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Accuracy of EDM device ( In per KM)
3 cm to 4 cm
5 mm to 10 mm
10 cm to 18 cm
10 mm to 18 mm
5 mm to 10 mm
Electronic Distance Measurement (EDM) instruments are designed to measure distances using electromagnetic waves. The inherent accuracy of modern commercial EDM devices typically ranges from ┬▒(5┬аmm+5┬аppm) to ┬▒(10┬аmm+10┬аppm), which corresponds to an error of 5 mm to 10 mm per kilometer. Thus, Option B provides the standard expected error range per km.
Electronic Distance Measurement (EDM) instruments are designed to measure distances using electromagnetic waves. The inherent accuracy of modern commercial EDM devices typically ranges from ┬▒(5┬аmm+5┬аppm) to ┬▒(10┬аmm+10┬аppm), which corresponds to an error of 5 mm to 10 mm per kilometer. Thus, Option B provides the standard expected error range per km.
Accuracy=┬▒(a+b├ЧD) тАФ Total EDM error, where a is constant error (mm), b is variable error (ppm), and D is distance (km)
$\text{Error per km} = \pm (5\text{ mm} + 5\text{ ppm} \times 1\text{ km}) = \pm 10\text{ mm}$$ тАФ Maximum typical specified error per kilometer
EDM instruments emit a continuous wave or pulse of electromagnetic radiation (light or infrared) toward a reflector target placed at the remote station. The target reflects the wave back to the receiver, where the instrument determines distance by measuring the phase delay or time-of-flight of the returned signal.
EDM distance measurement accuracy is expressed as a combination of a fixed error in millimeters and a proportional error in parts per million (ppm).
For short to medium range measurements (up to 1 km), the constant instrumental error (5 mm to 10 mm) dominates the measurement uncertainty.
Atmospheric correction factors (temperature and pressure adjustments) are vital to maintain the specified ppm accuracy.
Provides extremely high speed and high accuracy compared to conventional taping or chaining.
Reduces manual measurement errors over long and rugged terrain.
Requires proper calibration and line-of-sight visual paths.
Atmospheric variations (refractive index changes) affect wave velocity and measurement precision.
Geodetic and topographic surveying.
Control survey for large infrastructure projects like highways, dams, and railways.
Option A (3 cm to 4 cm) represents chaining error limits on rough terrain, which is far too coarse for an EDM instrument.
Options C and D give incorrect magnitude ranges not aligned with standard survey-grade EDM specifications.
B is correct тАФ Standard survey-grade EDM instruments have an accuracy specification in the range of 5 mm to 10 mm per kilometer.
Remember that EDM precision relies on both constant error (a) and variable scale error (b┬аppm). At 1 km, 1┬аppm=1┬аmm, so a ┬▒(5┬аmm+5┬аppm) spec equals ┬▒10┬аmm total error.
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