03_Levelling - Levelling Use of an optical level to...

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Levelling Use of an optical level to determine height differences, and to establish marks at defined heights.
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This Lecture will Cover • Instrumentation and levelling procedure • Sources of error in the measurement process and means of reducing error. • The use of levelling to determine heights and application within the production of survey plans. • The use of levelling to establish marks at given heights for construction purposes. • Use of levels to construct cross sections.
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Part 1 The Optical Tilting Level and its use.
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Optical Level TELESCOPE View Pivot Bubble Tripod Mounting Levelling screws
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Levelling Measurements Staff Staff Level Fore sight Back sight A B 9.4 m 5.1 m If the accepted height of point A is 153.824 m what is the height of B?
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Questions • Does it matter where the level is located? • What precaution must be taken in holding the staff?
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Holding the staff
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Instrument Error Pivot Bubble Levelling screws View Bubble level Line of sight Collimation error.
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Instrument Test 10 m 10 m 10 m Peg 1 Peg 2 Setup A Setup B h A1 h A2 h B1 h B2 Two peg test.
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Collimation Example Observations made at A are: h A1 1.500m and h A2 0.500m The true height difference ( h) between peg 1 and peg 2 is 1.000m. Observations made at B are: h B1 3.500m and h B2 2.000m a height difference ( h) of 1.500m The fact that the values for h are different suggests that there is a collimation error present in the instrument. The values used are exaggerated Up to 3mm over the 30m distance is normally acceptable.
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• How much collimation error exists in the instrument? Hint: describe this in terms of mm vertical
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This note was uploaded on 03/25/2012 for the course CIVIL 201 taught by Professor Keithmiller during the Spring '12 term at Acton School of Business.

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03_Levelling - Levelling Use of an optical level to...

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