[PPT4] Tape Corrections

Question 1

RULES IN TAPE CORRECTIONS

Answer 1

First Rule: When a line is measured with a tape that is
“TOO LONG”, corrections are ADDED

Second Rule: When laying out a length with a tape that is “TOO LONG”, corrections are SUBTRACTED

Third Rule: When a line is measured or laid out with a tape that is “TOO SHORT”, corrections applied are opposite of 1st and 2nd rules

Question 2

GENERAL STATEMENT

Answer 2

“When measuring with tape TOO LONG, ADD; TOO SHORT, SUBTRACT. Do the reverse when laying out.”

Question 3

CORRECTIONS TO TAPE

Answer 3

1. Due to Tape Not of Standard Length
2. Due to Slope
3. Due to Alignment
4. Due to Temperature
5. Due to Tension
6. Due to Sag
7. Due to Wind

Question 4

1. TAPE NOT OF STANDARD LENGTH

Answer 4

• Often due to imperfections in their manufacture, stretching or wear
• Also due to constant use of tapes becoming worn, kinked, and improperly repaired when breaks occurred.
• Corrections may vary from few millimeters or centimeters

Question 5

CORRECTION PER TAPE LENGTH

Answer 5

Corr = TL - ML

Corr - correction per tape length
TL - true length
ML - measured length

Question 6

CORRECTED LENGTH TO BE MEASURED

Answer 6

CL = ML ± Corr(ML/NL)

CL - corrected length of the line to be measured or laid out
ML - length measured or laid out
Corr - correction per tape length (TL - ML)
TL - true length
NL - nominal length of tape

Question 6

CORRECTED LENGTH TO BE MEASURED

Answer 6

CL = ML ± Corr(ML/NL)

CL - corrected length of the line to be measured or laid out
ML - length measured or laid out
Corr - correction per tape length (TL - ML)
TL - true length
NL - nominal length of tape

Question 6

CORRECTED LENGTH TO BE MEASURED

Answer 6

CL = ML ± Corr(ML/NL)

CL - corrected length of the line to be measured or laid out
ML - length measured or laid out
Corr - correction per tape length (TL - ML)
TL - true length
NL - nominal length of tape

Question 7

CORRECTED LENGTH TO BE MEASURED

Answer 7

CL = ML ± Corr(ML/NL)

CL - corrected length of the line to be measured or laid out
ML - length measured or laid out
Corr - correction per tape length (TL - ML)
TL - true length
NL - nominal length of tape

Question 8

2. DUE TO SLOPE

Answer 8

When distances are measured along a slope, the equivalent horizontal distance may correspondingly be determined by applying an approximate or exact slope correction

Question 9

3. DUE TO ALIGNMENT

Answer 9

• Linear error due to inaccuracy in alignment of a tape
• Similar to the effect of slope
• Easier to control and smaller in magnitude
• Generally least important among different tape corrections

Question 10

4. DUE TO TEMPERATURE

Answer 10

• Change in the length of the tape due to variations in temperature
• Occurs when measurements are taken at temperatures above or below the standard temperature of the tape
• Correction is usually small and negligible
• Proportional to the number of tape lengths

Question 11

5. DUE TO TENSION

Answer 11

• Arises whenever the pull applied is different from the standard tension used in calibration

A function of:
* Difference between applied and standard pulls
* Measured length
* Cross-sectional area of the tape
* Modulus of elasticity of the tape material

Question 12

6. DUE TO SAG

Answer 12

• Occurs when tape supports are only at its ends or at the 2 points measured
• Will sag because of its own weight
• Similar to electric or telephone wires which swings loosely between two posts

Question 13

7. DUE TO WIND

Answer 13

• Caused by wind blowing perpendicular to the direction of taping
• Wind moves the middle and unsupported portion of the tape to one side of the line measured
• Similar to the effect of sag but is usually much less
• Preferable not to undertake any taping work during windy days