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linear_measurementS IN METROLOGY & INSTRUMENTATION
- 2. METHODS OF LINEAR MEASUREMNENT APPROXIMATE METHODS CHAIN SURVEYING CHAIN TAPES RANGING RODS METHODS USED IN CHAIN SURVEYING PRINCIPLE OF CHAIN SURVEYING SELECTION OF CHAIN SURVEYING OFFSETS ERRORS TYPES OF ERRORS SOURCE OF ERRORS
- 3. There are 3 methods of making linear measurements. 1- Direct Method. 2- Optical Method. 3- E.D.M Method.
- 4. Pacing. Passometer. Pedometer. Odometer. Speedometer. Measuring Wheel.
- 6. 1) Chains 2) Tapes 3) Arrows 4) Ranging Rods and Offset Rod 5) Pegs 6) Plumb- bob
- 7. Metric chain Gunters chain or Surveyors chain Engineers chain Revenue chain Steel band or Band chain
- 9. TAKING MEASUREMENTS ON CHAIN TAKING MEASUREMENTS ON CHAIN Metric chains are made in lengths 20m and 30m. Tallies are fixed at every five-meter length and brass rings are provided at every meter length except where tallies are attached.
- 10. If chain is found to be too long If chain is found to be too short 1) 1) Closing up the joints of the Closing up the joints of the rings if found to be opened out. rings if found to be opened out. 2) 2) Reshaping the elongated rings. Reshaping the elongated rings. 3) 3) Replacing damaged rings. Replacing damaged rings. 4) 4) Removing one or more small Removing one or more small rings. rings. 5) 5) Adjusting the links at the end. Adjusting the links at the end. 1) 1) Straightening the bent links. Straightening the bent links. 2) 2) Opening the joints of the rings. Opening the joints of the rings. 3) 3) Replacing one or more small Replacing one or more small circular rings by bigger ones. circular rings by bigger ones. 4) 4) Inserting new rings where Inserting new rings where necessary. necessary. 5) 5) Adjusting the links at the end. Adjusting the links at the end.
- 11. 1) Cloth or linen tape. 2) Fibre tape. 3) Metallic tape. 4) Steel tape. 5) Invar tape.
- 13. Arrows are made of tempered steel wire of diameter 4mm. One end of the arrow is bent into a ring of diameter 50mm and the other end is pointed. Its overall length is 400mm. An arrow is inserted into the ground after every chain measured on the ground.
- 14. Ranging rods are 2 to 3 m in length. Used for ranging some intermediate points on the survey line. Painted with alternate bands of black and white or red and white colours. With length of each equalising 20 cm.
- 16. Made of timber or steel. Used to mark the position of stations. Pegs are in length of 15 cm.
- 17. Used to transfer points on ground. Used for fixing instrument exactly over the stations.
- 18. Triangulation is the principle. In this area is divided into a number of triangles with the suitable sides. The plan of the area can be easily drawn. As a triangle is the only simple plane geometrical figure.
- 19. 1) Survey Stations: (a) Main stations (b) Subsidiary stations (c) tie stations 2) Main survey lines 3) Base line 4) Check line 5) Tie-line
- 21. 1) Survey lines should be minimum as far as possible and should be taken on fairly level ground. 2) should be intervisible. 3) Should form well conditioned triangles. 4) Should be located that tie lines, check lines, baseline etc. an be formed. 5) Should be selected within the boundary of the area to be surveyed.
- 22. Chaining Ranging Offsetting
- 23. Chaining on level ground It involves following operations 1) Fixing the stations. 2) Unfolding the chain. 3) Ranging. 4) Measuring the distance. 5) Folding the chain.
- 24. There are 2 methods: Direct Method: Also called as stepping. In this method, the distance is measured in small horizontal stretches. Say a1, a2 an. with suitable length of chain or tape. finally the total horizontal distances are added to get the required distances
- 25. w x y z c b a
- 27. It involves calculation from directly measured lengths. Method1: Horizontal distance of the segment is calculated by knowing sloping length of the segment and angle of inclination of that with horizontal. The angle of the sloping surface with horizontal can be known by instrument called Clinometer.
- 28. If the elevation difference between 2 terminals points and the sloping distance between 2 terminal points is known the horizontal distance D can be calculated as D = (l族-足 h族)
- 29. Also called as hypotenusal allowance method Instead of putting the end arrow at actual end of chain, it is put at some advanced distance and that point is considered as the end of one chain length
- 30. There are 2 methods: 1) Direct ranging 2) Indirect ranging or reciprocal ranging.
- 31. When intermediate ranging rods are fixed on a straight line by direct observation from end stations, the process is known as direct ranging. Direct ranging also can be done with a line ranger it consist of 2 right isosceles triangular prisms. Placed one above other.
- 33. When the end stations are not intervisible due to there being high ground between them, intermediate ranging rods are fixed on the line in an indirect way. The method is known as indirect ranging or reciprocal ranging.
- 34. Indirect Ranging
- 35. There are 2 types of offsets: 1) Perpendicular offsets: the offsets which are taken perpendicular to the chain are termed as above. 2) Oblique offsets: Oblique distance is always greater than perpendicular distance. All the offsets which are not taken at right angle to chain line are known as above.
- 36. Optical square. Indian optical square. Open cross staff. Prism square.
- 37. There are 2 types 1) Compensating errors 2) Cumulating errors
- 38. Instrumental Errors Natural errors Personal errors
- 39. If chain is too long If chain is too small Measured distance will be less. Correction: positive Measured distance will be more. Correction: negative
- 40. Corrections for absolute length Corrections for temperature Corrections for pull Corrections for sag Corrections for slope