Wednesday, February 19, 2014

survey instruments 01-Tapes

Tapes




Tapes are used in surveying to measure horizontal, vertical, and slope distances. They may be made of a ribbon or a band of steel, an alloy of steel, cloth reinforced with metal or synthetic materials. Tapes are issued in various lengths and widths and graduated in a variety of ways.
I. Cloth or Linen Tape
II. Metric Woven Metallic Tape
III. Metric Steel Tape
IV. Invar Tape
V. Synthetic Tape


I. Cloth or Linen Tape
It is made of varnished strip of woven linen 12 to 16 mm wide with a brass handle at zero ends, whose length is also included in the length of the tape. The tape is attached to a spindle and is wound in a leather case. It is very light and handy, but not so accurate. For very precise measurements, it is not used. The linen tape may be used for taking subsidiary measurements such as offsets. It is easily affected by damp. When the tape gets wet, it shrinks and care should be taken that it is not wound up until is cleaned and dried. It stretches easily and is likely to twist and tangle. It is therefore little used in surveying.

II. Metric Woven Metallic Tape
They are available in 2, 10, 30, and 50 meters. The tape is made of yarn and metal wire. A metal ring is attached to the outer end of tapes. The length of the tape includes the metal ring. At every centimeter a black line 8 to 10 mm in height is drown. Every 5 centimeters is marked with an arrow in black. Every decimeter and meter is marked with a back line extending over the full width of the tape the graduation marks at every decimeter and meter are numbered with black and red figures, respectively.

III. Metric Steel Tape
Tape is available in 1, 2, 10, 30, and 50 meters. The tape is of steel or stainless steel. The outer end is provided with a ring. The length of the tape includes the metal ring. The tape is marked with a line at every five millimeters, centimeters, decimeters, and meter. Every decimeter and meter shall be marked with Hindu Arabic numerals in bold. When the button release devised is pressed, the tape automatically rewind in to the case.

IV. Invar Tape
For highest precision work the invar tape in used. Invar tapes are made of an alloy of nickel (36%) and steel (64%) having very low co-efficient of thermal expansion (0.000000122 per 1 C) These are 6mm wide and are available in length of 30m, 50m and 100m, Invar taps are used mainly for high degree of prevision required for base measurements.

V. Synthetic Tape
The tapes are manufactured of glass glass fiber having PVC coating. They are graduated every 10 mm and figured every 100 mm. Meter, figures are shown in red. They are convenient for measuring shorts lengths.

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