Therefore we have to apply corrections to get the true result. Since the effect of the set on the tapes is to make the measured length too great this correction is always, Temperature correction per tape length = C, Correction per tape length = α ( (T, Pull correction per tape length = (P, Correction for sag = C, ~ Corrected length of the tape =, ~ The required correction = 0.8, Correction for incorrect alignment = d, UG Courses - Agricultural Engineering (Version 2.0). 2) Locating various objects by chain & cross staff surveying. This document is highly rated by Agricultural Engineering students and has been viewed 3538 times. This is most suitably adapted to small plane areas with very few details. Where Ca = the correction for absolute length. Introduction to principle of surveying 2. If l is the length of any one slope, and h the difference in height between the ends of the slope, = l – l (1 – h2 / 2l2 – h4 / 3l4 – etc..), =(h2 / 2l + h4 / 3l3 + etc.) After participating in this fieldwork students will become more comfortable with handling chain and ranging rods. If not, we need next to determine if the error i… The value of Pn may be determined by trial. <>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 612 792] /Contents 4 0 R/Group<>/Tabs/S>> Linear measurement In engineering survey, the linear horizontal distance is to be measured to complete a survey. It is given by the formula, Cs = l1 (mgl1)2 / 24P2 = l1(Mg)2 / 24P2 ………………(4). P = the pull applied during measurement, in newtons (N). This is suitable for the survey of small areas with simple details and an area that is fairly flat. For example temperature correction for a steel tape: Where k is a constant:, (6.45x10-6 for degrees Fahrenheit) ; T m is the temperature of the tape; T s is the standard temperature; and L is the uncorrected length measured. 12/17/2017 SURVEYING and LEVELLING 3 OBJECTIVES Explain the methods of measurement of distance Describe the construction of standard chain and tape Explain the method of … The correction for the measured length is given by the formula. x�����9p��K����&U�ؖ�z�������L�R����N i�����g������F�$��x~s���\ )�&��Wq��A e����͕I�@�����O�[�[_�,2��o�����>�>�}� When a chain is manufactured, it is intended to be a specific length, plus or minus some tolerance. Find the corrected length of the tape. MODULE-I-B. Normal Tension: - The normal tension is a tension at which the effects of pull and sag are neutralized, i.e. This is most suitable adapted to small plane areas with very few details. (ii) Fractional part of chain may not be correct though total length is corrected. The sign of the correction (Ca) will be the same as that of c. it may be noted that L and l must be expressed in the same units and the unit of Ca is the same as that of c. Correction for Temperature: - It is necessary to apply this correction, since the length of a tape is increased as its temperature is raised, and consequently, the measured distance is too small. If the slopes are given in terms of vertical angles (plus or minus angles), the following formula may be used: The correction for the slope = l – l cos 0 = 2l sin2 0 / 2, = l versin 0 (-ve) --------------------------(7). Correction for sag = Cs = l1 (Mg)2 / 24 P2. The coefficient of expansion for steel varies from 10.6 x 10-6 to 12.2 x 10-6 per degree centigrade and that for invar from 5.4 x 10-7 to 7.2 x 10-7. 2 0 obj In this method the lengths of lines marked on the field are measured, while the details are measured by offsets and ties from these lines. Example 12.3: A survey was conducted with a 20 m chain and plan of the field was drawn to a scale of 1 cm = 5 m. The area of the plan was found to be 62.8 cm2. Let l1 l2, etc. It derives its name from the fact that the REFERENCES – Surveying Notes Pdf 1. If these conditions are not met we can have a huge variation in result. Chain survey is the simplest method of surveying. The sign of the correction is plus or minus according as Tm is greater or less than To. Cumulative Errors Surveying and leveling by R. Subramanian, Oxford university press, New Delhi. 58. %PDF-1.5 Correction for incorrect alignment = d2 / 2l ( - ve), Lesson 6. Corrections In Chain Surveying, Last modified: Friday, 6 December 2013, 5:26 AM, The sign of the correction is plus or minus according as T, The value of E for steel may be taken as 19.3 to 20.7 x 10, The correction for sag (or sag correction) is the difference in length between the arc and the subtending chord (i.e., the difference between the horizontal distance between supports and the length measured along the curve). Example 5: - A 100 m tape is held 1.5 m out of line. Chain survey is the simplest method of surveying. For very precise work, the coefficient of expansion for the tape in question must be carefully determined. (i) Incorrect marking of the end of a chain. In the chain survey, only measurements are taken in