Most
Blanking and muting both let objects pass a safety light curtain without stopping the machine, but they aren’t interchangeable. Blanking suspends part of the field continuously for a stationary or repeating object; muting suspends the entire field briefly for a transient transport event, and it relies on additional sensors to decide when it’s safe. Engineers on PLC forums report the two are routinely confused, and that support varies by manufacturer, so getting the distinction right at the design stage matter.
| Dimension | Blanking | Muting |
|---|---|---|
| Scope | Part of the protective field | The entire protective field |
| Duration | Continuous (always active) | Temporary (a timed window) |
| Trigger | Taught zone of beams | ≥2 independent muting sensors |
| Typical use | Fixture or stock permanently in the field | Pallet or AGV passing through |
| Press rule (OSHA) | Not cycle-gated | Permitted on the upstroke only |
Press-mode muting rule per OSHA 29 CFR 1910.217(c)(3)(iii)(d).
Standards back this up. On mechanical power presses, OSHA permits muting, “bypassing of the PSD during the upstroke of the press slide”, only “for parts ejection, circuit checking, and feeding,” per OSHA’s Machine Guarding eTool. Blanking, by contrast, runs throughout the cycle. If you need to suspend protection only during one phase of the machine cycle, you want muting; if you need to tolerate a fixed obstruction at all times, you want blanking. For a deeper treatment of the timed-bypass case, see our guide to muting a safety light curtain.
“The mistake we see most is a plant using blanking where the application actually needs muting, or vice versa. Blanking is for the object that lives in the field; muting is for the object that passes through it. Get that backwards and you either fight nuisance stops or you leave a gap open longer than you should.”
How Blanking Changes Detection Capability and Safe Distance
Blanking is not free. Every beam you blank or float enlarges the smallest object the curtain can still detect, its detection capability, or resolution, d. Because the minimum safety distance under ISO 13855 depends directly on d, blanking can push the curtain farther from the hazard. ReeR and other ESPE makers flag this explicitly: using the blanking function “may need a recalculation of the safety distance due to the modified detection capability.” This is the catch that thin guides skip.
ISO 13855 sets the minimum distance as S = K × T + C, where K is the approach speed (2000 mm/s for a hand reach, or 1600 mm/s in some cases), T is the total stop time of the machine plus the curtain’s response time (typically 14–50 ms), and C is an intrusion term tied to resolution. For a vertical curtain detecting fingers or hands (d ≤ 40 mm), C = 8 × (d − 14) mm.
📐 Engineering Note: The Resolution Penalty Rule (worked example)
Take a 14 mm finger-detection curtain on a machine with a 0.20 s total stop time, K = 2000 mm/s.
• Baseline: C = 8 × (14 − 14) = 0 mm → S = 2000 × 0.20 + 0 = 400 mm.
• Now apply floating blanking that degrades effective detection capability to 30 mm: C = 8 × (30 − 14) = 128 mm → S = 400 + 128 = 528 mm.
Blanking just added 128 mm to the distance the curtain must sit from the hazard. Run the same arithmetic with your own stop time before you blank a single beam.
Exact numbers depend on your measured stop time T, the approach direction, and machine geometry, so treat the example as a method, not a fixed answer, request a real stop-time test on your press before finalizing the mount. The takeaway holds regardless: blank more, and you must either accept a longer safe distance or add complementary guarding. For the underlying detection grid, our explainer on finger and hand protection resolution shows how 14 mm, 30 mm, and 40 mm grids compare.
How to Configure Blanking on a Safety Light Curtain
Blanking is configured at the curtain itself, through DIP switches, a key-switch teach box, or a software tool, and on most light curtain systems it ships disabled. An integrator enable it, teaches the blanked zone by blocking the relevant beams in teach mode, verifies the visual indicator, then locks the setup under supervisory control before returning the unit to run mode. It’s a deliberate, recorded change, not a casual one.
Behind that sequence sit several choices. A selector switch sets the mode of operation, and the software tool lets you programme the blanked beams, run diagnostics, and confirm the curtain’s specification before you commission it, the selection, configuration, and commissioning steps that IEC/TS 62046 sets out for presence-sensing protective equipment. Teaching actuates the chosen beams; removing the object can deactivate them or fault the curtain, based on how blanking is set up. Decide too whether the curtain uses automatic reset or a manual reset that holds the fault until a reset button is pressed, and make sure a key switch or password stops unauthorized staff overriding the blanked area. In practice, on a typical press-brake production cell, the integrator teaches the two beams the locating rod occupies, writes the DIP positions onto the setup sheet, then locks the key switch before the shift starts, so the next operator inherits a documented, repeatable configuration rather than a guess.
