Edm is a surveying instrument used to measure the distance electronically. This Surveying Instrument is used in triangulation to measure the length of Base line because more accuracy is required to measure the length of base line.

2. Distance Measurement by Electronic method
Based on Hard-wired algorithm
Relay on Propagation, Reflection and
subsequent reception of electro-magnetic Wave
Electronic Angle Measurement (Combined the
function of theodolite & EDM – TOTAL STATION)

3. Short Range
• Range<3km
• ±(0.2+1mm/km)
accuracy
• Telluromerter
Medium Range
• Range<25km
• ±(5+1mm/km)
accuracy
• Geodimeter
Long Range
• Range<100km
• ±(10+3mm/km)
accuracy
• Distomat
On the basis of Range of Operation

4. On the basis of carrier wave Used
Microwave
• Long range
instrument
• Freq range
3 -30GHz
• Telluromerter
Visible light
• Medium range
instrument
• Freq used
5 x 1014 Hz
• Geodimeter
Infrared
• Short range
instrument
• Freq used
3 x 1014 Hz
• Distomat

5. Geodimeter
Heavier Instrument
Observations are limited to nights
only
Instrument set up at one end &
reflector at other end
Light Radio Waves are used
Tellurometer
Lighter Instrument
Observations may be made during
the day as well as during the night
Two identical instruments at either
ends
High Frequency Radio Waves are
used

6. Generation Modulation Transmission Propagation
ReflectionReceptionDemodulation
Distance
Measured

7. Carrier Wave
High freq Wave
Measuring
Signal
Measured Signal

8. Setting up Instrument is centered over a station by means of
tribrach. Reflector are set over the remote station on tribrach
Aiming Instrument is aimed at prism by using sighting device
or theodolite telescope
Measurement Operator presses the measure button to
record the slope distance that displayed on LCD panel
Recording Information on LCD panel can be recorded
manually or automatically

9. Distance = Velocity x Time
2
Time is too short- difficult
to measure
Phase Difference method
is Used

10. Distances are calculated
Length of wave is known
No. Of Completed & Uncompleted Wave Is Measured Equivalent Distance when
Received Signal Out of Phase
Length of wave
= Phase Difference of wave
transmitted & received
ʎ = Wavelength
n = No. of wave travelled

11. Personal Errors
Instrumental Errors
Natural Errors

12. Personal
Error
Inaccuracy in
Initial Setups
Instrument &
Reflector
measurements
going Wrong
Atmospheric
Pressures &
Temperature
Determination
errors

13. Instrumental
Error
Calibration
Error
Chances of
getting
unstable
frequent errors
Errors Shown
by Reflector

14. Natural
Error
Atmospheric
variations in
Temperature,
Pressure &
Humidity
Multiple
Refraction of
Signals

15. Any Question?