Measuring Principles

Although there are many EDM instruments available, there are basically only two methods of measurement employed, namely the pulse method and the more popular phase difference method.

Pulse method

A short, intensive pulse of radiation is transmitted to a reflector target, which immediately transmits it back, along a parallel path, to the receiver. The measured distance is computed from the velocity of the signal multiplied by the time it took to complete its journey, i.e.