According to RTU Syllabus

SURVEYING

Syllabus

LINEAR AND ANGULAR MEASUREMENTS

Part-3

Tapes

Types of tapes-

1.Cloth or linen tape-

• It is made up of closely woven linen and is varnished to resist the moisture.
• It is available in length of 10-30m and width of 12-15 mm.

Disadvantages of cloth or linen tape-

• It is affected by moisture and gets shrunk easily.
• Its length gets changed by stretching.
• It does not remain straight in strong winds and likely to twist.

2.Metallic tape-

• It is a linen tape with brass or copper wires woven into it.
• These are available in length of 20-30m.

3.Steel tape-

• It is more accurate than metallic tape.
• They are made up of steel.

4.Invar tape-

• These are made up of an alloy of nickel(36%) and steel(64%)
• These are available in length of 30,50 and 100m and width of 6mm.

Advantages of Invar tape-

• They have a very low coefficient of thermal expansion.so they are less affected by temperature changes.
• Highly precise.

Disadvantages of Invar tape-

• It is soft hence deforms easily.
• It can not be used for ordinary works.

Mistakes & Errors

Mistakes-

They are caused by carelessness or poor judgement.

ex-

• A reading of 10m is booked as 1m.
• Miscounting the no.of tape lengths. etc.

These can be revealed by taking the same measurement again with the same instrument.

Errors

• It does not arise due to mistake.

Errors are classified as-

1. Systematic error/Cumulative error
2. Random error/Accidental error/compensating error

Error = Measured value - True value

Correction = True value - Measured value

Systematic Error/Cumulative Error

• These Errors follow a definite mathematical or physical law.
• They are cumulative in nature.

          e.g.-

          Expansion of steel tape due to increase in temperature.

• These Errors can be checked by remeasuring the quantity by a different method using different instrument.

Random Error/Compensating Error/Accidental Error

• These are the Errors which remains after the mistakes and systematic errors are removed.
• They are random in nature.
• They are mainly caused by limitations of observer and instruments.

Aditi Sharma

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