Instruments Used in Chain Surveying

Chain surveying is a traditional method of land surveying that involves the measurement of distances and angles using a chain or a tape measure along with other instruments. This method is widely used for small and medium-scale surveys where high accuracy is not required. Here's a detailed note on the instruments used in chain surveying:

1. Measuring Chain or Tape: The measuring chain or tape is the primary instrument used for measuring distances between survey points. It consists of a series of connected links or a flexible tape marked at regular intervals (usually in meters or feet). Chains are typically made of steel, while tapes can be made of steel, fiberglass, or other materials. The standard length of a chain is 20 meters (66 feet), and a tape may vary in length according to requirements.

   

2. Ranging Rods: Ranging rods are used to mark survey points and to provide a target for sighting when measuring distances. They are typically made of wood or metal and painted in bright colors for easy visibility. Ranging rods are placed vertically at survey points or along the survey line.

   

3. Cross Staff: The cross staff is used to set right angles during surveying. It consists of two arms perpendicular to each other, one of which is movable. The cross staff is placed at the starting point of a survey line, and the movable arm is aligned with a reference line (e.g., a plumb line) to ensure perpendicularity.

   

4. Arrows and Flags: Arrows or flags are attached to ranging rods to provide a clear target for sighting. They are usually brightly colored and can be easily seen from a distance. Arrows are used for marking points in open areas, while flags are used in dense vegetation or on uneven terrain.

   

5. Plumb Bob: A plumb bob is used to ensure that ranging rods are positioned vertically. It consists of a pointed weight attached to a string or wire. When the plumb bob is suspended from the top of a ranging rod, it indicates the true vertical line, allowing for accurate positioning of the rod.

   

6. Offset Rod: An offset rod is used to measure perpendicular distances from the survey line to objects or features of interest, such as buildings, fences, or trees. It is similar to a ranging rod but is equipped with a sliding bracket or hook for accurate measurements.

   

These instruments are essential for conducting chain surveying accurately and efficiently. They enable surveyors to measure distances, set right angles, mark survey points, and record field observations with precision. Proper care and calibration of these instruments are necessary to ensure reliable survey results.