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Muting Safety Light Curtain
Muting Safety Light Curtain Systems Built for High-Speed Conveyor Lines
The QJKH muting safety light curtains ensure your conveyor is running while keeping your operators safe at any access point. Each unit is shipped with built-in muting sensors and a dedicated safety relay module to be wired in the second you open your packaging or material-handling line.
−10 °C to +55 °C Operating Temp
Cat.4 / SIL 3 Safety Rating
PLe / Type 4 Performance Level
6.0–30.8 ms
Response Time
Up to 70 m
Detection Range
IP65
Protection Rating
Built-in
Relay Module
What Is Muting on a Safety Light Curtain?
Minimizing shutdowns with muting safety light curtains Safeguard safety light curtains maintain the flow of conveyor-fed production lines without endangering workers. In packaging, palletizing and material-handling lines, boxes and pallets are forced through protected openings on the line dozens of times each hour.
At its core, this safety function is an automatic, temporary suspension of the light curtain’s protection — triggered by dedicated muting sensors that distinguish material from personnel. When a series of two or more muting sensors (which are programmed to recognize specific material size and sequence patterns) sense an object, the safety function is disabled for the brief time period required to let the material pass through the aperture. As soon as this object exits the sensing range, complete safety protection is reinstated, to include the full “auto-timed” function, and not once is it ever necessary to deactivate.
A key distinction separates these two functions: blanking permanently masks specific beams for fixed obstructions in the field, while muting temporarily suspends the full protective function based on real-time sensor data. Both serve production efficiency — blanking handles static interference, muting handles dynamic material flow.
QJKH Muting Light Curtain Models & Selection Guide
QJKH ENT-series safety light curtains deliver Cat.4, Type 4, SIL 3, and PLe-rated protection with integrated muting capability when paired with our SRB-2A1B safety relay module. Every unit ships with optical synchronization, IP65 ingress protection, and infrared one-button PNP/NPN configuration — eliminating the mode-mismatch errors that account for a significant share of field commissioning callbacks.
ENT Light Curtain Specifications
10 / 20 / 40 mm
Optical Axis Spacing
14 / 25 / 45 mm
Detection Accuracy
0–70 m (Model E)
Max Detection Distance
6.0–30.8 ms
Response Time
24 V DC ±20%
Operating Voltage
IP65
Protection Class
Detection Distance Selection
Model Code
Detection Range
Typical Application
A
0–10 m
Small press guards, compact workcells
B
0–16 m
Standard conveyor entry/exit points
C
0–5 m
High-speed short-range applications
D
0–40 m
Large palletizing systems, wide openings
E
0–70 m
Warehouse perimeter, extended conveyor runs
SRB-2A1B Safety Relay Module — Muting Interface
Our SRB-2A1B safety relay module connects directly to ENT light curtains through dedicated MUT_H and MUT_L signal inputs. It features safety outputs with 2N/O contacts and 1N/C contact, supports PNP & NPN signal modes by DIP switches while 4 LEDs are used for showing the status such as CH1 (green) for channel 1, CH2 (green) for channel 2, ERROR (red) for errors, and POWER (red) for power supply indication. The whole circuitry supports self testing to lock the output enabling when the two input signals are not matched with one another to prevent the permanent sounds of muting.
How to Select Your Configuration
Match your application in three steps: first, determine detection distance by the physical length of your guard opening. Second, determine the spacing of the optical axis (10 mm for finger detection, 20 mm for hand detection, 40 mm for body detection in accordance with IEC 61496-1). Third, click the box to select the SRB-2A1B relay and muting sensor kit that is right for your conveyor design – T-configuration for bi-directional flow or L-configuration for exit-only systems.
How Muting Works: Sensor Configurations & Safety Logic
A muting system should have at least two muting sensors, a safety controller or muting controller,and a muting lamp that lights when it is unmuted. The sensors are designed to see material moving toward the light curtain, starting the muting cycle on a specific sequence- either a certain part of this sequence is what defines a real pallet rather than a person taking a chance at getting into a dangerous area.
Muting Sensor Configuration Quick-Reference
| Configuration | Sensors | Direction | Key Dimensions (IEC 62046) | Best For |
|---|---|---|---|---|
| T-Configuration (Crossed) | 2 | Bidirectional | d1 < 200 mm, d2 > 250 mm; crosspoint inside danger zone | Conveyor with two-way pallet flow |
| L-Configuration (Parallel) | 2 | Exit only | d5 < 200 mm between AOPD and nearest sensor | Exit-only conveyor openings |
| 4-Beam Parallel | 4 | Bidirectional | d1, d3 < 200 mm; d2 > 250 mm; sequential timing | High-precision palletizing, large irregular loads |
In all cases IEC 62046:2018 specifies a 500 mm diameter matt finished test cylinder must not cause muting to occur – preventing a human from causing the system to mute as a substitute for material. The maximum time to mute is 4 seconds from the time the first muting sensor is un blocked, a fail-safe timer in the safety controller checks this cycle time and faults if this maximum is exceeded.
