Methodology

1)Determination of EDM zero correction:

The approach for determining the zero correction of an EDM was to divide a long straight line into parts. The approach for determining the zero correction of an EDM is to divide a long straight line into parts. The appropriate sections were measured, as well as the long line, and the zero correction was computed.

2)Setting out of base line:

A theodolite and ranging poles are used to set out the baseline. set up the theodolite on the starting point after a pillar has been placed. The direction is defined by pointing the theodolite in the predetermined direction. place the beacons at the two ends of the baselines. Use the EDM work in conjunction with theodolite and the battery fixed. It has to be then set over pillar and level the reflector too. After that, the following operation should be carried out

The height of EDM instrument and reflector’s height are measured with line tape and record in the field book. The intension is to determine the slope correction to bring the measured slope distance to horizontal distance. Reflector is then sighted, the prism’s center is bisected, and the theodolite’s vertical and horizontal movement is clamped. Checks for a battery and turns on the instrument’s on/off switch to make the signal.

The display reads 0000, which means the instrument is ready to use. The “MEASURE” knob is softly touched to start the measurement. The distance measurement is completed automatically in less than 5 seconds, during which time points on the digital display flash and the measured distance is displayed.

• For slope correction, the theodolite’s vertical angle reading is recorded.
• The temperature of the atmosphere is also taken into account.

3)EDM Measurement:

To measure any distance, you simply compare it to a known or calibrated distance for example by using a scale or tape to measure the length of an object in EDM’s the same comparison principle is used the calibrated distance in this case is the wavelength of the modulation on a carrier wave.

1. Modern EDM’s use the precision of a quartz crystal oscillator and the measurement of phase shift to determine the distance.
2. The EDM is set up at one end of the distance to be measured and a reflector at the other end.
3. The EDM generates an infrared continuous wave carrier beam which is modulated by an electronic shutter.
4. This beam is then transmitted through the aiming optics to the reflector.
5. The reflector returns the beam to the receiving optics where the incoming light is converted to an electrical signal allowing a phase comparison between transmitted and received signals.
6. The amount by which the transmitted and received wavelengths are out of phase can be measured electronically and registered on a meter to within a millimeter or two.

The advent of EDM equipment has completely revolutionaries all surveying procedures and resulted in a change of emphasis and techniques, by reason of the fact that distance can now be measured quickly and accurately, regardless of terrain condition.