Laser light diameter gauges are non-contact systems dedicated to the continuous measurement of the diameter of moving cylindrical products such as wires, cables, tubes, profiles, bars and extruded products. They use a collimated laser beam that passes across the product, casting a shadow on a linear CCD/CMOS sensor: the size of the shadow corresponds directly to the diameter. Multi-axis configurations (2 or 3 measuring planes) provide simultaneous measurement of minimum, maximum and mean diameters and of ovality, enabling 100% dimensional control in the production line with acquisition rates up to hundreds of Hz.
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Measuring principle
The shadow measuring principle uses a laser emitter with collimating optics that generates a parallel beam wider than the maximum diameter of the product. The product, positioned at the center of the beam, intercepts the light and creates a shadow which, collected by a receiving lens, is focused onto a digital linear sensor. A subpixel edge-detection algorithm determines the exact position of the edges of the shadow, from which the diameter is obtained with resolution down to 0.1 μm. Multi-axis systems use heads set at 60°, 90° or 120° to cover the whole circumference.
Features
Industrial laser diameter gauges cover measuring ranges from a few mm (0.03-2 mm for fine wires) up to 250-500 mm and beyond (large tubes and profiles). Typical accuracy is ±0.1-1 μm on fine wires and ±10-50 μm on medium-sized products. The acquisition rate reaches 500-3000 Hz, allowing measurement on products at extrusion speeds up to 200-300 m/min. Digital interfaces (Profinet, EtherCAT, Modbus, OPC UA) enable real-time integration with process control systems for automatic adjustment.
Applications
Laser diameter systems are used in drawing lines for metal wire (copper, steel, aluminum), in the production of electrical, optical and telecommunication cables (checking the diameter of the conductor, the sheath and the insulation at every stage), in the extrusion of plastic tubes and profiles (PE, PVC, PP, ABS) and rubber ones (flexible hoses, seals), in the rolling of wire rod and bars, and in the production of welding wire, synthetic textile yarn and drawn metal profiles. Continuous dimensional control reduces scrap and allows raw material consumption to be optimized.
Integration and functions
The most advanced systems include statistical calculation functions (mean, standard deviation, Cp/Cpk capability), tracking of the position along the product (with an external encoder), out-of-tolerance alarms, automatic line control (feedback on speed, temperature and extrusion pressure), automatic batch reporting and data archiving for traceability. The mechanical structure of the measuring head is designed for harsh environments (dust, vapors, vibration) with an IP65 protection rating and devices for automatic cleaning of the optical window.
Selection criteria
Selecting a laser diameter gauge depends on the nominal measuring range of the product, on the accuracy required (according to the tolerances), on the number of axes needed (1 for a simple diameter, 2-3 for ovality), on the speed of the product, on the ambient conditions and on the need for integration with the line control system. Performance is verified with cylindrical standards certified to ISO 17025 and with Gage R&R trials on the real product.
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