Plane Table Surveying Techniques

Two-Peg Method

• Used to adjust dumpy levels for accurate leveling
• Involves taking readings on two pegs at known distances
• Adjusts the level by adjusting the bubble and ensuring the line of sight is horizontal
• Uses precise measurements with readings at different positions to ensure accuracy
• Important for determining the height of points above a datum

Plane Table Accessories

• Plane Table: Base for drawing and plotting survey data
• Alidade: Used for sighting and measuring angles
• Spirit Level: Ensures the plane table is level for accurate measurements
• Drawing Instruments: Used for plotting data on the plane table sheet
• T-Square: Ensures straight lines when plotting
• Ruling Pen: Used for drawing lines
• Beacons: Used to mark specific points in the field
• Plumbing Fork: Used to accurately center the plane table over a point
• Jacob's Staff: Used to locate points from the plane table

Plane Table Surveying Methods

• Radiation Method: Used to establish the location of points with respect to a known point by radiating lines from the plane table
• Intersection Method: Determines the location of a point by intersection of lines of sight from two known points
• Traversing Method: Determines the location of consecutive points with respect to each other
• Resection Method: Uses three or more known points to locate the position of the plane table
• Triangulation Method: Determines the location of points using triangles

Advantages of Plane Table Surveying

• Direct Plotting: Drawing the survey data directly on the plane table
• Flexibility: Can be used in various terrains and conditions
• Immediate Results: Provides instant visual representation of the survey
• Relatively Inexpensive: Compared to other surveying techniques

Purpose of Leveling

• To determine the difference in height between two or more points
• Used to establish benchmarks and determine elevation
• Essential in various applications including construction, surveying, and engineering

Check Leveling

• Check leveling: A method to verify the accuracy of the levelling process
• Involves establishing a closed circuit of leveling
• Method: The level is set up at different locations and readings are taken on the same point at the beginning and end of the circuit
• If the difference in readings is within acceptable limits the leveling is accurate

Traverse Bearings & Station Attraction

• Attraction: Magnetic attraction can affect the accuracy of the bearings
• This will affect the bearings measured at a specific station
• Determining Affected Stations: Compare the F.B. and B. Bearings for each line
• The station that has a significant difference in the readings is likely affected by attraction
• Correcting Bearings: The correct bearings need to be determined by adjusting for magnetic attraction
• This can be done using magnetic declination values and appropriate formulas

Reduced Levels & Instrument Method

• Reduced Level (RL): The height of a point above a datum
• Instrument Method: Used to calculate RLs
• Begins by taking a reading on a bench mark (known RL)
• The instrument height (IH) is calculated by adding the BM RL to the first reading
• Subsequent RLs are calculated by subtracting each reading from the current IH
• Table: | Reading | IH | RL | |---|---|---| | 2.22 | 434.60 | 432.38 | | 0.988 | 434.60 | 433.61 | | 2.090 | 434.60 | 432.51 | | 2.864 | 434.60 | 431.74 | | 1.262 | 433.34 | 432.08 | | 0.602 | 433.34 | 432.74 | | 1.98 | 432.74 | 430.76 | | 2.684 | 432.74 | 430.06 |

Two-point Problem

• Two-point problem: Used to determine the position of a point when two known points are visible
• Method:
  1. Plot the known points on the plane table sheet.
  2. Sight the first known point using the alidade.
  3. Draw a line on the plane table sheet, passing through the plotted point.
  4. Sight the second known point and draw a line passing through the second plotted point.
  5. The intersection of the two lines is the position of the unknown point.
• Applications: This method can be used to establish the position of a point for surveying or mapping purposes

Transformer Oil Properties

• Impact of Oil Properties: The quality of transformer oil is crucial for proper operation and preventing damage.
• Moisture: Moisture contamination in transformer oil can cause insulation failure and affect the effective functioning of the transformer.
• Gases: Presence of gases in the transformer oil can indicate internal faults and degradation of the insulating materials.
• Dielectric Strength: The ability of the oil to withstand electric stress and prevent short circuits.
• Viscosity: The resistance of the oil to flow, which affects the cooling efficiency of the transformer.

Explore the essentials of Plane Table Surveying, focusing on the Two-Peg Method and important accessories. This quiz covers the use of equipment such as the alidade and spirit level, along with methods to ensure accurate leveling and plotting of survey data. Test your knowledge on how these tools contribute to precise measurements in surveying.