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Safety Light Curtain: Key Components and Functions of Industrial Safety Protection
Jul 24,2025
A safety light curtain is a photoelectric sensor used for industrial safety protection. It forms a protective area by emitting and receiving infrared beams. When the beam is blocked, it triggers a safety signal to prevent personnel or objects from entering the dangerous area. Its internal structure can be divided into several core components, and each part works together to achieve the safety protection function.
01
Core functional components
Safety light curtains are usually divided into a transmitter and a receiver, which are used in pairs. They have similar internal structures but different functions.
1. Light source module
• Composition: Consists of multiple infrared light-emitting diodes (LEDs), usually using infrared light with a wavelength of 850nm-940nm (invisible to the human eye to avoid interfering with operations).
• Function: The LED array in the transmitter is arranged at a certain interval (such as 10mm, 20mm, 40mm, etc.) to emit parallel or converging infrared beams to form a dense light grid.
• Features: The LED needs to be modulated (such as a pulse signal of a specific frequency) to reduce the interference of external light (such as sunlight, lighting).
2. Optical lens / lens group
• Composition: Each LED (transmitter) and photoelectric receiving element (receiver) corresponds to a small convex lens or cylindrical lens.
• Function:
◦ Transmitter: Focuses the scattered light emitted by the LED into a parallel beam to ensure that the beam remains concentrated over a long distance (such as 1m-30m) and reduces attenuation.
◦ Receiver: Focuses the received infrared beam onto the photoelectric receiving element to improve sensing sensitivity.
• Features: The lens material is mostly optical plastic or glass, which must be resistant to temperature and impact (to adapt to the industrial environment).
3. Photoelectric receiving module
• Composition: The receiver is installed with multiple photodiodes (PD) or phototransistors corresponding to the position of the transmitter LED to form a receiving array.
• Function: Receive infrared light beam and convert the optical signal into an electrical signal (current / voltage change), and transmit it to the signal processing circuit.
• Features: It needs to match the LED wavelength of the transmitter and have a high response speed (to adapt to rapid occlusion detection).
4. Signal processing circuit
• Composition: Including amplification circuit, filter circuit, demodulation circuit, logic judgment circuit, etc. (mostly integrated in dedicated chips).
• Function:
◦ Amplification: Amplify the weak electrical signal output by the receiving module to facilitate subsequent processing.
◦ Filtering / Demodulation: Filter external stray light interference and extract the effective signal consistent with the modulation frequency of the transmitter.
◦ Logic judgment: Detect whether the light beam is blocked (single or multiple). If it meets the trigger conditions (such as the blocking exceeds the preset time), a safety signal is output.
5. Control and output module
• Composition: Including relays, transistors (such as PNP/NPN), safety relay modules (in accordance with safety standards, such as SIL3, PLe), etc.
• Function:
◦ Receive the judgment result of the signal processing circuit and output a control signal (such as disconnecting the power of dangerous equipment and triggering an alarm).
◦ Supports multiple output methods: such as safety contacts (normally closed / normally open), analog output (some high-end models), communication interface (such as RS485, used to connect to PLC).
• Features: It must meet safety certification requirements (such as EN 61496 standard) to ensure the reliability of the output signal (such as dual-circuit design to prevent single-point failures).
6. Power module
• Composition: Including rectifier circuit, voltage regulator circuit (such as linear regulator, switching power supply chip).
• Function: Convert the external input power supply (such as DC 24V industrial power supply) into a stable voltage (such as 5V, 3.3V) required by each module inside the light curtain to ensure stable circuit operation.
• Features: It has over-voltage and over-current protection functions to adapt to the fluctuations of industrial power supplies (such as 18V-30V wide voltage input).
02
Auxiliary structural components
1. Housing and protection structure
• Composition: Metal (such as aluminum alloy) or high-strength plastic shell, the surface may be covered with a scratch-resistant panel (such as polycarbonate PC board).
• Function: Protect the internal circuit and optical components from dust, oil, and mechanical collision. The protection level is usually IP65/IP67 (suitable for humid and dusty environments).
2. Installation and calibration parts
• Composition: Mounting holes and positioning slots on the housing, some models have built-in fine-tuning knobs or LED indicators (for alignment and calibration).
• Function: Ensure that the beams of the transmitter and receiver are accurately aligned (misalignment can cause false triggers), and the indicator light can display the working status (such as power, beam alignment, fault alarm).
3. Auxiliary function modules (high-end models)
• Self-diagnosis circuit: Detects whether internal components (such as LED, PD, power supply) are faulty and outputs a fault signal (in accordance with safety integrity requirements).
• Blind zone setting function: Through software or hardware settings, ignore the occlusion of specific areas (such as a small area that allows tools to pass through).
• Temperature compensation circuit: Stabilizes LED light intensity and receiving sensitivity in high and low temperature environments (such as -10℃-55℃).
The core of a safety light curtain is to form a protective barrier through an array of "emission-reception" light beams. Its internal structure is designed around "precise light emission, stable reception, anti-interference processing, and reliable output." Each component works together to achieve fast (response time typically <20ms) and safe (compliant with international safety standards) protection functions. The differences between different models (such as small-sized hand protection and large-sized body protection) are mainly reflected in the beam spacing, protection height, detection distance, and additional functions, but their basic structure remains the same.
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