ELECTROMAGNETIC DISTANCE MEASURING INSTRUMENTS
Sun light or artificially generated electromagnetic waves consist of waves of different lengths. Spectrum of an electromagnetic wave is shown below:
Among these waves microwaves, visible light waves and infrared waves are useful for the distance measurement. These waves are generated, modulated and then propagated in EDM instruments. At the point up to which distance is to be measured they are reflected from the instrument station and again retain by the instrument. Time taken by the wave to travel this 2x distance can be measured and by knowing the velocity of wave, the distance may be calculated. Though time is too short, measuring the time taken is hard. The improved techniques utilized phase difference method in which the number of completed and incomplete wave is measured. Distances are calculated by knowing the length of wave. Built up microprocessors provided in the instrument calculate the distances and by liquid crystal display (LCD) display it.
EDM instruments can be classified into the following three types:
- Micro wave instruments
- Infrared wave instruments
- Light wave instruments.