This instrument employs modulated microwaves.Īs years passed technology has improved drastically. The second instrument for EDM was designed and developed in Africa in the year 1957, named tellurometer. Geodimeter is geodetic distance meter developed based on a modulated light beam. The first EDM instrument called geodimeter was developed in Sweden in the year 1948. Origin of Electronic Distance MeasurementĮlectronic distance measurement can be done by instruments like geodimeter, tellurometer or distomat etc. Error in Electronic Distance Measurement Instruments.Measurement of distance with EDM and a Reflector.Operations of Electronic Distance Measurement Instruments.Types of Electronic Distance Measurement Instrument.Origin of Electronic Distance Measurement.Knowing the length of wave, distances are calculated.īuilt up microprocessors provided in the instrument calculate the distances and display it by liquid crystal display (LCD). The improved techniques use phase difference method in which the number of completed wave and incomplete wave is measured.
However time is too short, measuring the time taken is difficult. The time taken by the wave to travel this 2x distance may be measured and knowing the velocity of wave, the distance may be calculated. They are reflected at the point up to which distance is to be measured from the instrument station and again received by the instrument. In EDM instruments these waves are generated, modulated and then propagated. The spectrum of an electromagnetic wave is as shown below:Īmong these waves microwaves, infrared waves and visible light waves are useful for the distance measurement.
Sun light or artificially generated electromagnetic wave consists of waves of different lengths. In this method instruments are used to measure distance that rely on propagation, reflection and reception of electromagnetic waves like radio, visible light or infrared waves. Above all we have EDM with an accuracy of 1 in 10 5, having a distance range of 100km.Įlectronic distance measurement in general is a term used as a method for distance measurement by electronic means. It is limited to 15 to 150m with an accuracy of 1 in 1000 to 1 in 10000. Still it gained a disadvantage of limited range of measurement. When large amount of inconsistency in the terrain or large obstructions exist, this method is avoided.Īs an alternative to this optical distance measurement method was developed. These are carried out with the help of optical wedge attachments.ĮDM or Electromagnetic distance measurement - The method of direct distance measurement cannot be implemented in difficult terrains. ODM or Optical distance measurement - This measurement is conducted by tacheometry, horizontal subtense method or telemetric method. 🕑 Reading time: 1 minuteElectronic distance measuring instrument is a surveying instrument for measuring distance electronically between two points through electromagnetic waves.Įlectronic distance measurement (EDM) is a method of determining the length between two points, using phase changes, that occur as electromagnetic energy waves travels from one end of the line to the other end. As a background, there are three methods of measuring distance between two points:ĭDM or Direct distance measurement - This is mainly done by chaining or taping.
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