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The measurement does not need to be affected by these since the first recorded return will normally be the head of the emitted wave traveling at the shortest distance which is equivalent to the thickness of the sample.
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The sound wave has a spherical pattern of propagation and will undergo different phenomena like multipath reflection or diffraction. The wave is usually emitted by a piezoelectric cell or EMAT sensor that is built into the measurement sensor head and the same sensor is used to record the reflected wave. Thus, the time corresponds to traversing the sample twice. The formula features division by two because usually the instrumentation emits and records the ultrasound wave on the same side of the sample using the fact that it is reflected on the boundary of the element. L m is the velocity of sound in the given sample Thus, given this information, called celerity, one can calculate the length of the path traversed by the wave using this formula: Ultrasonic waves have been observed to travel through metals at a constant speed characteristic to a given alloy with minor variations due to other factors like temperature. This type of measurement is typically performed with an ultrasonic thickness gauge. In the field of industrial ultrasonic testing, ultrasonic thickness measurement ( UTM) is a method of performing non-destructive measurement (gauging) of the local thickness of a solid element (typically made of metal, if using ultrasound testing for industrial purposes) based on the time taken by the ultrasound wave to return to the surface. JSTOR ( June 2009) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed.įind sources: "Ultrasonic thickness measurement" – news Please help improve this article by adding citations to reliable sources. This is the final element in an NTS map number for a 1:50 000 map.This article needs additional citations for verification. The numbering begins in the southeast (lower right-hand) corner and zigzags to the northeast (upper right-hand) corner. This lighter grey extent is divided into 16 areas defined by fine black lines each of these 16 areas is labelled with a black number (" 1" to " 16"). The letter is the second element in an NTS map number for a 1:250 000 map. The lettering begins in the southeast (lower right-hand) corner and zigzags to the northeast (upper right-hand) corner. This dark grey extent is divided into 16 smaller areas defined by lighter grey lines each of these 16 areas is labelled with a light grey letter (" O" and " J", in the diagram). This is the first element in an NTS map number. How are NTS map sheets defined?Įach area defined by dark grey lines is given a dark grey number (" 21", in the diagram).
Digital thickness grid mapping download#
You can download them in PDF, TIFF, Shapefile and KML formats via Open Government. These index maps are available from map dealers, Regional Distribution Centres, and Certified Map Printers across Canada.
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Digital thickness grid mapping series#
We have developed the following series of six regional Index Maps showing the National Topographic System (NTS) grid: