COMPLETE NOTES ON DECECChapter-02_1.pptx

COMPLETE NOTES ON DECECChapter-02_1.pptx

1. Chapter-02 Measurements & Errors 2.1 Units, System of Units, Significant figures and rounding off numbers 2.2 Errors, Sources & Types 2.3 Precision, Accuracy & permissible error

2. 2.1 Units, System of Units, Significant figures and rounding off numbers Linear Measurement Metric System/SI system FPS System (British Engineering System ) Length in meter (m) Length in Foot (ft.) Mass in Kilogram (Kg) Mass in Pound (lb) Time in Second (s) Time in second (s)

3. Angular Measurement: Sexagesimal System (English system) degrees, minutes, seconds Centesimal System (French System) grade, minutes, seconds 1 right angle = 100 grades 1 grades = 100 minutes 1 minutes = 100 seconds 3. Circular System ( radians ) A radian is an angle subtended at the center of a circle by an arc whose length is equal to the radius. radians =degree ∗ ( PI /180) 90° = π/2 rad, 180° = π rad, 360° = 2π rad 2.1 Units, System of Units, Significant figures and rounding off numbers

4. 2.1 Units, System of Units, Significant figures and rounding off numbers Ropani Aana 16 Bigha Paisa 4 64 Kattha 20 Daam 4 16 256 Dhur 20 400 1.99 m 2 7.95 m 2 31.80 m 2 508.74 m 2 16.93 m 2 338.63 m 2 6772.63 m 2 21.39 ft 2 85.56 ft 2 342.25 ft 2 5476 ft 2 182.25 ft 2 3645 ft 2 72900 ft 2

5. 2.2 Errors, Sources & Types Error in an observation is the difference between a measured value of a quantity and the true value of that quantity. Error = Measured Value – T ru e Value Types of Errors Mistakes/Blunders Systematic errors Random errors/Accidental error

6. 2.2 Errors, Sources & Types A. Mistakes/Blunders Mistakes or blunders are unpredictable human mistakes caused due to carelessness, misunderstanding, confusion or poor judgment. Mistakes can be avoided by alertness, common sense and good judgment. Common types of M istakes/Blunders are: Transposition of numbers Neglecting to level an instrument Misplacing decimal point Sighting on incorrect control point

7. 2.2 Errors, Sources & Types B. Systematic Errors Systematic error is such type of error which have same magnitude and the same algebraic sign under the same conditions. In most cases, systematic errors are caused by physical and natural conditions that vary in accordance with fixed mathematical and physical laws. Systematic errors are cumulative in nature. can be minimized by procedural changes such as standardizing the tapes, balancing of sights etc. corrections must be applied to measurements. Common examples of systematic errors are: Thermal contractions or expansion of steel tape. Incorrect length of a level rods and staff. Curvature and refractions. Incorrect prism constant on a total station etc.

8. 2.2 Errors, Sources & Types C. Random Errors Random errors are also called Accidental errors, which do not follow any fixed relation to the conditions of observations. Random errors obey the laws of chance and are analyzed by the laws of probability. Theoretically, random errors have an equal chance of being negative or positive. Thus, errors of this type tend to be compensating. Can be minimized by repeating the measurements .

9. 2.2 Errors, Sources & Types Sources of Errors Personal Errors Personal errors are caused by physical limitations and observing habits of an observer . They can be either systematic or random. Instrumental Errors Instrumental errors are caused by the imperfections in the design, construction, and adjustment of instruments and other accessories. Most instrumental errors are eliminated by using proper procedures such as observing angles direct and reverse, balancing foresights and back sights and repeating measurements. M inimized by periodically checking and adjusting (or calibrating) instruments and other equipment. Example: Wrong calibration in the tape or staff. Wrong calibration of EDM Bubble out problem in level, theodolite

10. 2.2 Errors, Sources & Types Sources of Errors….. from natural temperature , physical humidity, conditions gravity, wind such as and Natural Errors Natural errors result atmospheric pressure , atmospheric refraction. Natural errors are removed from a measurement by determining corresponding corrections from known relationships between an error and the related natural phenomena.

11. 2.2 Errors, Sources & Types COMMON MISTAKES IN CHAINING/TAPPING: Displacement of the arrows. Failure to observe the zero point of the tape. Reading from the wrong end of the chain /tape . Reading numbers wrongly/ Reading wrong meter marks . Wrong recording in the field book. Calling numbers wrongly.

12. 2.3 Precision, Accuracy & permissible error Accuracy: Accuracy is defined as ‘The degree of closeness with the ‘standard value’ and essentially refers to how close a measurement is to its agreed value. Degree of perfection obtained in the measurement. Precision: Precision refers to closeness of two or more measurements to each other. P recision indicates the level of detail, refinement, or granularity in the measurement.

13. 2.3 Precision, Accuracy & Permissible error

14. 2.3 Precision, Accuracy & permissible error Discrepancy: is the difference between two measured values of the same quantity . Discrepancy may be small, yet the errors can be large if both the observed values contain almost equal error. Error: in an observation is the difference between a measured value of a quantity and the true value of that quantity. Error = Measured Value – T r u e Value

15. 2.3 Precision, Accuracy & permissible error Q . In angular measurement of a triangle ABC, the internal angles are found  A= 60  30  ,  B= 45  20  ,  C= 75  3  . Calculate the error in measurement and accuracy of the work.

16. 2.3 Precision, Accuracy & permissible error Q . In angular measurement of a triangle ABC, the internal angles are found  A= 60  30  ,  B= 45  20  ,  C= 75  3  . Calculate the error in measurement and accuracy of the work.

17. 2.3 Precision, Accuracy & permissible error

18. 2.3 Precision, Accuracy & permissible error

19. 2.3 Precision, Accuracy & permissible error Permissible error: Refers to the acceptable level of error or tolerance allowed in the measurement of survey data. The specific permissible error varies depending on the type of survey, the purpose of the survey, and the accuracy requirements of the project. Different surveying applications may have different permissible error standards.

20. Assignments Make a proper note of this Chapter in your note copy

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