Photoelectric switches are fundamental components in modern industrial automation, offering non-contact detection of objects. Among the diverse models available, the GD18-S, GV18-S, and their variants with specifications like 73 and 120 represent a popular and reliable series. These devices are engineered for precision, durability, and adaptability in challenging environments. This guide delves into their technology, key differences, applications, and selection criteria to provide a thorough understanding for engineers and procurement specialists.
The core technology behind these switches is based on the photoelectric principle. They typically consist of an emitter (light source) and a receiver. The emitter projects a light beam—often infrared, red, or laser—toward the receiver. An object interrupting or reflecting this beam triggers a change in the receiver's output state. The GD18-S and GV18-S series commonly utilize this principle in different sensing modes: through-beam, retro-reflective, and diffuse-reflective. The "S" suffix often denotes a particular housing style, sensing distance, or output configuration, while numerical codes like "73" and "120" frequently refer to critical specifications such as sensing range (e.g., 73mm or 120mm) or housing thread size (e.g., M18).
A primary distinction lies in their form factor and sensing capabilities. Models designated with a sensing range like 73 or 120 indicate the effective operating distance. A "73" model might be optimized for close-range, high-precision detection, while a "120" model offers a longer reach for applications requiring more standoff. The GD18-S and GV18-S may differ in their housing material, ingress protection (IP) rating, or light source type. For instance, one might feature a robust metal housing for heavy-duty applications, while another uses a chemical-resistant plastic. The output type is another critical differentiator; these switches commonly provide NPN (sinking) or PNP (sourcing) transistor outputs, or relay contacts, to interface seamlessly with PLCs (Programmable Logic Controllers) and other control systems.
The application spectrum for these photoelectric sensors is vast. In packaging machinery, they accurately detect the presence of boxes or products on a conveyor, ensuring proper filling and sealing. Within automotive assembly lines, they verify the correct positioning of components for robotic arms. The food and beverage industry relies on their sanitary designs for bottle cap detection or liquid level sensing. Their robust construction makes them suitable for harsh environments with dust, moisture, or vibration, such as in material handling or woodworking. The specific choice between a GD18-S with a 73mm range and a GV18-S with a 120mm range depends entirely on the physical constraints and detection requirements of the installation site.
Selecting the correct photoelectric switch requires careful consideration of several parameters. First, define the sensing distance needed and the size/type of the target object. Small, dark, or transparent objects may require a specialized sensor with a focused beam. Second, assess the environmental conditions, including temperature extremes, potential for washdowns (requiring high IP ratings like IP67 or IP69K), and exposure to dust or oils. Third, the electrical characteristics must match the control system: operating voltage (commonly 10-30V DC or 90-250V AC), output type (NPN/PNP/Relay), and connection method (pre-wired cable or connector). Finally, consider mechanical factors like the housing size (the "18" often refers to an 18mm diameter barrel) and mounting style (threaded, bracket, or flush). Consulting the manufacturer's datasheet for the exact GD18-S/GV18-S/73/120 model is essential to confirm all specifications.
Installation and alignment are crucial for reliable operation. For through-beam sensors, precise alignment of the separate emitter and receiver units is necessary. Retro-reflective models require a correctly positioned reflector. Diffuse sensors need to be angled appropriately to avoid false triggers from background objects. Most modern sensors feature a visible LED beam or an alignment indicator to simplify setup. Regular maintenance involves keeping the lens clean from dirt and debris and periodically checking the mechanical stability of the mount and the integrity of electrical connections.
In conclusion, the GD18-S, GV18-S, 73, and 120 photoelectric switches form a versatile family of sensors crucial for automation. Understanding their technological basis, model variations, and application-specific requirements enables optimal selection and deployment. By paying close attention to sensing range, environmental ratings, output configuration, and installation practices, users can ensure long-term, reliable object detection that enhances efficiency and safety in automated systems. Their role in enabling precise, non-contact sensing continues to be indispensable across countless industries.
