Electronic Distance Measurement

BY:Mr. Aman Bathla (A.P.)

INTRODUCTIONDistance 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)

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

EDM EQUIPMENT CLASSIFICATIONs

On the basis of Range of Operation

EDM EQUIPMENT CLASSIFICATIONs

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

EDM INSTRUMENTs

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

BASIC FUNCTION

Generation Modulation

Transmission

Propagation Reflection

Reception

MODULATION & DEMODULATION

Carrier WaveHigh freq Wave

Measuring Signal

Measured Signal

OPERATIONSSetting 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

DISTANCE MEASUREMENT

Distance = Velocity x Time 2Time is too short- difficult to measurePhase Difference method is Used

DISTANCE MEASUREMENTPhase Difference method

Equivalent Distance when Received Signal Out of Phase

Length of wave

= Phase Difference of wave transmitted & receivedʎ = Wavelength

n = No. of wave travelled

ERRORs IN EDM

Personal Errors

Instrumental Errors

Natural Errors

ERRORs IN EDM

Personal Error

Inaccuracy in Initial Setups

Instrument & Reflector

measurements going Wrong

Atmospheric Pressures & Temperature

Determination errors

ERRORs IN EDM

Instrumental Error

Calibration Error

Chances of getting unstable frequent

errors Errors Shown by

Reflector

ERRORs IN EDM

Natural Error

Atmospheric variations in

Temperature, Pressure & Humidity

Multiple Refraction of Signals

Any Question?