Tape Corrections
- By means of steel tapes, the precise measurements were made having a steep tape length 30 m or 50 m in length.
- The steel tape use, it is desirable to ascertain its absolute length or actual length by comparing it with the standard length, which can be done standard department or may check by small fee by the survey.
- The distinction between the designated and nominal length at any absolute length of steel tape.
- When supported horizontally the tape may be standardized throughout its full length.
- At a standard temperature it is the expression that tape is standard and with a certain pull, under these all conditions, the actual length of the steel tape is exactly equal to its nominal length.
Under those standard conditions, the tape is not used in the field it is very necessary to apply the following corrections which are written below in order you want to get true length:
1. Correction for absolute length.
Ca = Lc/l
2. Correction for temperature.
Where
Ct = the correction for temperature, in m.
a = the coefficient of thermal expansion.
Tm = the mean temperature during measurement.
To = the temperature at which the tape is standardized.
L = the measure length in m.
3. Correction for tension or pull.
4. Correction for sag.
Cs = − (wL ) ^2 x L / 24 P^2
Where,
Cs = Sag correction in meters for length (l)
l = the length of the tape (in meters)
P = Pull applied in kg or N
W = weight of the tape in kg or N per meter run
wL = weight of tape suspended between the supports.
- Sag correction is directly proportional to the square of the weight of the tape (kg/meter )
- Sag correction is always Negative (-VE)
- Sag correction is inversely proportional to the pull applied
5. Correction for slop or vertical alignment.
Ch = d2/2L
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