- ✔ Run a risk assessment first, confirm blanking is permitted for this hazard.
- ✔ Choose the type (fixed, floating, or reduced resolution) from the object’s motion.
- ✔ Teach the minimum number of beams; don’t over-blank “for margin.”
- ✔ Recalculate the safety distance for the new detection capability.
- ✔ Lock the configuration behind a key switch or password, and document it.
Can blanking be changed without re-validating the machine?
No. Any change to the blanked zone change detection capability, which changes the required safety distance and therefore the safeguard’s validity. Treat every blanking change as a re-validation event: recompute the distance, confirm complementary guarding still covers reach-over and reach-under, and re-test the stop function.
Wintriss puts it plainly in its press guidance: adjust blanking as jobs change and “make it part of your setup procedures.” A blanked zone left over from a previous job is one of the quietest ways to compromise a working safeguard.
⚠️ Important
Unmonitored blanking can be defeated. If the curtain does not verify that the blanked object is actually present, an operator can reach through the open zone. Where the standard allows, prefer floating blanking with compulsory object presence, which faults the curtain when the object is missing.
Where Blanking Is Used: Press Feeding, Conveyors, and Fixturing
Blanking earns its keep wherever a known object has to share the protective field with the operator. A common case is an empty pallet entering a cell on a conveyor that feed a hydraulic press: a few lower beams are blanked so the pallet passes, yet the curtain still trips if someone stands on it.
Other common cases are coil stock that rises and fall, clamping hoses that travel with the slide, and robotic fixtures that protrude into the field on every cycle.
A real scenario show why type selection matters. A fabricator running a press brake had a locating rod that protruded through the lower edge of the light curtain on every bend. Fixed blanking failed because the rod shifted a few millimetres between jobs and tripped the curtain; switching to floating blanking of two adjacent beams let the rod travel within its range while keeping the rest of the field live. That fix took minutes once the team stopped treating a moving object as a static one, and it removed roughly a dozen nuisance stop, and the downtime they caused, per shift without weakening protection at the point of operation. On the press itself, the operator still initiates each cycle with palm buttons; blanking never replaces that two-hand control. Where a layout need a whole floor zone protected rather than a flat plane, a safety laser scanner replaces the curtain instead of blanking around the obstacle.
| Application object | Object motion | Blanking type | Key caution |
|---|---|---|---|
| Permanent guard rail or bracket | Stationary | Fixed blanking | Size the curtain to the object width |
| Coil stock rising and falling | Vertical travel | Floating blanking | Limit to 1–2 beams |
| Hydraulic clamp hose | Moves with the slide | Floating blanking | Re-check after a stroke change |
| Empty pallet on a conveyor | Through-feed | Fixed or reduced resolution | Must still trip if a person stands on it |
| Press locating rod | Shifts a few mm between jobs | Floating blanking | Re-teach at every job change |
| Robotic tool entering the field | Cyclic | Reduced resolution | Use object-presence monitoring |
| Sheet stock placed in a press | Loaded by operator | Floating with compulsory presence | Faults if the sheet is absent |
| Varying pallet sizes | Different widths | Floating blanking | Set to the largest expected width |
| Scrap chute or fixed duct | Stationary | Fixed blanking | Recalculate the safe distance |
Application-to-type guidance compiled from IEC/TS 62046 practice and field configuration.
These patterns repeat across packaging, automation, and robotic cells. If you’re matching a curtain to one of them, our guide to press machine safeguarding maps the curtain, blanking, and stop logic to that layout.
5 Field Mistakes That Void Type 4 Blanking
A Type 4 curtain delivers the highest assurance an ESPE can provide, but blanking is a place where good hardware gets undermined by configuration. These five mistakes show up repeatedly in audits and forum threads.
The five most common blanking failures
- Confusing blanking with muting, using a continuous bypass where the application need a timed, sensor-gated one (or vice versa).
- Over-blanking “for margin”floating more beams than the object need, enlarging the blind zone and the safety distance.
- No object-presence monitoringleaving an open tunnel an operator can reach through when the object is absent.
- Not recalculating the safety distancekeeping the old mount after blanking degrades detection capability.
- Undocumented, unlocked changes, a blanked zone left from a previous job, with no key switch and no record.
