[Core Summary]
The through-beam photoelectric sensor consists of an independently placed emitter and receiver. When an object blocks the light beam between them, it triggers the sensor. Among the three types of photoelectric detection (through-beam, diffuse reflection, and specular reflection), it has the longest detection distance and the strongest resistance to background interference, making it suitable for long-distance and high-interference scenarios. Common confusions surrounding this term include: the applicable boundaries of the three working modes, the relationship between detection distance and light spot, and the power supply and output form of long-distance systems. This entry uses Telco (Telco Sensors, Denmark) SM 3000 and PA 01 as references to explain each item.
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Definition and Working Principle
Through-beam technology separates the light source from the receiver: the emitter continuously emits light, while the receiver detects whether it receives the light. When an object enters the optical path between the two and blocks the light beam, the output of the receiver flips. Because the light path "passes through once" between the emitter and receiver, it is not affected by the color, material, or reflectivity of the object's surface, and black rubber and transparent film can also be detected stably.
Comparison of Three Working Modes
Correlation Type: Longer distance and more stable operation, but requires wiring on both sides for installation. Diffuse Reflection Type: Integrated transmitter and receiver, triggered by reflected light from an object, easy to install but limited distance, greatly affected by color and surface. Mirror Reflection Type: Integrated transmitter and receiver, with a mirror placed opposite, distance falls between the two. The SM 3000 Correlation Type has a detection range of 1–15 m, suitable for production lines, logistics sorting, and large equipment; when longer distances or centralized control at multiple points are required, the PA 01 Long-Range Photoelectric System can achieve a correlation range of 0–45 m.
Detection distance and optical path alignment
The nominal distance of the through-beam type is given under clean air and well-aligned conditions. For the SM 3000 through-beam type, the range is 1–15 m, and for the PA 01 through-beam type, it is 0–45 m. The actual usable distance may be reduced due to dust, mist, and alignment errors. For long-distance installations, it is essential to use rigid supports and laser alignment, and to reserve power margin for post-pollution scenarios. When detecting transparent objects, minor adjustments can be made to the optical path or a model with polarization can be selected to suppress interference from specular reflection.
Power supply and output form
SM 3000 is a DC node powered by 10–30 V DC, featuring a three-wire NPN or PNP transistor output, suitable for standard industrial PLCs. The PA 01 remote optoelectronic system is designed for longer distances and existing AC power supply scenarios, supporting 230 V AC, 115 V AC, or 24 V AC/DC, with an output of either one relay or one transistor, connected via an 11-pin DIN socket, making it ideal for retrofitting old production lines or centralized layout in control cabinets. Both models offer cable or plug connections, allowing for customization according to needs.
Summary of Selection Key Points
First, determine the working mode based on the detection distance and on-site environment: for long distances and strong interference, choose through-beam; for short distances and limited installation space, choose diffuse reflection or mirror reflection. Then, confirm the power supply system (DC or AC) and output type (NPN/PNP/relay) to match the controller. Finally, verify the protection and certification - both SM 3000 and PA 01 can be optionally certified for ATEX explosion-proof and UL325, and for explosion-proof or gated scenarios, confirm the model and delivery date in advance.
[Parameters Table]
**Parameter Source Description**: The measurement range, power supply, and output are sourced from the Telco Sensors SM 3000 and PA 01 product catalogs. The response frequency, spot size, and ambient temperature range for specific models are subject to the latest manufacturer's catalog. If necessary, please verify.
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