ELECTRONIC INSTRUMENTS - allow a rapid and accurate determination of linear distances, horizontal and vertical angles suitable even for large extent surveys requiring higher orders of precision
BASIC PRINCIPLE OF EDM
The TIME required for a RADIO/LIGHT WAVE to travel from one end of a line to the other is a function of LENGTH MEASURED.
CLASSIFICATION OF EDM
• ELECTRO-OPTICAL INSTRUMENTS
• MICROWAVE INSTRUMENTS
ELECTRO-OPTICAL INSTRUMENTS - type of instruments which transmit wavelengths within or slightly
beyond the visible region of the spectrum.
MICROWAVE INSTRUMENTS - this type of EDM transmits microwaves corresponding to wavelengths of about 1.0 to 8.6mm. It can operate even during a drizzle or a fog.
2 IDENTICAL UNITS OF MICROWAVE INSTRUMENT
TRANSMITTER & RECEIVER
EDM INSTRUMENTS -Used for determining linear measurements required in traversing, engineering construction, optical tooling, triangulation, trilateration and various tasks where
precise measurements or layouts are needed.
-They are extremely useful in measuring distances over rough and rugged terrain which are difficult to access.
SHORTRANGE - does not exceed to 25 km
-most instruments are electro-optical type
MEDIUM RANGE - 25-75km range
-either microwave or electro-optical type
-used in land and construction survey
LONG RANGE - 75 km longer
-instruments in this group transmits radio waves
-
used in hydrographic survey
GEODIMETER -it projects pulsating visible light beam to a reflector which returns the light to the instrument
-invented by ERIK BERGSTRAND in 1948
TELLUROMETER -it utilized high frequency microwave transmission and was capable of measuring distance up to 80 km day or night
