Fixed blanking on a safety light curtain permanently masks a defined group of adjacent beams so a stationary fixture, conveyor, or worktable can sit inside the protection field without stopping the machine, while every remaining beam continues to detect an operator [S1][S2]. The masked zone is taught once, then the OSSD outputs behave as if those beams were simply absent from the array.
That is fundamentally different from floating blanking, which only allows one or more beams to be temporarily masked, and from muting, which is a timed, sequence-dependent override used for material flow rather than a fixed obstruction [S1][S3]. For permanent fixtures such as a pallet locator, a column inside a robotic cell, or a bracket that physically cannot move, fixed blanking is the feature the safety plan is calling out.
What fixed blanking actually does to the beam array
Fixed blanking allows a fixed portion of the protection field (a fixed set of beams) to be occupied, while all the other beams operate normally [S1]. On a Type 4 / SIL3 / PLe array the device still self-tests each scan cycle, and the masked beams are simply removed from the safety evaluation; a fault inside the masked zone is not ignored, it is treated as a configuration that must not change [S3].
SmartScan describes the same behaviour as deselecting a fixed area of beams in the light curtain's sensing field, which is typically used when stationary objects, fixtures, tables, etc. are permanently obstructing a portion of the sensing field [S2]. Pilz is more restrictive in its wording: with fixed blanking, a fixed zone of the light curtain is switched off and the object or item cannot move within the danger zone [S3]. The SICK knowledge base confirms the same two-mode taxonomy, fixed or floating, and adds the standard guard against ever using blanking to bypass a real guarding need [S4].
The teach sequence is consistent across vendors: power off, place the physical obstruction in the sensing region, power on with the device in Learn mode, let the receiver lock the beam pattern once all LEDs are steady, then exit Learn mode with a key or PIN so the configuration cannot be altered by an operator on shift [S2][S3]. SICK also calls out the historical point: the technology goes back to a 1951 patent by Erwin Sick, so fixed blanking is not a recent marketing feature, it is a decades-old capability on most safety light curtains [S4].
Why EN ISO 13855 still controls the safety distance
EN ISO 13855 (the harmonised standard for positioning safeguards with an electro-sensitive protective equipment response) is the document SICK's own engineering guidance points to for sizing the light curtain and the safety distance to the hazard, and blanking changes that calculation [S4]. With blanking active, the effective detection capability of the array drops in the masked zone: if a 30 mm finger-resolution curtain has three beams masked, a 90 mm aperture is created in that part of the field, and the risk assessment has to be reconciled with the machine's reach and stop time [S4][S5].
The SICK post explicitly warns that the protection chosen is driven by what is being guarded, point of operation, access, perimeter, or area, and that the protective field height has to be selected accordingly, with EN ISO 13855 as the positioning reference [S4]. Fixed blanking cannot be used to retrofit a shorter curtain into a wider hazard; the safety distance calculation runs from the nearest effective beam to the hazard, and the masked beams do not count toward that distance [S1][S4].
On the selection side, the DigiKey machine-safety selection guide lines up the criteria that matter when blanking is on the spec sheet: detection capability, protective height, number of beams, beam pitch, operating range, and IP rating (commonly IP65 for washdown cells, IP67 where coolant and chips are heavy) [S5]. The guide also notes that an NPN or PNP output is set high or low when a beam is broken, so the muted zone must be visible to the controller as a non-firing region, not a re-mapped output [S5].
Fixed versus floating versus muting: the comparison that matters
Three override behaviours show up on every modern light curtain datasheet, and they are not interchangeable. Fixed blanking is permanent, the masked zone is set at commissioning, and the obstruction is not allowed to move [S1][S3]. Floating blanking is dynamic: one or two beams may be interrupted at any time for the OSSD to stay high, which is the right tool for small, slow-moving objects such as a hanging cable or a fixtured part moving slightly on a conveyor [S1]. Muting is a timed, sequenced override triggered by the machine's own logic, used when a pallet or tote is allowed to enter the field during a known safe part of the cycle, and it must be re-validated for each new line layout [S3].