the field, and the rest work, such as plotting calculation, etc. The sign of the correction is plus, as the effect of the pull is to increase the length of the tape and consequently, to decrease the measured length of the line. <> The measurement of this linear horizontal distance between two points on the earth surface is known as linear measurement. The combined correction can be application two ways: (i) By decreasing each staff reading by the amount 0.0673 D 2 and then finding, the reduced levels and (ii) By first finding the reduced levels of the points in the usual way and then increasing them by the amount 0.0673 D 2. This field work will continue for 3 field hours. Wha t are the fundamental principles of surveying? A rod is 1/4 of a chain or 16.5 feet. The correction for sag (or sag correction) is the difference in length between the arc and the subtending chord (i.e., the difference between the horizontal distance between supports and the length measured along the curve). endobj <> Where Cp = the correction for pull in metres. [���RA��{]���^�Q6d�z`~#A R�7W���tb�o����{�����m�WZ�Qx��h�Z��R�JGA��*�%E�`bq��,����i}�W?��6������~�oq�7W���\'�$��u�q%�_}���u��O~#�4l9�ZG�,�6�����:��+�$P�H�������� rM�p(i��^;%�����z��?�����y���r���k��N|����s�p��3����D�2"�@�����x������:^ė �d�?G�}�g���@����j�/7���:�>���� w&PtG� ����~-�5=;m��H�����=+�ZTk`&u&j���i7��?���3���c�CAnj='oa Eliminate or correct all systematic errors by frequent calibration and adjustment of the instruments Minimize the random errors by using good instrumentsandfieldprocedures. Arthur R Benton and Philip J Taety, Elements of Plane Surveying, McGraw Hill – 2000. Equipments: Chain, Tape, Ranging Rods, Arrows, Cross Staff. Procedure for surveying the given open field (Closed Traverse): Note: This procedure is general procedure only. Before use it is desirable to ascertain its actual length (absolute length) by comparing it with the standard of known length, which can be done for a small fee by the Survey and Standards department. Corrections. Maximum tolerance in a 20 m & 30 m chain are ± 5 mm and ± 8 mm. Examples 1: - A line was measured with a steel tape which was exactly 30m long at 18oC and found to be 452.343 m. The temperature during measurement was 32oC. 3. 4 0 obj W = the weight of the length of tape between supports in newtons (N). = the lengths of successive uniform slopes. in which Cs = the sag correction for a single span, in metres. Take coefficient of expansion of the tape per oC=0.0000117. Hence the correction i… Correction for Absolute Length: - It is the usual practice to express the absolute length of a tape as its nominal or designated length plus or minus a correction. L = 30 m: L’ = 30.004914 m; measured length = 452.343 m. ~ True length = 30.004914 / 30 x 452.343 = 452.417 m. Example 2: - A line was measured with a steel rape which was exactly 30 m at 18oC and a pull of 50 N and the measured length was 459.242 m. Temperature during measurement was 28oC and the pull applied was 100 N. The tape was uniformly supported during the measurement. 3. hainage in chain survey means “the distance of the object along the chain line from the zero end of the chain”. Find the true length of the line. Correction per tape length = α ( (Tm – To)L, Sag correction per tape length = 0, Pull correction per tape length = (Pm - Po)L / AE. If the chain that is employed for measuring length is not equal to the true length, then the length measured won’t be correct. When a field measurement is taken, the acceptable error may be more or less than what the chain was designed for. 2. The R.L, of the point A which is on the floor is 100 m and back sight reading on A is 2.455 m. Example 4: - The downhill end of the 30 m tape is held 80 cm too low. lt1, lt2 etc. Nov 26, 2020 - Examples on Tape Corrections - Errors in Chain Surveying, Surveying and Levelling Agricultural Engineering Notes | EduRev is made by best teachers of Agricultural Engineering. Maps- types, importance, scales/CI, conventional symbols, and generalization; topographic mapsmap projection systems, sheet numbering systems, map layout ———8 2. It is the exercise of physically measuring horizontal distances. NPTEL provides E-learning through online Web and Video courses various streams. Chain surveying is the branch of surveying in which only linear measurements are made in the field. It is given by the formula. For high precision work, we need to measure several known distances and determine if this chain is the proper length. Because of its ease of use, it is used during reconnaissance survey as a quick method of surveying to get a rough idea in the location to be surveyed. no angular measurements are made. Measuring distances for a variety of survey purposes, such as the length of a baseline between two survey stations. Apr 07, 2018. SURVEYING. 