{"id":24179,"date":"2026-05-13T15:43:35","date_gmt":"2026-05-13T13:43:35","guid":{"rendered":"https:\/\/roder.it\/inspection\/rotation-speed-and-linear-motion\/non-contact-linear-speed-measurement\/"},"modified":"2026-09-30T14:30:12","modified_gmt":"2026-09-30T12:30:12","slug":"non-contact-linear-speed-measurement","status":"publish","type":"page","link":"https:\/\/roder.it\/en\/inspection\/rotation-speed-and-linear-motion\/non-contact-linear-speed-measurement\/","title":{"rendered":"Non-contact linear speed measurement"},"content":{"rendered":"<p class=\"wp-block-paragraph\">Non-contact laser linear speed meters (Velocity Length Meter, VLM) are high-precision industrial instruments for the non-contact measurement of the linear speed and total length of moving products. They use laser Doppler or image cross-correlation principles to measure product speed non-invasively, with accuracies typically of the order of 0.05% of the reading. They replace measuring-wheel systems in applications where physical contact is not wanted because of wear, contamination, product temperature or the precision required.  <\/p>\n<div style=\"height:30px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n<div class=\"wp-block-cover is-light popmake-11245\" style=\"border-width:1px;border-top-left-radius:10px;border-top-right-radius:10px;border-bottom-left-radius:10px;border-bottom-right-radius:10px;min-height:250px;aspect-ratio:unset;\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"213\" class=\"wp-block-cover__image-background wp-image-14896 size-large\" alt=\"banner aiuto nella scelta dello strumento oppure della tecnologia\" src=\"https:\/\/roder.it\/wp-content\/uploads\/2026\/06\/banner_technical_support_choose_products-1024x213.png\" data-object-fit=\"cover\" srcset=\"https:\/\/roder.it\/wp-content\/uploads\/2026\/06\/banner_technical_support_choose_products-1024x213.png 1024w, https:\/\/roder.it\/wp-content\/uploads\/2026\/06\/banner_technical_support_choose_products-300x63.png 300w, https:\/\/roder.it\/wp-content\/uploads\/2026\/06\/banner_technical_support_choose_products-768x160.png 768w, https:\/\/roder.it\/wp-content\/uploads\/2026\/06\/banner_technical_support_choose_products.png 1200w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><span aria-hidden=\"true\" class=\"wp-block-cover__background has-background-dim\" style=\"background-color:#d3d6dc\"><\/span><div class=\"wp-block-cover__inner-container is-layout-constrained wp-container-core-cover-is-layout-a304f9a9 wp-block-cover-is-layout-constrained\">\n<p class=\"has-text-align-right has-ti-fg-color has-text-color has-link-color wp-elements-1 wp-block-paragraph\" style=\"font-size:clamp(21.536px, 1.346rem + ((1vw - 3.2px) * 1.726), 35px);\"><strong>Would you like help choosing the right product ?<\/strong><\/p>\n\n\n\n<div class=\"wp-block-buttons is-content-justification-right is-layout-flex wp-container-core-buttons-is-layout-b507c051 wp-block-buttons-is-layout-flex\">\n<div class=\"wp-block-button\"><a class=\"wp-block-button__link wp-element-button\" href=\"https:\/\/roder.it\/en\/contacts\/\">Click here !<\/a><\/div>\n<\/div>\n<\/div><\/div>\n\n<div style=\"height:30px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n<h2 class=\"wp-block-heading\">Laser Doppler principle<\/h2><p class=\"wp-block-paragraph\">The classic Doppler principle (DGV \u2014 Doppler Global Velocimetry, or LDV \u2014 Laser Doppler Velocimetry) uses two coherent laser beams that intersect over the measuring area, forming an interference grid with fringes of known spacing. When a point on the moving product crosses the fringes, the scattered light modulates its intensity at a frequency equal to the product speed divided by the fringe spacing. A photoelectric sensor measures the modulation frequency and the electronics calculate the speed. The method is highly precise and independent of the characteristics of the product, of vibration in the installation and of the working distance (within the focal zone).   <\/p><h2 class=\"wp-block-heading\">Cross-correlation principle<\/h2><p class=\"wp-block-paragraph\">The cross-correlation method uses two optical sensors (cameras or pixel arrays) placed a known distance apart along the direction of travel. Both acquire the surface structure of the product in real time (the natural pattern of roughness, graininess, printing or marking). Cross-correlation analysis calculates the time shift between the two signals: \u03c4 = d\/v, where d is the distance between the sensors and v the speed. The method is particularly reliable on products with a pronounced surface structure, and is robust against variations in the product (reflectivity, color, surface structure).   <\/p><h2 class=\"wp-block-heading\">Technical characteristics<\/h2><p class=\"wp-block-paragraph\">Industrial laser linear speed meters cover speed ranges from 0.1 m\/min to 6000 m\/min and beyond, with typical accuracy of 0.05% of the measured speed and 0.02% of the integrated length. Length resolution is typically 0.1 mm. The digital interfaces (Profinet, EtherCAT, Modbus, OPC UA) enable real-time integration with line systems. The typical working distance is 100-300 mm from the product, with a tolerance of \u00b115-30 mm on product position (important for the stability of an industrial setup). They are compact, with a rugged industrial design.   <\/p><h2 class=\"wp-block-heading\">Advantages over measuring wheels<\/h2><p class=\"wp-block-paragraph\">The main advantages over wheel-based systems are: no slip (the chronic problem of measuring wheels, which generates systematic errors in length); no contact with the product (eliminating marking, wear and contamination); applicability to hot products (rolling mill exit, hot extrusions); higher precision (0.05% for laser against a typical 0.5-1% for a wheel); reduced maintenance (no mechanical parts subject to wear); reliability over time (minimal calibration drift). The initial costs are higher, but the return on investment is positive for high-volume or high-precision applications. <\/p><h2 class=\"wp-block-heading\">Applications<\/h2><p class=\"wp-block-paragraph\">The industrial applications are: rolling lines for steel, aluminum and copper (speed and length control for the cutting program and for batch certificates); extrusion lines for tubes and profiles (calculating lengths produced and cut-to-length); wire and cable production (length control in production and for sale); rotary printing lines (synchronization and speed control for print registration); the textile industry for webs and nonwovens; the paper industry (paper and board reels); and the production of panels and laminates.<\/p><h2 class=\"wp-block-heading\">Selection criteria<\/h2><p class=\"wp-block-paragraph\">Selecting a laser VLM depends on the speed range, on the characteristics of the product (reflectivity, structure, temperature), on the width of the product (in order to size the measuring window), on integration with the line PLC and MES, on the IP protection rating for the industrial environment (typically IP65-IP67) and on maintenance requirements (cleaning of the optical windows). For lines with extreme speeds or precision, a feasibility study with preliminary trials on the real product is recommended. <\/p>\n<h2 id=\"prodotti-collegati\" class=\"wp-block-heading has-ti-accent-color has-text-color\">Related products<\/h2>\n\n<p class=\"wp-block-paragraph\">The RODER instruments for this application. Go to the relevant catalogue pages for models, technical data and documentation. <\/p>\n\n<div class=\"wp-block-group is-layout-grid wp-container-core-group-is-layout-b251d530 wp-block-group-is-layout-grid\">\n<div class=\"wp-block-group has-border-color has-white-background-color has-background is-layout-constrained wp-container-core-group-is-layout-10ff9433 wp-block-group-is-layout-constrained\" style=\"border-color:#e0e0e0;border-width:1px;border-radius:8px;padding:16px\">\n<figure class=\"wp-block-image size-large has-custom-border\"><a href=\"https:\/\/roder.it\/en\/products\/optical-encoder-speed-meters\/\"><img decoding=\"async\" src=\"https:\/\/roder.it\/wp-content\/uploads\/2026\/06\/astech-velocimetri_ottici_vlm500-appl_nastro_continuo_tappeti_continui-web_image-300x300-1.webp\" alt=\"Optical speed meters and encoders\" style=\"border-radius:6px;aspect-ratio:4\/3;object-fit:contain\"\/><\/a><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\" style=\"font-size:clamp(14px, 0.875rem + ((1vw - 3.2px) * 0.385), 17px);\"><a href=\"https:\/\/roder.it\/en\/products\/optical-encoder-speed-meters\/\">Optical speed meters and encoders<\/a><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\" style=\"font-size:14px\">VLM speed meters for non-contact measurement of speed and length.