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Which of the following causes an increase or decrease in chain length?
Stretching of the links and joints
Opening out of the rings
Wearing of rings
All of the above
All of the above
In surveying, the chain length is defined as the distance between the outside of the handles ┬╖ Physical factors like mechanical strain, wear and tear at the joints, and the deformation of the circular rings lead to permanent changes, causing the chain to become either too long or too short.
In surveying, the chain length is defined as the distance between the outside of the handles ┬╖ Physical factors like mechanical strain, wear and tear at the joints, and the deformation of the circular rings lead to permanent changes, causing the chain to become either too long or too short.
LtrueтАЛ=LmeasuredтАЛ├ЧLnominalтАЛLincorrectтАЛтАЛ тАФ Correction formula for a chain of incorrect length
The chain is composed of multiple links connected by small rings ┬╖ Stretching occurs due to excessive pulling (tensile force) beyond the elastic limit of the material ┬╖ Opening out of rings occurs when the circular geometry deforms into an elliptical shape under tension ┬╖ Wearing of rings reduces the diameter of the contact points due to friction with the ground, primarily causing the chain to elongate.
A chain is considered correct if its length is equal to the nominal length at a specified temperature (usually 20┬░C) and pull.
Elongation of the chain leads to a negative error in measurement, while contraction leads to a positive error.
Regular testing against a standard tape or base line is mandatory to identify these errors.
Kinking and bending of links are other common causes of physical length changes in surveying chains.
High durability and robust construction suitable for rough terrain.
Easy to repair in the field using spare links.
Heavy weight compared to metallic tapes.
Susceptible to physical wear and deformation over time.
Length changes due to temperature variations (thermal expansion/contraction).
Rough field surveying where high precision is not required.
Educational training for basic chain surveying techniques.
Standard chains like the Gunter's chain (66 ft) or Metric chain (20m/30m) are highly prone to these errors.
Option B (Opening out of rings) is a primary cause of lengthening, whereas Option C (Wearing of rings) can also lead to elongation due to the smoothing of contact surfaces.
D is correct тАФ Stretching, opening of rings, and wearing of joints all alter the physical geometry of the chain, thereby changing its total effective length.
Always remember: If the chain is too long, the measured distance is less than the true distance (negative error); if the chain is too short, the measured distance is more than the true distance (positive error).