[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"detail-sidebar-cat-0-en-105":3,"doc-seo-398195-105":59,"doc-detail-398195-en":130},{"code":4,"msg":5,"data":6},0,"success",[7,13,18,23,28,33,38,43,48,51,55],{"id":8,"doc_module":4,"doc_module_name":9,"category_name":10,"show_sort_weight":11,"slug":12},1,"Document","Story & Novel",90,"story-novel",{"id":14,"doc_module":4,"doc_module_name":9,"category_name":15,"show_sort_weight":16,"slug":17},2,"Literature",80,"literature",{"id":19,"doc_module":4,"doc_module_name":9,"category_name":20,"show_sort_weight":21,"slug":22},4,"Exam",70,"exam",{"id":24,"doc_module":4,"doc_module_name":9,"category_name":25,"show_sort_weight":26,"slug":27},5,"Comic",60,"comic",{"id":29,"doc_module":4,"doc_module_name":9,"category_name":30,"show_sort_weight":31,"slug":32},6,"Technology",50,"technology",{"id":34,"doc_module":4,"doc_module_name":9,"category_name":35,"show_sort_weight":36,"slug":37},7,"Healthcare",40,"healthcare",{"id":39,"doc_module":4,"doc_module_name":9,"category_name":40,"show_sort_weight":41,"slug":42},8,"Research & Report",30,"research-report",{"id":44,"doc_module":4,"doc_module_name":9,"category_name":45,"show_sort_weight":46,"slug":47},9,"Religion & Spirituality",20,"religion-spirituality",{"id":46,"doc_module":4,"doc_module_name":9,"category_name":49,"show_sort_weight":46,"slug":50},"World Cup","world-cup",{"id":52,"doc_module":4,"doc_module_name":9,"category_name":53,"show_sort_weight":52,"slug":54},10,"Lifestyle","lifestyle",{"id":56,"doc_module":4,"doc_module_name":9,"category_name":57,"show_sort_weight":24,"slug":58},19,"General","general",{"code":4,"msg":60,"data":61},"ok",{"site_id":62,"language":63,"slug":64,"title":65,"keywords":66,"description":67,"schema_data":68,"social_meta":123,"head_meta":125,"extra_data":127,"updated_unix":129},105,"en","traversing-a-duct-application-note-tsi-106","Traversing a Duct - Application Note TSI-106","","Application note detailing practical methods to determine average air velocity or volumetric flow rate inside ducts using a velocity probe or pitot-static tube. It explains why averaging pressure before converting to velocity can produce incorrect results and provides the correct pressure-to-velocity relationship. Guidance covers where to place traverse measurements relative to duct turns or obstructions, equivalent diameter for rectangular ducts, and correction for single-point center readings. It further describes log-Tchebycheff traverse schemes for round and square ducts with required measuring-point distributions, insertion-depth calculation, and computation of flow rate.",{"@graph":69,"@context":122},[70,84,105],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":30,"@type":76,"position":81},"https://docshare.wps.com/document/technology/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/traversing-a-duct-application-note-tsi-106/398195/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/traversing-a-duct-application-note-tsi-106/398195.png","ImageObject",300,407,{"name":92,"@type":93},"Stanley","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-09-29","2026-09-27",true,{"@type":102,"interactionType":103,"userInteractionCount":14},"InteractionCounter",{"@type":104},"ViewAction",{"@type":106,"mainEntity":107},"FAQPage",[108,114,118],{"name":109,"@type":110,"acceptedAnswer":111},"Why is averaging pitot pressure before converting to velocity incorrect?","Question",{"text":112,"@type":113},"Because pitot-tube velocity is proportional to the square root of pressure, so pressure averaging distorts the resulting velocities. The note warns this can especially affect cases where readings deviate by more than ±25% from the average pressure.","Answer",{"name":115,"@type":110,"acceptedAnswer":116},"How far upstream and downstream should duct traverse measurements be taken?",{"text":117,"@type":113},"For best accuracy, measure at least 7.5 duct diameters downstream and at least 3 duct diameters upstream from turns or flow obstructions. Shorter distances (as little as 2 downstream and 1 upstream) are possible but reduce measurement accuracy.",{"name":119,"@type":110,"acceptedAnswer":120},"What is the recommended point layout for traversing a round duct using the log-Tchebycheff method?",{"text":121,"@type":113},"The duct is divided into concentric circles with equal area, and readings are taken from each circular area. Commonly, three circles (6 points per diameter) are used for ducts ≤10 inches, while four or five circles (8 or 10 points per diameter) are used for ducts larger than 10 inches.","https://schema.org",{"og:url":83,"og:type":124,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":126,"canonical":83},"index,follow",{"doc_id":128,"site_id":62},398195,1790672042,{"code":4,"msg":5,"data":131},{"doc_id":128,"user_id":132,"nickname":92,"user_avatar":133,"doc_module":4,"category_id":29,"category_name":30,"doc_title":65,"doc_description":67,"doc_content":134,"file_id":135,"file_url":136,"file_type":137,"file_size":138,"view_count":14,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":19,"language":139,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":140,"faqs":141,"seo_title":142,"seo_description":67,"update_tm":143,"read_time":52},2336477405376,"https://ap-avatar.wpscdn.com/davatar_29158cc5080c5b710cf443261637dec0","TRAVERSING A DUCT  \nTO DETERMINE  \nAVERAGE AIR VELOCITY OR VOLUME  \nAPPLICATION NOTE TSI-106 (A4)  \nThe following techniques can be used to measure air flow inside ducts, using a velocity probe or pitot-static tube. When using a pitot-static tube, the individual velocities must be calculated for each pressure reading, then averaged together. Averaging pressure with a pitot tube and then converting into velocity will give an incorrect result, especially if many readings are more than ±25% from the average pressure. Remember that for a pitot tube, velocity is proportional to the square root of pressure.  \nWhere to Take the Measurement  \nIn order to make air velocity measurements in a duct, it is best to measure at least 7.5 duct diameters downstream and at least 3 duct diameters upstream from any turns or flow obstructions. It is possible to do a traverse as little as 2 duct diameters downstream and 1 duct diameter upstream from obstructions, but measurement accuracy will be impaired. When measuring rectangular ducts, use this formula to find the equivalent diameter of the duct when calculating how much distance is 7.5 diameters downstream and 3 diameters upstream:  \nEquivalent Diameter = sq root of 4HV / Pi  \nWhere:  \nH = horizontal duct dimension  \nV = vertical duct dimension  \nPi = 3.14  \nIt is also possible to take a single reading to measure air velocity or air volume flow in a duct, measuring in the center of the duct and multiplying the reading by 0.9 to correct for the higher velocity at the center of the duct. If conditions are very good an accuracy of ±5 or ±10 percent maybe obtained this way. However, this method is not reliable and should only be used where small duct size or other conditions do not permit a full traverse.  \nTraversing a Round Duct  \nUsing the log-Tchebycheff method, the duct is divided into concentric circles, each containing equal area. An equal number of readings is taken from each circular area, thus obtaining the best average. Commonly, three concentric circles (6 measuring points per diameter) are used for ducts of 10-inch diameter and smaller. Four or five concentric circles (8 or 10 measuring points per diameter) are used for ducts larger than 10-inch diameter.  \nThe preferred method is to drill 3 holes in the duct at 60° angles from each other as shown in figure 1 below. Three traverses are taken across the duct, averaging the velocities obtained at each measuring point. Then the average velocity is multiplied by the duct area to get the flow rate. (A different method uses 2 holes at 90° from each other, decreasing the number of traverses with the probe by one.)  \nFigure 1: Location of measuring points when traversing around duct using log-Tchebycheff method  \n\n| \\#of Measuring Points Per Diameter | Position Relative to Inner Wall |\n| --- | --- |\n| 6 | 0. 032, 0. 135, 0. 321, 0. 679, 0. 865, 0.968 |\n| 8 | 0. 021, 0. 117, 0. 184, 0. 345, 0. 655, 0. 816, 0. 883, 0.979 |\n| 10 | 0. 019, 0. 077, 0. 153, 0. 217, 0. 361, 0. 639, 0. 783, 0. 847, 0. 923, 0.981 |\n\nBefore taking the measurement, multiply the numbers in the table times the duct diameter to get insertion depth for the probe. (Do not forget to use the inside dimension of the duct if it is lined with insulation.)  \nTraversing a Square Duct  \nUsing the log-Tchebycheff method, the duct is divided into rectangular areas, which are further adjusted in size to account for effects of the duct wall on the air flow. A minimum of 25 points must be measured in order to get a good average. The number of data points to be taken along each side of the duct depends on how wide that side of the duct is. For duct sides less than 30 inches,  \n5 traversal points must be taken along that side. For duct sides of 30 to 36 inches, 6 points must betaken. For duct sides greater than 36 inches, 7 points must be taken. Multiply the numbers in the table times the duct dimension to get insertion depth for the probe.  \nFigure 2: Location of measuring points for traver","cbCaisCdUY7SIofK","https://ap.wps.com/l/cbCaisCdUY7SIofK","pdf",199782,"English","# Where to Take the Measurement\n## Traversing a Round Duct\n## Traversing a Square Duct\n# Disclaimer","[{\"question\":\"Why is averaging pitot pressure before converting to velocity incorrect?\",\"answer\":\"Because pitot-tube velocity is proportional to the square root of pressure, so pressure averaging distorts the resulting velocities. The note warns this can especially affect cases where readings deviate by more than ±25% from the average pressure.\"},{\"question\":\"How far upstream and downstream should duct traverse measurements be taken?\",\"answer\":\"For best accuracy, measure at least 7.5 duct diameters downstream and at least 3 duct diameters upstream from turns or flow obstructions. Shorter distances (as little as 2 downstream and 1 upstream) are possible but reduce measurement accuracy.\"},{\"question\":\"What is the recommended point layout for traversing a round duct using the log-Tchebycheff method?\",\"answer\":\"The duct is divided into concentric circles with equal area, and readings are taken from each circular area. Commonly, three circles (6 points per diameter) are used for ducts ≤10 inches, while four or five circles (8 or 10 points per diameter) are used for ducts larger than 10 inches.\"}]","Traversing a Duct - Application Note TSI-106 | PDF",1790473465]