<\/p>\n\n\n\n<div class=\"wp-block-buttons is-layout-flex wp-block-buttons-is-layout-flex\">\n<div class=\"wp-block-button\"><a class=\"wp-block-button__link has-custom-font-size wp-element-button\" href=\"https:\/\/roder.it\/en\/products\/optical-encoder-speed-meters\/\" style=\"font-size:14px\">Browse the catalogue<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n\n<div class=\"wp-block-group is-layout-flow wp-block-group-is-layout-flow\">\n<div style=\"height:30px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h4 class=\"wp-block-heading has-ti-accent-color has-text-color has-link-color wp-elements-2\">Contacts &amp; Information<\/h4>\n\n\n\n<p class=\"wp-block-paragraph\">Contact for general information : <a href=\"mailto:info@roder.it\">info@roder.it<\/a><br\/><br\/>Machine Vision Division of RODER : <a href=\"https:\/\/www.visiotronix.com\">www.visiotronix.com<\/a><br\/>RODER Instruments Division : <a href=\"https:\/\/www.visiotronix.com\">www.innovacheck.com<\/a><br\/>More about RODER : <a href=\"https:\/\/roder.it\/en\/contacts\/\">about us<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The information contained in this website is provided for information purposes only. Although it has been prepared with the greatest care, it does not constitute a contractual offer or a binding commitment to supply. It may contain transcription, translation or typographical errors. For precise and up-to-date information, please contact our company directly.   <\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Note:<\/strong> Some images on this website have been intentionally generated using artificial intelligence (AI). This is because, for many applications and projects, photographs of the actual installation or system cannot be disclosed owing to confidentiality agreements, contractual clauses and non-disclosure agreements (NDAs). <\/p>\n\n\n\n<div style=\"height:30px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Laser linear speed meters for strip, sheet metal and moving products (VLM).<\/p>\n","protected":false},"author":157040980,"featured_media":0,"parent":19425,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_yoast_wpseo_focuskw":"","_yoast_wpseo_title":"","_yoast_wpseo_metadesc":"","_coblocks_attr":"","_coblocks_dimensions":"","_coblocks_responsive_height":"","_coblocks_accordion_ie_support":"","_wpcom_ai_launchpad_about_page":false,"_wpcom_ai_launchpad_gallery_page":false,"_wpcom_ai_launchpad_contact_page":false,"_wpcom_ai_launchpad_events_page":false,"_wpcom_ai_launchpad_video_page":false,"_wpcom_ai_launchpad_portfolio_piece":false,"_jetpack_hide_featured_image":false,"_jetpack_featured_image_duplicate_dismissed":0,"footnotes":""},"class_list":["post-24179","page","type-page","status-publish","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.8 - 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On this page, which is theoretical in approach, we compare these methods to clarify their advantages, limits and fields of application, with reference to ASTech optical velocimeters and encoders. The page\u2026","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"ASTECH VLM60: vista interna dello strumento","src":"https:\/\/i0.wp.com\/roder.it\/wp-content\/uploads\/2026\/06\/astech-velocimetri_ottici_vlm60-vlm60_vista_interna_dello_strumento-web_image-1000x1000-1.webp?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/roder.it\/wp-content\/uploads\/2026\/06\/astech-velocimetri_ottici_vlm60-vlm60_vista_interna_dello_strumento-web_image-1000x1000-1.webp?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/roder.it\/wp-content\/uploads\/2026\/06\/astech-velocimetri_ottici_vlm60-vlm60_vista_interna_dello_strumento-web_image-1000x1000-1.webp?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/roder.it\/wp-content\/uploads\/2026\/06\/astech-velocimetri_ottici_vlm60-vlm60_vista_interna_dello_strumento-web_image-1000x1000-1.webp?