What Is the Wiring Rule for 4-wire Through-beam Photoelectric Sensors?

The through-beam type features a transmitter emitting red or infrared light and a receiver capturing the light signal. A signal will be triggered once a passing object blocks the light path. This sensor typically has four lead wires: the transmitter only connects the brown (positive power) and blue (negative power) wires; the receiver additionally uses the black wire as the signal output line besides the brown and blue power wires.

Common Applications of Photoelectric Sensors

1. Smoke Turbidity Monitor Industrial smoke emission monitoring is a core part of environmental pollution control. Real-time measurement, automatic data display and over-limit alarm are required to track smoke discharge volume. Flue gas turbidity is judged by light attenuation during transmission inside flues. Higher turbidity means more light is absorbed and scattered by smoke particles, less light reaches the photodetector, and the output signal strength directly reflects turbidity changes.

2. Photocell for Detection & Automatic Control Photocells share a similar working principle with photodiodes for photoelectric detection, with distinct structural design and manufacturing processes. Requiring no external driving voltage, they feature high conversion efficiency, wide spectral coverage, stable frequency response and low noise. They are widely adopted in photoelectric reading, optocoupling, grating distance measurement, laser alignment, film sound playback, ultraviolet monitoring and flameout protection for gas turbines.

Core Advantages of Photoelectric Sensors

① Long detection distance: Through-beam models support a detection range over 10 m, outperforming magnetic and ultrasonic sensors for long-distance detection scenarios.

② Broad object adaptability: Detection relies on light blockage rather than material conductivity, so it works for glass, plastic, wood, liquid and nearly all objects, not limited to metals like proximity sensors.

③ Fast response speed: Light travels at extreme speed with fully electronic internal circuits, no mechanical action delay for rapid signal feedback.

④ High resolution: Optimized beam focusing and customized optical receiving systems enable tiny object detection and high-precision positioning tasks.

⑤ Non-contact detection: No physical contact with targets prevents scratches on tested objects and sensor wear, extending service life.

⑥ Color recognition capability: Different colors produce unique light reflectivity and absorptivity under fixed wavelengths, which can be leveraged for color sorting and identification.

⑦ Easy alignment adjustment: Visible light emitters let users directly observe the beam path for quick position calibration.

Working Principle of Through-beam Photoelectric Sensors

Basic Composition Photoelectric switches convert light intensity fluctuations into electrical signals for control. A standard unit consists of a transmitter, a receiver and a detection circuit. The transmitter emits continuous or pulse-modulated light from LED/laser diode sources. The receiver is built with photodiodes or phototransistors, fitted with lenses and aperture filters upfront, followed by a detection circuit to filter and process valid signals. Auxiliary parts include triangular reflectors and optical fibers. Triangular reflectors made of micro pyramid materials reflect light back along the original axis within a 0–25° angle deviation for stable signal transmission. Optical fibers expand application boundaries for embedded transceivers, supporting tiny object detection under high-temperature or space-restricted industrial conditions.

Through-beam Switch Mechanism Separating the transmitter and receiver greatly extends detection range. A standalone pair of emitter and receiver forms a through-beam photoelectric switch, with a measurable distance from several meters up to dozens of meters. The two units are mounted on opposite sides of the target passing path; when an object blocks the light path, the receiver activates and outputs a switching control signal.