PDC sensor for label detection
An ultrasonic label sensor is a fork-shaped device used to reliably detect labels on a backing material at high speeds. It distinguishes between the label and the backing material by sensing differences in ultrasonic signal attenuation, making it ideal for transparent, reflective, or metallized labels. This guide covers the operating principles, setup, and applications of ultrasonic label sensors.
An ultrasonic label sensor is a specialized device used in labeling machines to detect the presence and position of labels on a continuous web of backing material. The primary challenge in label detection is distinguishing the label from the carrier, especially with transparent, reflective, or metallized materials where optical sensors often fail. Ultrasonic sensors overcome this by using sound waves, which are not affected by the color or reflectivity of the material. The sensor is typically a fork sensor, where the label web passes through the fork. The transmitter is located in one leg of the fork, and the receiver in the other. The sensor can reliably detect high-transparency, reflective and metallised labels without contact, regardless of colour.
PDC Sensor
The operating principle is based on the attenuation of ultrasonic sound waves. A high-frequency ultrasonic transmitter in one leg of the fork beams a fast sequence of pulses through the backing material. The sound pulses cause the backing material and the label to vibrate, creating a greatly attenuated sound wave on the opposite side. The receiver in the upper leg detects this wave. Because the label and the backing material have different acoustic properties, they transmit different signal levels. The sensor evaluates this signal difference to distinguish between the backing material and the label. This method is highly effective even when labels are closely spaced on the web.
Ultrasonic label sensors are designed for high-speed applications and offer fast response times. For example, the esf-1 sensor from microsonic has a response time of less than 300 µs, enabling its use at very high web speeds. The sensor features teach-in methods to adapt to different label and backing material combinations. These methods can include learning both the backing material and the label dynamically. Some sensors feature IO-Link connectivity for parameterization and integration into modern industrial networks. The measurement cycle time automatically self-adjusts to the sound power required. The sensors are also compact, with slot widths as small as 3 mm and slot depths of 69 mm, allowing them to be placed close to the labeling arm.
The primary application for ultrasonic label sensors is in labeling machines. They ensure that labels are dispensed precisely at the correct position on a product. The sensor detects the gap between labels on the backing web and triggers the labeling mechanism. This is essential for high-speed production lines, where accurate and consistent label placement is critical. They are used in industries ranging from food and beverage to pharmaceuticals and logistics. The sensors are particularly valued for their ability to detect metallized, transparent, and paper labels with 1 mm gap accuracy and support production speeds up to 240 m/min. They can also detect labels on a splice to ensure continuity of the labeling process.
The benefits of using ultrasonic label detection are clear. They provide a reliable detection method that is not fooled by the optical properties of the label or backing material, which is a common issue with photoelectric sensors. This leads to higher accuracy and fewer missed labels, reducing waste and rework. The fast response time allows for high-speed production without sacrificing precision. The sensors are also robust and require minimal maintenance. Features like IO-Link enable easy setup and diagnostics, providing real-time quality monitoring. Overall, ultrasonic label sensors are a key component in modern, high-efficiency packaging and labeling operations, ensuring product quality and maximizing throughput.