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":19425,"url":"https:\/\/roder.it\/en\/inspection\/rotation-speed-and-linear-motion\/","url_meta":{"origin":24179,"position":1},"title":"Rotation speed and linear motion","author":"GSM","date":"13 May 2026","format":false,"excerpt":"Tachometers, stroboscopes and linear speed meters for monitoring rotating machinery and production lines.","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":19951,"url":"https:\/\/roder.it\/en\/technologies\/optics-and-laser\/","url_meta":{"origin":24179,"position":2},"title":"Optics and LASER","author":"GSM","date":"29 June 2026","format":false,"excerpt":"Optical and laser technologies make it possible to measure the speed and length of a moving material without any physical contact. On this page we examine, from a technical standpoint, the principles on which ASTech optical speed meters and encoders are based: the spatial filter of the VLM500 series and\u2026","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"scanner laser misura di profilo e posizione","src":"https:\/\/i0.wp.com\/roder.it\/wp-content\/uploads\/2025\/02\/application_note_0001_scansione_laser_rilievo_posizione_aletta_per_saldatura_720x720.png?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/roder.it\/wp-content\/uploads\/2025\/02\/application_note_0001_scansione_laser_rilievo_posizione_aletta_per_saldatura_720x720.png?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/roder.it\/wp-content\/uploads\/2025\/02\/application_note_0001_scansione_laser_rilievo_posizione_aletta_per_saldatura_720x720.png?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/roder.it\/wp-content\/uploads\/2025\/02\/application_note_0001_scansione_laser_rilievo_posizione_aletta_per_saldatura_720x720.png?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":17941,"url":"https:\/\/roder.it\/en\/technologies\/","url_meta":{"origin":24179,"position":3},"title":"Technologies","author":"GSM","date":"29 June 2026","format":false,"excerpt":"Non-contact speed and length measurement is today a key technology for process control in many industrial sectors. Optical technologies make it possible to detect the movement of a material without touching it, eliminating the wear, slippage and machine downtime typical of measuring wheels and contact encoders. In this section we\u2026","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"archiviazione dati sul cloud con tecnologie wireless - industria 4.0","src":"https:\/\/i0.wp.com\/roder.it\/wp-content\/uploads\/2019\/05\/composizione_trasmissione_cloud.png?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/roder.it\/wp-content\/uploads\/2019\/05\/composizione_trasmissione_cloud.png?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/roder.it\/wp-content\/uploads\/2019\/05\/composizione_trasmissione_cloud.png?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/roder.it\/wp-content\/uploads\/2019\/05\/composizione_trasmissione_cloud.png?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":19263,"url":"https:\/\/roder.it\/en\/inspection\/speed-and-rotation-in-motion\/","url_meta":{"origin":24179,"position":4},"title":"Speed and rotation in motion","author":"GSM","date":"30 June 2026","format":false,"excerpt":"The speed of a moving material is a central physical quantity in process control: drive synchronisation, cutting to length, metre counting and line regulation all depend on it. In this Inspection section we examine the quantity \u201cspeed\u201d in its various forms \u2014 surface, linear, multidimensional \u2014 and the methods for\u2026","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":23440,"url":"https:\/\/roder.it\/en\/inspection\/diameter-ovality-profile-and-form\/non-contact-width-and-length-gauges\/","url_meta":{"origin":24179,"position":5},"title":"Non-contact width and length gauges","author":"GSM","date":"13 May 2026","format":false,"excerpt":"Laser and optical instruments for the non-contact measurement of the width and length of webs, sheet metal and profiles.","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"_links":{"self":[{"href":"https:\/\/roder.it\/en\/wp-json\/wp\/v2\/pages\/24179","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/roder.it\/en\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/roder.it\/en\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/roder.it\/en\/wp-json\/wp\/v2\/users\/157040980"}],"replies":[{"embeddable":true,"href":"https:\/\/roder.it\/en\/wp-json\/wp\/v2\/comments?post=24179"}],"version-history":[{"count":3,"href":"https:\/\/roder.it\/en\/wp-json\/wp\/v2\/pages\/24179\/revisions"}],"predecessor-version":[{"id":24182,"href":"https:\/\/roder.it\/en\/wp-json\/wp\/v2\/pages\/24179\/revisions\/24182"}],"up":[{"embeddable":true,"href":"https:\/\/roder.it\/en\/wp-json\/wp\/v2\/pages\/19425"}],"wp:attachment":[{"href":"https:\/\/roder.it\/en\/wp-json\/wp\/v2\/media?parent=24179"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}