In side-by-side selection terms, fixed blanking suits a stationary fixture such as a column or worktable inside a robotic cell, floating blanking suits a moving part whose position varies, and muting suits material-handling in/out of the field. Picking the wrong one is a common audit finding: a permanently installed bracket should never ride on a floating-blanking configuration, because the floating tolerance is designed to allow a one- or two-beam transient, not a 200 mm structural column. For machines that share guarding hardware with multiple SKUs, the device's Learn mode and PIN-locked configuration are what keep a well-meaning operator from re-teaching the array into an unsafe state on a Saturday [S2][S3].
Commissioning and re-validation rules that are non-negotiable
Wintriss's safety light curtain guidelines state that fixed blanking can be accomplished by placing a physical object called a blanking window over the face of the light curtain receiver, but in practice on a modern Type 4 device the masking is done in firmware via the device's configuration menus, with the physical obstruction placed in the field for the learn cycle [S6]. Either way, the procedure requires the same validation: the OSSD must be forced OFF when the masked zone is removed, and the change must be authorised by a competent person rather than left to the operator on duty [S1][S6].
AutomationDirect's 2011 guidance, still cited because the safety rules have not changed, defines fixed blanking as when a fixed set of adjacent light beams is set to be permanently inactive to allow product or part of the process to enter [S7]. The wording matters: "permanently inactive" is the legal term that ties fixed blanking to a documented change request, not to a tool change. Datalogic's quick-start video shows a UI detail that vendors implement in different ways: tolerance arrows at the top or bottom of the masked zone, controlling which end of the array re-zeros the learn reference [S8].
Two re-validation rules follow from the same source set. First, every time a fixture is moved, added, or removed inside a fixed-blanked zone, the light curtain must be re-taught and the new configuration documented, because the device's safety case is built on the assumption that the masked zone is exactly what was originally learned [S1][S2]. Second, the configuration must be protected against operator access, typically a key switch or PIN code on the receiver or the safety controller, so the override cannot be disabled without a deliberate, recorded action [S3].
What the feature is for, and what it is not for
Fixed blanking is for a permanent obstruction: a structural column, a tooling bracket, a section of conveyor that physically passes through the protection field, or a fixed backstop on a press [S1][S2][S3]. It is not for moving product, it is not for access during a normal cycle, and it is not a substitute for a properly sized curtain in the first place. Pilz's lexicon wording is deliberately strict on this point: with fixed blanking the object cannot move, full stop [S3].
It is also not the right feature when a different risk-reduction measure would work. If the hazard is simply that a beam is in the way, the first move is to reposition the curtain, raise it on stands, or use a mirror column to redirect the beam path, which leaves the entire array at full detection capability. The role fixed blanking plays on a real line is the one that has no other option: a fixture is bolted in, the beam geometry is fixed, and the safety case has to absorb the masked zone. Used that way, with the change-control discipline above, fixed blanking lets the line run without forcing the engineer to oversize the array or re-locate an entire machine.
For a specifier weighing a blanked Type 4 array against a hard guard, the practical decision tree is short. If the obstruction is permanent and small relative to the field height (under roughly 20% of the beams), fixed blanking on a Type 4 / PLe / SIL3 device is usually the lower-cost, lower-footprint answer. If the obstruction is larger, or its boundary will change as products change, the answer is a hard guard, a movable interlocked guard, or a safety laser scanner with a configured warning and detection field instead of a masked light curtain. Related guidance on adjacent machine-safety topics, including interlock switch selection, sits in the guard locking vs non-locking interlock comparison.
Trackable signals for the next planning cycle
Three signals are worth watching on a quarterly cadence. First, EN ISO 13855's revision status and any new wording on masked-zone sizing, since that drives safety-distance calculations for every Type 4 array in the field. Second, vendor-by-vendor changes to the learn interface (PC tool, app, or HMI), because each generation lowers the chance of an operator re-teaching the array on shift and tightening the change-control loop. Third, the audit record on fixed-blanked cells during ANSI B11.19 / EN ISO 13849 reviews, where the recurring finding is still the same one Pilz flags: a masked zone that was once small has grown, fixture by fixture, until the effective detection capability no longer matches the risk assessment. [S4]
For the relevant spec sheets and selection criteria, see fixed gas detector, and glass curtain wall.