# Surveying a Level Loop - CCSMS Engineering

Surveying a Level Loop Level Loop (or Closed Circuit) Instrument location (TYP) FS 4.26 ft BS ft 3 .1 7 = 1 Elev. 100.00 ft Turning Point (TYP) Closed Circuit or Level Loop AUTO LEVEL READINGS STADIA PT (+) BS

BM 7.13 TP-1 HI (-) FS ELEV 107.13 X 100.00 4.26 102.87 TOP/BOT STADIA DIST /Angle

Level Loop (or Closed Circuit) = S B Elev. 100.00 ft f 5 1.7 FS = 2.99 ft t 2 Turning Point Elev. 102.87 Closed Circuit or Level Loop AUTO LEVEL READINGS STADIA PT (+) BS

BM 7.13 107.13 X TP-1 1.75 104.62 4.26 102.87 2.99 101.63 TBM HI (-) FS ELEV 100.00

TOP/BOT STADIA DIST /Angle Level Loop (or Closed Circuit) BS = 5.62 ft Elev. 101.63 ft 3 ft 5 FS 8 ft 9 . =7 BS = 0.94 ft

4 =6 .01 4 3.3 BS = 9 .12 ft FS = FS ft Elev. 100.00 ft Closed Circuit or Level Loop AUTO LEVEL READINGS STADIA PT (+) BS BM

7.13 107.13 X TP-1 1.75 104.62 4.26 102.87 TBM 5.62 107.25 2.99 101.63 TP-2 0.94

102.18 6.01 101.24 TP-3 9.12 103.32 7.98 94.20 3.34 99.98 POR HI (-) FS ELEV 100.00 TOP/BOT

STADIA DIST /Angle Closure Error The difference between a measured or calculated elevation and the true or established elevation. Closure Error = Final Elev. Initial Elev. Closed Circuit or Level Loop AUTO LEVEL READINGS STADIA PT (+) BS BM 7.13 107.13 X TP-1

1.75 104.62 4.26 102.87 TBM 5.62 107.25 2.99 101.63 TP-2 0.94 102.18 6.01 101.24 TP-3

9.12 103.32 7.98 94.20 POR HI (-) FS ELEV 100.00 3.34 99.98 - 100.00 CLOSURE ERROR = - 0.02 ft TOP/BOT STADIA DIST /Angle

Allowable Error The allowable error depends on the type and purpose of the surveying. In this class, we will use Closed Circuit or Level Loop AUTO LEVEL READINGS STADIA PT (+) BS HI (-) FS BM 7.13 107.13 X TP-1 1.75

104.62 4.26 TBM 5.62 107.25 2.99 TP-2 0.94 102.18 6.01 TP-3 9.12 103.32 7.98 POR

3.34 ELEV TOP/BOT STADIA 100.00 BS 8.63 / 5.63 102.87 FS 5.69 / 2.83 BS 3.15 / 0.25 101.63 FS 4.44 / 1.54 BS 6.67 /4.57 101.24 FS 7.08 / 4.94 BS 1.84 / 0.04 94.20 FS 8.94 / 7.02 BS 10.42 / 7.82 DIST /Angle 300 ft 286 ft 290 ft 290 ft 210 ft 214 ft 180 ft 192 ft 260 ft 248 ft 99.98 FS 4.58 / 2.10

- 100.00 TOTAL = 2470 CLOSURE ERROR = - 0.02 ft ft Level Loop (or Closed Circuit) Instrument location (TYP) 290 0f 0 3 290 ft 210 ft 286 ft ft t 3 8 24 ft

5 ft 192 180 ft 4 21 4 ft Elev. 100.00 ft 260 ft Elev. 101.63 ft Allowable Error Survey data is acceptable Reducing Errors Check that bubble is centered for EVERY rod reading. Keep the rod plumb during each reading. Establish equal BS and FS reading distances. Equal reading distances will cancel out any error

caused by the line of sight not being parallel with the axis of the bubble tube. This is not always possible due to terrain. Common Errors Faulty rod reading (verify reading) Rod not fully extended (high reading) Tripod movement during reading Confusion between recording BS and FS entries in the field book Can You Top That? Courtesy NOAA Photo Library http://www.photolib.noaa.gov/htmls/theb1809.htm According to NOAA, this survey party made 329 setups in 7 hours and 55 minutes working in an area of extreme grades in the Western United States in 1934. Image Sources National Oceanographic and Atmospheric Administration Photo Library http://www.photolib.noaa.gov/cgs/marks1.html

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