Report Two Peg Test

INTRODUCTION In surveying, one of the basic component to measure is height for example to get the z value of point positioning x,y,z. leveling is the method available for determine height. In the world, leveling is a vertical measurement. It is process of measuring the difference in height between two or more point. The process of leveling is to measure height differences and to sum these to get the height of other point. Using the instrument called a level, the height on the staff are read and the difference in the value is the height differences. Whenever a level is set up, it is essential that the line of collimation, as viewed through the eyepiece, is horizontal. So far, the assumption has been made that once the circular bubble is centralised with the footscrews, then the line of collimation is set exactly horizontal by the compensator and diaphragm or by centralising the bubble in the spirit level tube. However, because they are in constant use on site and therefore subjected to inevitable knocks and bumps, most level are not in perfect adjustment and if horizontal reading are not being taken when it has been set up properly, a collimation error is present in the level. Since most levels will have a collimation error, some method is required to check this to determine if this error is within accepted limits. The most commonly used method is two- peg test which should be carried out when using a new or different level for the first time and at regular intervals after this depending on how much the level has been used. If the collimation error is found to be less than about ± 1mm per 20m or some specific value the level assumed to be in adjustment. If the collimation error is found to be greater than about ± 1mm per 20m or some specific value the level has to be adjusted. For some levels, the compensator has to be adjusted. This causes the spirit level bubble to move from the centre of its run, so it is brought back to the centre by adjusting the vial. All the mechanical adjustment for adjusting a level for collimation error are very difficult to do, especially on site, and if a level has an unacceptable collimation error, it should be adjusted by a trained technician preferable under laboratory conditions.

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OBJECTIVE 1. To carry out two peg test of leveling. 2. To compute the collimation error of level instrument. 3. To eliminate the error in level instrument, INSTRUMENT 1. 2. 3. 4.

1 x level 2 x staff 1 x tripod 1 x tape

METHODOLOGY 1. Mark point A and B with distance more than 40 meters. 2. Set level at C at equal distance on line AB (L). 3. Measure staff at point A(S2) and B(S1).

4. Move the level instrument near to point B at L/10 distance. 5. Measure staff A (S3) and D (S4).

DATA

PROCESSING 2

The reading obtained from a two-peg test carried out on a automatic level with a single level staff set up alternately at two peg A and B placed 50 m apart were as follows:

1. With the level midway between A and B Staff reading at A = 1.352m Staff reading at B =1.402m 2. With the level positioned 5m from peg B on the line AB produced. Staff reading at A = 1.444m Staff reading at B = 1.379m

RESULT S1=1.402m , S2 = 1.352m , S3 = 1.379m , S4 =1.444m Collimation error, e = (S1 – S2)-(S3-S4) = (1.402 – 1.352) – (1.379 – 1.444) = 0.115 For the instrument in position 5 m from peg B, the reading that should have been obtained on the staff when held at A is S’4 = 1.444 – [0 .115/ 50] 55 = 1.3175m

This is checked by computing (S’3 – S’4) and by comparing with (S1 – S2) as follows S’3 = 1.379 –[0.115 / 50] 5 = 1.3675 = (S1 – S2)

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Hence (S’3 –S’4) = 1.3675 – 1.3175 = 0.05 = (S1-S2) (check)

REFERENCES 1. Surveying for Engineers, A/Professor Sr Dr. Hj. Abd. Manan Bin Hj. Samad, Levelling. Lecturer Note (2012). 2. Surveying For Engineers, A/Professor Sr Dr. Hj. Abd. Manan Bin Hj. Samad, A/Professor Sr Hj. Muhammad Hj. Jaafar, Practical/Fieldwork Handout (2014). 3. Surveying For Engineers, J.Uren And W.F. Price, Third Edition, Levelling (1994). 4. Brian.Caulfield.Levelling,http://www.tcd.ie/civileng/Staff/Brian.Caulfield/3A1/3A1%20 Lecture%204.pdf. (retrieved 21 October 2014)

CONCLUSION As states in my hypothesis, we believe that we understand what are the purposes to do thetwo peg test is very important for surveyors, engineers and otherusers of land measuring 4

instruments, especially topographic appliances is important that allusers know the importance of permanent overlook of levels instrument, meaningchanges depending on the type how reading are taken and especially dependingon environmental conditions. At the end of a day, we have gain information about the two peg test should be carried out. We have learnt very important new things and discover how to check collimation error on the levels instrument. Not like before this, at that time, we never know the function of levels instrument and how it going to carried out and also not to forget how to check an error on levels instrument. But this time, we applied the knowledge that we gain to the instrument in front of our eyes. We know how to use it and the important things is, we know what the purposes of two peg test. The purpose and objective of all this activity is to make sure to check thelevels instrument is determine instrument collimation errors. If significant, corrections should be applied to levels reading that have been taken. A series of measurements on a base can also be used to check the performance and reliability of the instrument over time and to assess its precision against the manufacturer's specifications. Finally, we gain new knowledge, we studied new things, and the important things is, we know how to usethe instrument. We proud what we achieve, and hopes the things we learnt will be uses as good as possible and will be benefit others in the future.

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