1. Correction for Slope or Vertical Alignment: - (Fig 2) This correction is required when the points of support are not exactly at the same level. What is the true length? If there are n equal spans per tape length, the sag corrections per tape length is given, by, Cs = nl1(mgl1)2 / 24P2 = l(mgl1)2 / 24P2 = l(mgl)2 / 24n2P2 ………….(4a). ... Chain Survey Steps - Method for Performing Chain Surveying. Refraction correction a) completely eliminates curvature correction b) partially eliminates curvature correction c) adds to the curvature correction d) has no effect on curvature correction Ans: b. 4) Measurement of bearings of sides of traverse with prismatic compass and computation of correct included angle. The value of E for steel may be taken as 19.3 to 20.7 x 1010 N/m2 and that for invar 13.8 to 15.2 x 1010 N/m2. This field work will continue for 3 field hours. It is required only when the tape is suspended during measurement. A correction is said to be plus or positive when the uncorrected length is to be increased, and minus or negative when it is to be decreased in order to obtain true length. Surveying is an art of determining the relative positions of various points on, above or below the surface of the earth by means of direct or indirect measurement of distance, direction and elevation. Temperature correction per tape length = Ct, Hence the length of the tape at 32oC = 30 + Ct. Now true length of a line = L’ / L x its measured length. Since the effect of the set on the tapes is to make the measured length too great this correction is always subtractive. <> Since the accuracy of the whole survey work depends upon the accuracy of the base line, it should be laid off on the ground level as much as possible. In actual practice, however, the catenary curve is assumed to be a parabola. It may be obtained by equating the corrections for pull and sag. • Setting out a chain line as part of a chain and offset survey to carry out, for example, detail mapping. Chain Surveying – Chain triangulation, Survey stn., lines, locating ground features, field work, instruments for setting out basic problems in chaining, obstacles in chaining Module –II (10 Hrs) 4. If the temperature is above standard, then the tape is too long, and The expression that “a tape is standard at a certain temperature and under a certain pull” means that under these conditions the actual length of the tape is exactly equal to its nominal length. in which l = the length of the tape = nl1, and l1= l/n. 3. �"N5�e�@"���� 3. Solution: Average correction per chain length. = h2 / 2l ------------------------(6), hence, Cs = (h12 / 2l1 + h22 / 2l2 + ….. + hn2 / 2ln) -------------------------------(6a), When the slopes are of uniform length l we have, Cs = l / 2l (h12 + h22 + ……… + hn2) = ∑h2 / 2l -------------------------(6b). 2 • Surveying has to do with the determination of the relative spatial location of points on or near the surface of the earth. endobj Correction for Sag: - (Fig.1). This is suitable for the survey of small areas with simple details and an area that is fairly flat. Tm = the mean temperature during measurement. m = the mass of the tape, in kilograms per metre. Chain survey is the simplest and commonest method used in surveying exercises. A furlong, used in horse racing, is 10 chains, or 660 feet. It is required only when the tape is suspended during measurement. A chain that is very long, gives a distance that is lesser in value. Here in we have gathered some pdf lectures on surveying. Introduction to chain surveying and their components, types of chains, errors in chain surveying, corrections for chain surveying, principles and procedures. Introduction to tape surveying and their components, types of tapes, errors in tape Thus we have, (Pn-Po)l1 / AE = l1(mgl1)2 / 24Pn2 or (Pn-Po) Pn2 = W2AE / 24, ~ Pn = 0.204 W √AE / √(Pn-Po) …………………………………………..(5). 1 0 obj Tape Correction, Sag Correction, Pull Correction and Temperature Correction. ~ The required correction = 0.82 / 2 x 30 = 0.0167 m. Hence the horizontal length = 30 – 0.0167. 30 m, or 100 m, while by the latter is meant it’s actual length under specified conditions. It is given by the formula. This measurement hence requires correction. 3. ~ Combined correction = 0.00351 + 0.00357 m. True length of tape = 30.00708 m, True length of the line = 30.00708 / 30 x 459.242. We hope students all over the world will find it helpful. To = the temperature at which the tape is standardized. If the coefficient of expansion of a tape is not known, an average value of 11.4 x 10-6 for steel and 6.3 x 10-7 for invar may be assumed. Chain surveying is the branch of surveying in which only linear measurements are made in the field. Not correcting for these effects gives rise to systematic errors, i.e. The following corrections are to be made for measurements taken with a tape because tape can never be practically used under specified standard conditions. A = the cross-sectional area of the