Wednesday, February 19, 2014

Traditional survey - chain survey-01

Chain

The chain is a instrument and unit, using for surveying and measure distances. The chains used in surveying are generally of the following types.
I. Gunter’s chain
II. Engineer’s chain
III. Metric chain
IV. Steel Band Chain
V. Revenue Chain

         




I. Gunter’s chain
surveyor’s chain, also called Gunter’s chain, measuring device and arbitrary measurement unit still widely used for surveying in English-speaking countries. Invented by the English mathematician Edmund Gunter in the early 17th century, Gunter’s chain is exactly 22 yards (about 20 m) long and divided into 100 links. In the device, each link is a solid bar. Measurement of the public land systems of the United States and Canada is based on Gunter’s chain. An area of 10 square chains is equal to one acre.
II. Engineer’s chain
This steel engineers’ chain would have been used by a surveyor measuring out lands and plot sizes.  It is different from a surveyor’s chain as it is larger in length however it would have been used for the same purpose, measuring out horizontal distances.  The chain measures 100 ft and contains 100 links, each measuring 12 inches.  The links each consist of a thin round steel rod joined with an oval ring on each end.  Tags mark the chain at every ten links.  It was made by W. & L.E. Gurley of Troy, New York.  Brothers William Gurley and Lewis formed the company in 1852; they were both graduates of Rensselaer Polytechnic Institute in New York.

III. Metric chain
A metric chain is generally divided into 100 or 150 links. The links are composed of pieces of galvanized mild steel wire 4mm in diameter. The ends of each link are bent into loops and connected together by means of three oval shaped rings which afford the flexibility to the chain. The joints of the links are usually pen but in good quality chains, these are welded so that true length of the chain does not alter due to stretching. The ends of the chain are provided with brass handles with swivel joints so that the chain can be turned round without twisting. The outside of the handle is the zero point or the end point of the chain. The length of a chain is measured from the outside of one handle to the outside of the other. The length of a link is the distance between the centers of the two consecutive middle rings. The end links also include the length of the handle. Metallic tags of different patterns are fixed at various important points of c chain.

IV. Steel Band Chain
It consists of a ribbon of steel with bras handle at each end. It is 20 or 30 long and 16 mm wide. It is wound on an open steel cross or on the metal reel in a closed case. The graduations are etched as meters decimeters, centimeters on one side and 0.2 m links on the other. Brass tallies are fixed at every 5 m length of the band.
V. Revenue Chain
It is commonly used for measuring fields in cadastral survey. It is 33 ft long and divided into 16 links. Each link is 2.0625 ft long.

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