1 / 9

Electronic Distance Measurement

Electronic Distance Measurement. - Physics and Application to Structural Engineering Research – 11 March 2014 J. M. Lynch CEE 398 KUC. Evolution of EDM Instruments. Got its start in 1948 with Swiss device using visible light (range=40km only at night) http://www.gmat.unsw.edu.au

elie
Télécharger la présentation

Electronic Distance Measurement

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Electronic Distance Measurement - Physics and Application to Structural Engineering Research – 11 March 2014 J. M. Lynch CEE 398 KUC.

  2. Evolution of EDM Instruments • Got its start in 1948 with Swiss device using visible light (range=40km only at night) http://www.gmat.unsw.edu.au • Microwaves used in 1957 (range=80km) http://www.gmat.unsw.edu.au • Infra-red, IR, devices are common today http://www.pentaxcanada.ca

  3. EDM Physics Lesson • Electro-magnetic energy travels through the atmosphere according to the following: • Where: • c = speed of light in vacuum • n = atmospheric index of refraction, 1.003 for STP • f = frequency of the electro-magnetic energy • l = wavelength of the energy http://131.251.21.249/squ1/

  4. l l l l EDM P l l l EDM Physics Lesson (continued) • The propagation of electro-magnetic radiation may be used to measure distances as shown below • If the round-trip distance is not an integer number of wavelengths, the partial wavelength may be measured by noting the phase shift of the returning signal.

  5. EDM Physics Lesson (continued) • The distance between EDM and reflector is expressed • Counting the number of complete wavelengths “n” would require very accurate measurement of time • Instead, longer wavelength signals are sent as demonstrated below Therefore, 2L = 252.806 m

  6. EDM Physics Lesson (continued) • Modern instruments use Amplitude Modulation (AM) to generate multiple wavelengths from the same radiation source. http://www.tm.agilent.com/data/static/eng/tmo/Notes/interactive/an-150-1/classes/liveAM.html • This is done for economics reasons and also to make the units smaller, lighter, and less power hungry. • The “carrier wave” used for most modern EDM instruments is generated by a Gallium-Arsenide-Diode Laser at l = 900 nm.

  7. Current EDM Instruments • So called “total-station” instruments package a digital theodolite (for measuring azimuth and altitude) with an EDM, data storage device, and often a modem for transmitting data from the field. • The most common instruments use a “pulse” of 2 to 4 AM frequencies ranging from 150kHz to 15MHz. • This range of frequencies have corresponding “half-wavelengths” of 1.0km to 10m, respectively. http://www.nikon.co.jp/survey-e

  8. Application to Structural Engineering • Use of EDM on the scale of m-strain measurements is postulated as follows: • Approx. cracking strain of concrete = 40me • Use a gage length of 100mm • Distance accuracy measurement needs to be on the order of • Therefore, l = 1mm or 0.1mm would be needed to obtain the specified distance resolution • This wavelength corresponds to the IR and RADAR regions of the electro-magnetic spectrum • (NOTE: AM is not likely to be appropriate given that the carrier wave would have a wavelength on the order of the desired AM signal)

  9. EDM EDM Reflector Test Specimen Application to Structural Engineering • Assuming that displacement measurements of the required accuracy can be obtained . . . • An array of reflectors and two radiation sources are positioned as shown

More Related