Proper positioning of the muting sensors relative to the light curtain beam matters more than any other installation variable: the lowest beam of the muting sensor must be at or above the light curtain’s lowermost beam to prevent muting by a foot. The 200mm d1 and d5 dimensions stems from the 95 th percentile human foot length of 285 mm as specified by ISO 15534-3.
“We engineer every ENT muting installation with d5 held under 150 mm (vs IEC 62046 maximum 200 mm) because field data from conveyor retrofits has proven that tighter spacing catches trailing-edge detection failures early, preventing nuisance faults.”
Troubleshooting Common Muting Setup Issues
Donwtime caused by mutes can usually be attributed to no more than five root causes. In fact, field service states that misaligned sensors, caused by a physical hit (forklifts hitting sensor arms, pallets nudging brackets) are responsible for more unscheduled outages than all electrical faults put together.
| Symptom | Root Cause | Solution |
|---|---|---|
| Muting does not activate | Sensor spacing exceeds 200 mm (d5 too large) or material transit time exceeds 4-second window | Verify d5 dimension with a tape measure. Recalculate muting time: T = (material length + margin) ÷ conveyor speed. Adjust sensor position or conveyor speed. |
| Permanent muting condition (safety function stays suspended) | Two muting sensors share a common power feed — a short or open creates a stuck state | Isolate each muting sensor on separate power circuits. SRB-2A1B’s dual-channel self-test detects this condition and locks to ERROR state (red LED). |
| Intermittent false stops (muting activates then immediately faults) | Muting sensor misalignment from physical impact — crosspoint drifts outside danger zone | Install mechanical sensor guards on muting arms. Re-verify crosspoint position (T-config) or parallel beam alignment (L-config). Schedule monthly alignment checks. |
| Muting faults after material clears | ESPE output not cleared within timer window; safety relay contact wear | Check OSSD state on SRB-2A1B (CH1 and CH2 LEDs should turn green). Verify relay lifecycle — SRB rated for 1 million electrical cycles. |
| SRB ERROR LED active on power-up | NPN/PNP mode mismatch between light curtain and relay module | Confirm DIP switch setting on SRB-2A1B matches ENT light curtain output mode. One-button infrared reconfiguration available on ENT receiver. |
SRB-2A1B Status LED Quick Reference
| LED | Color | Meaning |
|---|---|---|
| CH1 |
Green
|
Channel 1 relay energized — normal operation |
| CH2 |
Green
|
Channel 2 relay energized — normal operation |
| ERROR |
Red
|
Fault detected — channel inconsistency, sensor mismatch, or wiring error |
| POWER |
Red
|
Module powered — 24 V DC supply confirmed |
Muting Time Calculator
Calculate whether your conveyor speed and material length fit within the IEC 62046 maximum 4-second muting window.
—
seconds
IEC 62046:2018 maximum muting time: 4.0 seconds
Frequently Asked Questions — Light Curtain With Muting
Blanking permanently masks specific beams for fixed obstructions. Muting temporarily suspends the entire safety function based on real-time sensor input — dynamic, time-limited per IEC 62046.
2 or more through-beam photoelectric muting sensors are correctly aligned, so only an object occupying the entire conveyor opening successfully mutes at the right sequence and window. The 500 mm long matt-finish test cylinder (representing a human torso) must not activate muting- the IEC 62046 requirement shows the sensor system can discriminate material from a person has tried to breach the hazard area.
Three standards form the regulatory backbone. IEC 62046:2018 covers muting system design — sensor configurations, timing requirements, and the 500 mm test cylinder rule. ISO 13849-1:2023 governs the performance level of the muting safety function itself, requiring that the controller’s PL match or exceed the suspended function’s rating. IEC 61496-1:2020 classifies the light curtain hardware into Type 2 and Type 4 categories. One non-negotiable principle ties them together: you cannot use a lower-rated safety controller to mute a higher-rated light curtain, because doing so degrades the overall safety integrity level of the installation.
Four seconds maximum — measured from when the first muting sensor clears. A fail-safe timer enforces the limit and faults the system if exceeded. Calculate your window: (material length + margin) ÷ conveyor speed.
Yes. Operating muting from PLC outputs will compromise the safety score for the entire installation. Muting sensors need to feed into a certified safety PLC, safety relay (such as the SRB-2A1B), or safety controller with input rated to the performance level demanded by the system. This is a required part of functional safety under ISO 13849-1.
ENT-series light curtains generate dual PNP or NPN safety outputs, compatible with all leading safety PLCs including Allen-Bradley GuardLogix, Siemens F-CPU, Omron NX-SL. Industry-standard 24 VDC 20% operating power supply input, and M12 connector wiring interface exist. Additionally, the SRB-2A1B relay provides an alternative safety wiring route in installations where a safety PLC is not used.
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