PDC Sensor for Label Detection - Ultrasonic Fork Sensor Technology for Reliable Label Sensing on Transparent and Reflective Materials
This in-depth technical article examines the application of PDC sensors for label detection, covering the ultrasonic fork sensor architecture, the signal difference evaluation between backing material and label, the teach-in methods for different label types, and the integration with high-speed labeling machines for precise label positioning and counting.
Ultrasonic label detection sensors are specialized fork sensors designed to reliably detect labels on a backing material in high-speed labeling machines. The sensor operates by guiding labels through a fork-shaped housing, where an ultrasonic transmitter in the lower leg beams a fast sequence of pulses through the backing material. The sound pulses cause the backing material to vibrate, generating a greatly attenuated sound wave on the opposite side, which is received by the receiver in the upper leg of the fork. The backing material transmits a different signal level from the label, and this signal difference is evaluated by the sensor. The sensor can reliably detect high-transparency, reflective materials, metallised labels, and labels of any colour. The measurement cycle time automatically self-adjusts to the sound power required, optimizing performance for different label and backing material combinations. The sensor's response time is less than 300 µs, enabling use at high web speeds, making it suitable for high-speed labeling applications.
PDC Sensor
The signal difference evaluation between the backing material and the label is the core of the label detection principle. The backing material and the label have different acoustic properties, causing them to transmit different signal levels through the ultrasonic fork. The signal difference between the backing material and the label can be very slight, requiring the sensor to learn the label for reliable distinction. The sensor uses a piezoceramic transmitter and receiver to generate and detect the ultrasonic signal. The attenuation results from the different material thicknesses of the base material with label and the bare base material. Unlike optical sensors, the ultrasonic fork sensor relies on damping—a process where the thickness of a material determines the degree to which the sensor absorbs sound waves. This makes the sensor ideally suited for detecting labels on any label material regardless of color, transparency, or surface finish, providing reliable detection where optical sensors would fail.
The teach-in methods for different label types enable the sensor to adapt to various label and backing material combinations. The sensor provides three different teach-in methods. Method A learns both backing material and label dynamically: the backing material and its labels are guided through the fork at a constant speed, and the sensor automatically learns the signal level for the labels and for the gaps between them. Method B performs separate teach-in for backing material and labels: when the signal difference is very slight, the sensor teaches the backing material and the label separately, with the switching threshold then lying between these two signal levels. Method C learns web material only: for splice detection, only the sheeting is learned, and the sensor detects the level difference at the splice. The teach-in procedure can be carried out with the button on the top of the housing or with pin 5 on the connector, providing flexibility for different installation scenarios.
The integration with high-speed labeling machines enables precise label positioning and counting. The sensor's fast response time (< 300 µs) ensures accurate detection even at high web speeds. The sensor provides two switching outputs for label/splice detection and web break monitoring, enabling comprehensive control of the labeling process. The sensor's IO-Link interface supports the new industry standard, providing bidirectional communication for remote configuration, diagnostics, and data logging. The Smart Sensor Profile enables more transparency between IO-Link devices, and the Smart Sonic Function supports recipe management via IO-Link. The sensor's ability to detect labels regardless of printed design, transparency, or surface characteristics makes it suitable for a wide range of labeling applications, from food and beverage to pharmaceuticals and logistics.
The future of ultrasonic label detection is moving toward higher integration and intelligence. The development of sensors with IO-Link communication is enabling advanced diagnostic capabilities, including signal quality monitoring and predictive maintenance. The integration of machine learning is being explored to automatically optimize the teach-in parameters for different label and backing material combinations, reducing setup time and improving detection reliability. The use of higher frequencies and advanced signal processing is improving the ability to detect labels with very small signal differences, such as thin labels on similar backing materials. The ultrasonic label sensor remains an essential component in modern labeling machines, providing reliable, non-contact label detection for efficient, high-quality packaging operations.