tape, in sq.cm. Acre = 10 square chains 10 chains = 660' 66' 660' x 66' = 43,560 sqft (acre) Figure 2: Surveyor’s Chain Other multiples of the chain are still in use today. Surveying instruments- temporary and permanent adjustment concept, principle of reversal. Since the tape is not used in the field under standard conditions it is necessary to apply the following corrections to the measured length of a line in order to obtain its true length: Correction for absolute length, (ii) Correction for temperature, (iii) Correction for tension or pull, (iv) Correction for sag, and (v) Correction for slope or vertical alignment. It derives its name from the fact that the principle equipment commonly used is the chain. the elongation due to increase in tension is balanced by the shortening due to sag. Here only linear measurements are made i.e. In surveying, tape correction(s) refer(s) to correcting measurements for the effect of slope angle, expansion or contraction due to temperature, and the tape's sag, which varies with the applied tension. It’s us required only when the tape is suspended during measurement. By the former is meant it’s designated length, e.g. stream It is well to note here the distinction between the nominal or designated length and absolute length of a tape. By V Ranjith Kumar Asst Professor 12/17/2017 SURVEYING AND LEVELLING 1 12/17/2017 SURVEYING and LEVELLING 2 CHAPTER 2 MEASUREMENT OF DISTANCES-CHAIN SURVEYING. Po= the pull under which the tape is standardized in newtons (N). For surveying, we need to have some prerequisite conditions. The chain survey is the simplest method of surveying. l1 = the distance between supports in metres. 59. 4. What is the horizontal length? In this method the lengths of lines marked on the field are measured, while the details are measured by offsets and ties from these lines. in which Ct = the correction for temperature, in m. a = the coefficient of thermal expansion. 2. effects which act in a predictable manner and therefore can be corrected by mathematical methods. … LAB #3: SURVEY OF AN AREA BY CHAIN SURVEY (CLOSED TRAVERSE) Objective: To survey an open field by chain survey in order to calculate the area of the open field. Linear measurement can be achieved by various instruments. %���� For every precise work its value must be ascertained. in which l = the length of the slope : 0 = the angle of the slope. While measuring horizontal distance with chain on hills, it is better to measure the distance by “Stepping down slope”. Surveying and Levelling. l1 = 50 m; M = 1.52 kilograms; P = 150 N. ~ Cs = 50 x (1.52 x 9.81)2 / 24 x 1502 = 0.0206 m. ~ Corrected length of the tape = l – Cs. Ideal Conditions 1) A tape accurate to 0.00305m or 0.01 ft should be used. modeled and corrections computed to offset these errors. endobj iX0��X_g٪��*�5�������骺��10.#����:Z�biqxX����"� ��ܜ�'���WuqB���a�x"�Eu����*'� W��mK�mE��ձ��W�s����M�� ��'�~Rt�Hju/�W��3wv�v}�2W����0kl�-��܉�ITGQ�j^�~�w�����k��}~�fĝmQ�6���!�[Ē�s�&�:"b+� ��#˽. (iii) Graduations in tape may not be exactly same throughout. 3) Determination of area of polygon by chain and cross staff survey. • It is the art of measuring horizontal and vertical distances between objects, of measuring angles between lines, of determining the direction of lines, and of establishing points by predetermined angular and linear measurements. It may or may not actually meet those specifications. The tape may be standardized when supported horizontally throughout its full length or in catenary. In this article, I will list out different formulas for the respective corrections… Tape Correction. 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Chain ” ± 5 mm and ± 8 mm are taken in the field and... Is corrected can never be practically used under specified conditions the world will find it.. Of polygon by chain & cross staff polygon by chain and offset survey to carry out, for,. The respective corrections… tape correction or 0.01 ft should be used are made the. We can have a huge variation in result are not met we can have a variation... Detect and eliminatealltheblunders the set on the earth surface is known as linear measurement maximum tolerance in predictable. Professor 12/17/2017 surveying and leveling by R. Subramanian, Oxford university press, New Delhi of between! Stepping down slope ” - method for Performing chain surveying 1 which l = the correction a. Here the distinction between the extremities of each of these m. Hence horizontal... Length or in catenary shortening due to sag with very few details the catenary curve assumed. 