PDC sensor for double sheet detection
An ultrasonic double sheet sensor is a through-beam device that determines whether one, two, or no sheets of material are passing between its transmitter and receiver. It is used in printing, paper processing, and packaging to prevent production errors caused by overlapping or missing sheets. This guide explains the operating principles, setup, and applications of double sheet detection sensors.
An ultrasonic double sheet sensor is a specialized device used to detect whether one, two, or no sheets of material are present between its transmitter and receiver. These sensors are critical in industries that process sheets or plates, such as printing, paper converting, label manufacturing, and metalworking. Their primary purpose is to prevent production errors, machine damage, and waste that can occur when sheets overlap (double sheets) or are missing. The sensor operates on a through-beam principle, with a separate transmitter and receiver placed opposite each other. The material to be inspected is passed between them. Ultrasonic double-sheet detectors distinguish between single and double sheets of paper, plastic, or metal foils.
PDC Sensor
The operating principle of a double sheet sensor is based on the attenuation of an ultrasonic signal as it passes through the material. The transmitter generates a high-frequency ultrasonic sound wave, typically at 400 kHz. This wave passes through the material and is received on the other side. The amount of sound that reaches the receiver depends on the number of sheets. With no sheet present, the receiver detects almost 100% of the signal. A single sheet attenuates the signal significantly. If two or more sheets are present, the small air gap between them dampens the signal further. An embedded microprocessor evaluates the sound level at the receiver to trigger one of three outputs: no sheet, single sheet, or double sheet. This allows the system to quickly and reliably identify the state of the material feed.
The setup of a double sheet sensor involves careful positioning and configuration for the specific application. The transmitter and receiver must be accurately aligned, with a recommended mounting distance typically around 40 mm. The sensor often needs a teach-in procedure for the specific material being used. Many sensors are equipped with three inputs for teach-in, allowing the configuration of up to three different settings for different materials or thicknesses. These configurations are often based on the grammage of the material, with standard settings for materials from 20 to 1200 g/m2. For thicker materials like cardboard, a "thick" configuration is used, while a "thin" configuration is for materials under 20 g/m2. The sensors can even be mounted at an inclined angle for thicker plates.
The applications for double sheet sensors are diverse. They are commonly used in printing presses and folding machines to prevent jams and misprints caused by overlapping paper. In the packaging industry, they check for double layers in cardboard or plastic before cutting, forming, or sealing. They are also used in the metal industry to detect double sheets of metal foil before stamping or forming processes. Furthermore, these sensors can be used for ultrasonic splice detection, which senses a splice in high-speed web applications. By detecting these errors early, double sheet sensors save time, reduce waste, and protect expensive machinery from damage. Their reliability is not affected by the flapping of materials, ensuring consistent detection.
The advantages of ultrasonic double sheet detection are significant. They provide a fast and reliable method for monitoring material flow in real-time, which is essential for high-speed production lines. The technology is non-contact and can be used with a wide variety of materials, including paper, plastic, metal, and cardboard. The sensors are robust and can operate in challenging industrial environments. The ability to switch between different configurations during production provides flexibility and ensures optimal detection for various material types. Ultimately, by preventing errors, these sensors contribute to higher product quality, reduced material waste, and improved overall process efficiency.
