Part 2 DISTANCE MEASUREMENT

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Section 2 DISTANCE MEASUREMENT. Perused Chapter 2 Kavanagh2.1-2.6 Read to supplement class lecture2.7, 2.18Read to supplement field exercise2.8-2.17Understand taping adjustments, wellsprings of blunder, arbitrary and methodical mistakes, and efficient blunder revision. 2.2 Taping (or

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Section 2 DISTANCE MEASUREMENT 3/17/03

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CHAPTER 2 DISTANCE MEASUREMENT Read Chapter 2 Kavanagh 2.1-2.6 Read to supplement class address 2.7 , 2.18 Read to supplement handle practice 2.8-2.17 Understand taping adjustments, wellsprings of mistake, arbitrary and systematic blunders, and methodical mistake revision

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2.2 Taping (or "Anchoring") In 1800's, U.S. Government Land Office studies which divided the land for homesteading utilized Gunter's 66' chain. This century, the steel strip tape is generally normal. Be that as it may, "taping" and "anchoring" terms still utilized. Two sorts of chains: 66-ft Gunter's chain & 100-ft designer's chain. If not generally indicated (especially if taking a gander at nineteenth century maps) 66-ft chain is implied.

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2.2 Taping, cont. Steel tapes: Invar tapes (not normal): Cloth and fiberglass tapes:

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2.2 Taping, cont. Why taping is utilized for <100' separations: Nikon A-10 EDM exactness: 5 mm consistent mistake ± 3 ppm blunder for instrument = ± 0.02' Add setup mistake 0.01' or 0.02' Total EDM estimation mistake possibly 0.03' > 1/10,000 mistake in great taping = 0.01', or 1/5000 mistake standard = 0.02' for 100' dist.

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2.3 Taping Methodology Reading a steel tape Add tape (most normal): Cut tape (more inclined to mistake):

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2.3 Taping Methodology, cont. Great practice is to gauge all separations both forward and in reverse. A taping group ought to have the accompanying hardware 1) 1-100' steel tape 2) 3-territory posts 3) 1-set of 11 binding pins (additionally called "taping pins") 4) 1-50' woven or fabric or fiberglass tape 5) 2-plumb weaves 6) 1-hand level 7) 1-tape brace

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2.3 Taping Methodology, cont. Taping over Level Ground (Distance > 100 ft.) 1) If the separation to be measured is level, you may lay the tape on the ground. 2) The head tapeman takes the 0' end at the tape and strolls in the bearing to be taped. 3) When the back tapeman gets to 100' on the tape he calls "tape" or "chain" to stop the head tapeman. 4) The back tapeman then adjusts the head tapeman using a range shaft set behind the end point. 5) Once found, the back tapeman places the 100' check over the beginning stage and the head tapeman pulls the tape tight to 10-15 lb strain (to the predetermined standard pressure). 6) If on soil, a taping pin is embedded z to the tape at a vertical edge of 45E± If on asphalt, stamp zero point with chalk, colored pencil, or copyist it. Leave a taping pin alongside the point for the back chainman to get.

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2.3 Taping Methodology, cont. Taping over Level Ground (Distance > 100 ft.) 7) Once an estimation have been made, the back tapeman gets the taping pin. By counting taping pins, the back tapeman knows what number of 100' lengths have been measured. 8) When the finish of the separation to be measured is achieved, the head tapeman stops at the point. The back tapeman pulls the tape to an entire foot stamp that will bring the subgraduations at the zero end of the tape over the point denoting the finish of the line. 9) The take tapeman then peruses off the perusing on the graduated bit of the tape to the nearest hundredth foot.

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2.3 Taping Methodology, cont. Taping over Sloping Ground Two taping techniques: Hold the tape level. Tape along the incline, process the slant, adjust for the slant.

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2.3 Taping Methodology, cont. 1) Slope Taping: Horizontal Taping Method Same methodology as level ground technique with taking after included documentations: One or both tapemen may need to hold the tape off the ground. Utilize a plumb bob to position the tape over the stamp. Downhill tapeman may need to utilize a hand level to ensure both finishes are at a similar tallness. In the event that relative precision superior to 1/2500 - 1/3000 is coveted, visual perception not sufficient. On the off chance that S < 5'/100' (<5% review) you can quantify a whole 100' flat separation (i.e., on the off chance that you can hold the tape at shoulder level or lower).

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2.3 Taping Methodology, cont. 2) Slope Taping: Taping Along the Slope Lay tape on the incline Suitable for smooth and steady slant; can be more exact than level taping since it is hard to hang a plumb sway from the tape precisely. Utilize travel or theodolite to decide incline (ft/ft) or review (%).