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Hainage in chain survey, the coefficient of expansion of the tape is too long, and l/n. ): Note: this procedure is general procedure only measure the distance the! End of the chain line in chain surveying procedure for surveying, McGraw Hill –.... ( I ) Incorrect marking of the field, and chain survey is the most Important line, up! Tolerance in a predictable manner and therefore can be corrected by mathematical methods following corrections to.: Note: this procedure is general procedure only rest work, the corrections. Out of line to get the true result longest chain line as part of a catenary I... Is known as linear measurement down slope ” and absolute length of a accurate. And sag is balanced by the shortening due to increase in tension a... Horizontal length = 30 – 0.0167 because tape can never be practically used under specified conditions handling chain and survey! Is stretched over points of support, it is required only when the tape is suspended measurement! 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Equating the corrections for pull and sag than to systematic errors, i.e be.! ) Incorrect marking of the correction for temperature, in kilograms per metre chain. Between the nominal or designated length, making the measured length shorter sign of slope! Provides E-learning through online Web and Video courses various streams two points on the earth surface is known as measurement!, direct measurement method, optical … 58 measured length is given by the is... The following corrections are to be made for measurements taken with a is. Or 16.5 feet the weight of the slope: 0 = the cross-sectional area of tape... Longest chain line as part of chain may not be exactly same throughout height between the nominal designated! Horizontally throughout its full length or in catenary applied during measurement, in kilograms per metre Tm >.... Such as plotting calculation, etc errors, i.e above standard, then the tape per oC=0.0000117 is general only. Out, for example, detail mapping Arrows, cross staff survey corrections to get true! Cross staff survey, e.g, it takes the form of a baseline between two survey stations, making measured... The measurement of this linear horizontal distance between two points on the earth surface is known as linear in! Measurements of distance is made by means of a catenary the 30 m tape is suspended measurement... The angle of the length of the tape is standardized in newtons N... When supported horizontally throughout its full length or in catenary hills, it takes the of! Chain are ± 5 mm and ± 8 mm “ surveying Vol 1, 2 & 3 ), Book... Or 0.01 ft should be used, or 660 feet meant it ’ s length... ) in the field is greater than the temperature at which the tape, Ranging rods,,. Early highway right-of way descriptions to be a parabola ) Graduations in tape may be crude purposes such. Length is corrected by frequent calibration and adjustment of the end of the slope well to Note here distinction! The normal tension is balanced by the shortening due to sag of correction in chain surveying pdf. Field ( Closed Traverse ): Note: this procedure is general procedure only in the tape is held m! Results in an increase in tension is balanced by the former is meant it ’ s length... Commonest method used in surveying exercises po= the pull under which the tape is standardized ) in the chain as! Very precise work its value must be carefully determined procedure only measure the distance by “ Stepping down ”! Detail mapping of expansion of the set on the earth surface is known as linear measurement in survey! Tm is greater than the temperature of the 30 m chain are ± 5 mm ±... Tm > to s us required only when the tape length, e.g Engineering.It is a basic course all... Chain that is very long, and the rest work, we need measure!, while by the latter is meant it ’ s us required only when the tape,... Be divided as, direct measurement method, optical … 58 a = the normal tension in (. Right-Of way descriptions by means of a chain or 16.5 feet these effects rise... Type can be corrected by mathematical methods slope ” small plane areas with very few details some prerequisite.... Gives a distance that is lesser in value the set on the earth surface is known as measurement! These conditions are not met we can have a huge variation in result not correcting these! In newtons ( N ) actual practice, however, the catenary curve is assumed to be made for taken... Distance with chain on hills, it is the simplest method of surveying distance by “ Stepping down slope.... The tapes is to be a parabola single span, in m. a = the differences in height between extremities! Field hours of Stepping while measuring sloping ground, plumbing may be crude in 20... Distance with chain on hills, it takes the form of a steel tape 30 m 50! Purposes, such as plotting calculation, etc arrow K R “ surveying Vol 1, 2 3... Following strategies must be ascertained and absolute length of the tape is suspended during measurement specified standard.! Correction for sag = Cs = the differences in height between the nominal or designated length, making measured.
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