Tape

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 Tape

Tapes is linear distance measuring instrument. Tapes are made of many materials and have the advantage of being light weight and providing greater precision. They cannot stand very rough handling as can chains. They can be divided into four classes according to the materials of which they made, such as follows:

  1. Cloth or linen tape
  2. Metallic tape
  3. Steel tape
  4. Invar tape

Cloth or linen Tape:

Tape made of cloth or linen can be termed as the cloth or linen tape. Generally this type of tapes used for the offset measurements. Due to their tendency to stretch easily, twist, and shrink when wet it is not used for the other measurements of high precision required. cloth tapes are available in lengths of 10m, 20m, 25m, 30m (10m to 30m) and in feet; 33ft., 50ft., 66ft., 100ft. One end of the tape is provided with small brass ring whose length is included in the total length of the tape.

Metallic Tape:
Metallic tape is made up of metallic wire provided with metallic ring. Since metallic tape is light in weight, flexible and not easily broken; they are particularly useful in cross-sectioning and in some methods of topography were small errors in length of the tape are of no consequence. It comes in the length of 2, 5, 10, 20, 30, and 50 m. The width of the tape is usually 16mm. Tape is suitably numbered and graduated to meters, decimeters, and centimeters. The tapes is usually supplied in the case and it can be rolled out for measurement.

Steel Tape:

Metric steel tapes can come in denominations of 1 to 50 m.  The tape is made of steel or stainless steel  and can have a protective vinyl coating to prevent from rusting. The tape has a metallic ring at the outer end , which is fastened with a metal strip of the same width of tape. A steel tape consists of light strip of width 6 to 10 mm. Steel tape is costly compared to the former types of the tapes but is a very accurate distance measuring instrument. The length of the tape includes the metal ring.
the tape is suitably numbered and graduated to m, dm, cm, and mm. The tape comes in a suitable case and can be pulled out to the required length with the metallic ring. The tape wind back automatically when a button on the case is pressed. The steel tape should be preferred for the precision work in distance measurement.

Invar Tape:
Invar tape is made  of an alloy of steel(64%) and nickel(36%) and is used for very high precision work, as in base line measurement for triangulation. Invar tape has very low coefficient of thermal expansion; seldom more than about one- tenth of that of steel. It comes in length of 30m, 50m, and 100m and is about 6 mm wide. It is very delicate requiring careful handling and is hence used for high precision work only. Invar tapes and bands are more expensive, much softer and more easily deformed than steel tape.
Another great disadvantage of invar tape is that it is subjected to creep due to which it undergoes a small increase in length as time goes on. Its coefficient   
 

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