The Constructor

Types of Chains used in Surveying, Their Parts, Testing and Advantages

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Chains are the measuring instrument used in surveying formed by the 100 links of 4mm galvanized mild steel wire. These links are joined by 3 circular or oval wire rings. These rings provide the flexibility to the chains. Every aspect of the life requires some measuring units. Measurements are used to do the work precisely and accurately. Let it be from kitchen to office, everywhere measurements are used. So as in engineering calculation or measurements holds a very greater role in construction or surveying or any other aspect. There are various units of measurements such as meters, centimeters, feets, inches, acre, yards and the list goes on. Same as units there are various instrument used in the measurements of any entity. One of the instruments used in measurement are chains.

Parts of Chains used in Surveying

The chain consists of many small parts used for handling or reading the measurements.

Types of Chains used in Surveying

Depending upon the length of the chain, these are divide into following types,
  1. Metric chains
  2. Steel band or Band chain
  3. Gunter's chain or surveyor’s chain
  4. Engineer’s chain
  5. Revenue chain

A. Metric chains

Metric chains are the most commonly used chain in India. These types of chains comes in many lengths such as 5, 10, 20 and 30 meters. Most commonly used is 20m chain. Tallies are provided at every 2m of the chain for quick reading. Every link of this type of chain is 0.2m. The total length of the chain is marked on the brass handle at the ends.

B. Steel band or Band chain

These types of chain consist of a long narrow strip of steel of uniform width of 12 to 16 mm and thickness of 0.3 to 0.6 mm. this chain is divides by brass studs at every 20cm or instead of brass studs, band chain may have graduated engraving as centimeter. For easy use and workability band chains are wound on steel crosses or metal reels from which they can be easily unrolled. These steel bands are available in 20m and 30m length and the width of about 12-16mm.

C. Gunter's chain or surveyor’s chain

Gunter chain comes in standard 66ft. These chain consists of 100links, each link being 0.66ft or 7.92inches. The length 66ft is selected because it is convenient in land measurements. 10 square Gunter’s chains = 1 Acre 10 Gunter chains = 1 Furlong 80 Gunter chains = 1 mile

D. Engineer’s chain

This chain comes in 100ft length. Its consist of 100 links each link being 1ft long. At every 10 links a brass ring or tags are provided for indication of 10 links. Readings are taken in feet and decimal.

E. Revenue Chain

The standard size of this type of chain is 33ft. The number of links are 16, each link being 2 ft. This chain is commonly used in cadastral survey.

Testing and Adjustment of Chain

As the chain is a metal made, it may undergo many changes due to temperature effect or human error and etc. So for all lengths of chain a tolerance is given, 5m chain = + or – 3mm 10m chain = + or – 3mm 20m chain = + or – 5mm 30m chain = + or – 8mm

Chain length shorten due to

  1. Bending of links.
  2. Sticking of mud in the rings

Chain length increases due to

Chains may be tested with respect to

If chain is found long, then

If chain is found short, then

Errors in chain Surveying

Errors in chaining may be classified as:

Personal Errors

Wrong reading, wrong recording, reading from wrong end of chain etc., are personal errors. These errors are serious errors and cannot be detected easily. Care should be taken to avoid such errors.

Compensating Errors

These errors may be sometimes positive and sometimes negative. Hence They are likely to get compensated when large number of readings are taken. The magnitude of such errors can be estimated by theory of probability. The following are the examples of such errors:

Cumulative Errors

The errors that occur always in the same direction are called cumulative errors. In each reading the error may be small, but when large number of measurements are made they may be considerable, since the error is always on one side. Examples of such errors are:
  1. Bad ranging
  2. Bad straightening
  3. Erroneous length of chain
  4. Temperature variation
  5. Variation in applied pull
  6. Non-horizontality
  7. Sag in the chain, if suspended for measuring horizontal distance on a sloping ground.
Errors (i), (ii), (vi) and (vii) are always +ve since they make measured length more than actual.

Advantages and Disadvantages of Chains in Surveying

Advantages of Chains in Surveying

Disadvantages of Chains in Surveying

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