Faculty of Applied Engineering and Urban Planning. Surveying. Civil Engineering Department. 2 nd Semester 2007/2008. Chain Surveying. Lecture 4. Content. Chain Surveying Sources of Errors Types of Errors. Errors. - No measurement (except count) can be free of error.
Civil Engineering Department
2nd Semester 2007/2008
There are many mistakes that cold be happened to surveyors.
- Blunders made by survey personnel
e.g. 68 instead of 86.
- Miscounting tape length, measuring from wrong point.
- Mistakes will occur and must be discovered and eliminated by verifying the measurement (Repeat Geometry analysis, etc.).
- Every measurement should be repeated to eliminate mistakes and improved precision.
Accuracy: relationship between measure & true value of measurement.
Precision: Degree of refinement with which the measurement is made.
True Distance Measured Distance Error
Cloth tape 157.22 157.3 0.08
Steel tape 157.22 157.23 0.01
- More precise method resulted in more accurate.
- More precise method may result in less accurate measurement.
Example: Repaired tape.
All standard in lengths
Tapes in lengths up to 100 ft
Some Taping Instruments
Along Baseline: stations
At right angle: offset dist.
Length AB = 4 x Full tape distance + 1 Short section
REMEMBER ! It works only on smooth ground or uniform slope surfaces
How about this very uneven case or high accuracy is required?
Sag curve measurement is not common nowadays and is restricted to steel tape only.
Prove Method 4 provided in the text book
Once a line is being measured, it is necessary to convert the measured length into a horizontal length. Series corrections have to be applied. Five possible corrections have to be considered. These are
When comparing to a standard tape, the tape used indeed has a length
30 m + ∆l
For every 30m measurement, the small elongated amount should be added for correction.
Angle may be measured by Theodolites
linear expansionTemperature Correction
horizontal length AB = 29.872-0.0050+0.0139-0.0022-0.0611+0.0052
Line Length Measured Slope Angle Mean Temp. Tension
AB 29.872 m 3o 40’ 5oC 120 N
The standardisation length of the tape against a reference tape was known to be 30.014 m at 20oC and 50 N.
If the tape weighs 0.17 N/m and has a cross sectional area of 2 mm2, calculate the horizontal length of AB.