Two Peg Test

INTRODUCTION

▪ Two Peg Test is a surveying operation carried out to determine whether the levelling bubble and telescope line of sight are parallel.

OBJECTIVE

▪ Peg Test is a surveying operation carried out to determine if the leveling bubble (bubble axis) and telescope line-of-sight (line of collimation) are parallel.

THEORY

▪ By using the leveling method, work for establishing Temporary Bench Mark (TBM)

was done

▪ Bench Mark (BM) must be known first. BM point determined by Land Surveyor is final.

▪ Distances between backsight and foresight must be more or less equivalent to avoid collimation errors.

▪ The survey work is to ensure so that the true error is smaller than the permissible error.

▪ Bench Mark (BM) is a fixed point on the Earth surface which its level is known height of collimation is line of collimation level from datum.

▪ Temporary Bench Mark (TBM) is a nearest point as reference if the Bench Mark (BM) is far from surveying area.

▪ Backsight is the first sight taken after temporary leveling of the instrument has been carried out.

▪ Foresight is last sight taken before the instrument is transferred to another point.

INSTRUMENT

▪ Level and Tripod (1 set)

▪ Staff (2 sets)

▪ Staff bubble (2 sets)

▪ Tape (1 set)

PROCEDURE

▪ Each group will be required to perform a peg test to check the instrument.

▪ Each person in the group should record the results of the Peg Test in their own field book.

▪ Set out and mark on the ground (with wooden pegs driven into the Earth, or roofing nails in tar) two point some 30 m apart.

▪ Set up instrument midway between two pegs [setup 1].

[pic]

▪ Read staff on each peg (backsight and foresight), and calculate height difference.

▪ Next, move instrument about L/10 = 3 m beyond one of the pegs (normally fore staff position, [setup 2]

[pic]

▪ Read