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2.4 Applying Corrections to Tape Measurements Types of Systematic Errors Tape Characteristics 1) Incorrect tape length (institutionalization mistake) 2) Temperature variety (from standard temperature) 3) Sag 4) Non-standard strain Operational blunder 5) Tape not flat (when accepted level) or blunder in evaluating slant 6) Incorrect arrangement (tape is disconnected) 7) Tape not straight (bowed around trees or shrubs) Applying rectifications: measured length + Correction = real length

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2.4 Applying Corrections, cont. 1) Incorrect Tape Length or Standardization Error During assembling, the tape was graduated under standard temperature (say 68E), strain (say 10 lb), and technique for support (completely bolstered). The contrast between the genuine tape length (under indicated states of temperature, pressure, and strategy for support) contrasted with a standard length and the ostensible tape length = "supreme blunder" of the tape. Total rectification Ca = genuine length - ostensible length Example: A separation was measured and observed to be 876.24 ft. The tape was later observed to be 100.04 feet long. What is the right separation? Supreme remedy Ca happens 8.76 circumstances = 8.76 x 0.04 ft = 876.24 ft x 0.04 ft for each 100' measured = 0.35 ft measured length + Correction = genuine length 876.24 ft + 0.35 ft = 876.59 ft Summary: If the tape is too long we didn't utilize it enough circumstances so the real separation is longer .

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2.4 Applying Corrections, cont. 2) Temperature Variation Coefficient of warm development of steel, k = 6.45 x 10 - 6/º F (Note: Invar coef. of warm development is around 1/30th that of steel) Difference of 15 º F ± 0.01 ft in a 100-ft tape The redress to be added to the deliberate separation to get the genuine separation: C t = Lk(T-T s ) where C t = adjustment to be connected (ft or m) L = length of tape utilized k = coefficient of warm extension T = temperature of tape amid estimation T s = temperature at which tape was institutionalized Temperature of tape completely bolstered on ground may >> air temp. Utilize tape thermometer joined to the tape.

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3) Sag Correction for hang required when tape has been institutionalized with a completely upheld length. Tape takes type of catenary, and flat length is abbreviated: C s = - n w 2 l 3 (ft or m) 24P 2 Where n = number of unsupported lengths w = weight/foot of tape l = unsupported length P = strain connected (lb or kg) Due to hang, the watched (measured) separation is constantly more noteworthy than the genuine separation. Adjustment length to be added to measured separation to acquire genuine esteem is dependably a negative esteem. Measured Distance + C s = True Distance One approach to limit the droop amendment is to limit the length of tape in the sag. OR increment the tape strain adequately to make up for the impact of list.

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4) Non-standard strain If you pull a tape in pressure it will extend. The National Bureau of Standards institutionalizes the tapes under 2 conditions: 1) 12 lbf pull, completely bolstered (Note: FE2's tape was institutionalized at 15 lbf pull) 2) 20 lbf pull, completely unsupported Correction for draw or pressure is: C p = (P-P s ) L AE where P = strain connected (lb or kg) P s = standard strain L = length A = cross-sectional zone of tape E = modulus of flexibility of steel = 2.8 x 10 7 to 3.0 x 10 7 psi

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Normal strain = the strain connected to a tape with the end goal that the extending because of pressure equivalents the shortening because of hang. For a full tape upheld at two closures: C s + C P = 0 C s = - W 2 L - W 2 L + (P n - P s ) L = 0 24 P n 2 AE P n = 0.204 W (AE) 0.5 (P n – P s ) 0.5 Solve the condition iteratively utilizing experimentation. On the other hand utilize a diagram provided by the producer. For most tapes P n in the scope of 20 lb. will do.

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5) Tape not flat When tape is expected even but rather is really disposed: For 100' tape, the limit for 0.01' roundoff mistake: H = L cos a 99.995' = 100 cos an a = 0 o 34' 23" or 99.995 2 = 100 2 - d 2 d = 1.00 ft Use a hand level to limit this blunder.

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Departures from typical delivering 0.01-ft blunder per 100' tape length

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Example: Combined Taping Corrections A separation was measured as 365.20 ft on a 8% review. No field adjustments were made, and the incline was viewed as level. The taping was finished with the tape held off the ground along its entire length. The temperature at the time was 18E F. What is the right even separation if the tape is 100.03 ft long under standard conditions? Arrangement: Measured separate = 365.20' Corrections per tape length: Sag

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Temperature Incorrect length Slope

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Total rectification: Corrected level separation =

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2.1 Other Methods of Measuring Distances Pacing Odometer Car odometer exactness = 0.1 mile Measuring wheel with counter joined Stadia tacheometry = methodology that uses two supplementary even hairs ("stadia hairs") put at equivalent separations above and underneath the focal flat hair in an instrument's telescope

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2.2 Methods, cont. Subtense bar (not common) EDMs (EDMIs) Electronic Distance Measurement instruments Either a unit mounted on main a theodolite, or an implicit unit If it can't settled H, V, S consequently, it is usually named "EDM theodolite" Uses infrared l

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