{"id":24003,"date":"2026-06-30T08:26:17","date_gmt":"2026-06-30T06:26:17","guid":{"rendered":"https:\/\/roder.it\/inspection\/dimension-and-geometry\/non-contact-speed-and-length-measurement\/"},"modified":"2026-09-30T08:55:32","modified_gmt":"2026-09-30T06:55:32","slug":"non-contact-speed-and-length-measurement","status":"publish","type":"page","link":"https:\/\/roder.it\/en\/inspection\/dimension-and-geometry\/non-contact-speed-and-length-measurement\/","title":{"rendered":"Non-contact speed and length measurement"},"content":{"rendered":"\n

Continuous length measurement<\/strong> concerns materials produced without interruption: strip, wire, cable, tube, profiles, panels and fabrics. In these cases the length is not measured with a fixed rule, but is derived from the speed<\/strong> of the material, integrated over time. It is one of the most important quantities in process control, because it determines cut-to-length, meter counting and the invoicing of the product. Optical speed meters and encoders<\/a> measure it without contact, with high accuracy. <\/p>\n\n

This page belongs to the Dimension and geometry<\/a> section of the Inspection area and examines the physical quantity \u201clength\u201d in the case of moving materials.<\/p>\n\n

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How continuous length is measured<\/h2>\n\n

The principle is simple: if we know the instantaneous speed of the material and integrate it over time, we obtain the distance traveled. The quality of the result therefore depends on the quality of the speed measurement. A measurement affected by slip<\/strong>, such as that of contacting counter wheels, accumulates error meter after meter; a non-contact optical measurement, by contrast, keeps the accuracy constant. As a result, over long lengths the difference between the two methods becomes very significant. <\/p>\n\n

\"Continuous<\/figure>\n\n

The VLM500<\/a> measures speed up to 50 m\/s<\/strong> with an uncertainty below 0.025 %<\/strong> and can totalize lengths up to millions of meters without drift. The VLM60<\/a>, a compact optical encoder, measures down to 0 m\/s and is the direct replacement for measuring wheels. <\/p>\n\n

Accuracy, resolution and repeatability<\/h2>\n\n

Three parameters matter in length measurement. Accuracy<\/strong> indicates how close the measured value is to the real one; resolution<\/strong> is the smallest detectable increment; repeatability<\/strong> is the ability to give the same result in successive measurements. Optical measurement excels in all three aspects: the absence of contact eliminates slip, the encoder output offers fine resolution, and stability over time ensures repeatability. For this reason it is also suited to applications with contractual value, where the declared length must match the real one. <\/p>\n\n

Cut-to-length and meter counting<\/h2>\n\n

Continuous length measurement feeds two key functions directly. Cut-to-length<\/strong> requires knowing the running length precisely in order to command the shear at the exact instant; meter counting<\/strong> documents the production and the length of the rolls or of the pieces. In both cases a length error translates into scrap, into material given away or into disputes with the customer. On a rewinder, for example, the length determines the size of the finished roll. <\/p>\n\n

Advantages of non-contact length measurement<\/h2>\n\n