british columbia carpenter apprenticeship program · the transit level (courtesy of cansel ... the...

British Columbia Carpenter Apprenticeship Program

Level 2 Line D

Use Leveling Instruments

7960003551

Competency D-1

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Copyright © 2012 Industry Training AuthorityThis publication may not be reproduced in any form without permission by the Industry Training Authority.Contact Director, Crown Publications, Queen’s Printer at 250 356-6876.

SAFETY ADVISORYPlease note that it is always the responsibility of any person using these materials to inform him/herself about the Occupational Health and Safety Regulation pertaining to his/her work. The references to WorkSafeBC safety regulations contained within these materials do not / may not reflect the most recent Occupational Health and Safety Regulation (the current Standards and Regulation in BC can be obtained on the following website: http://www.worksafebc.com).

BC CARPENTER APPRENTICESHIP PROGRAM—LEVEL 2 1

Competency D-1Use Leveling Instruments

ContentsObjectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Learning Task 1: Review Types of Optical Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Learning Task 1: Self-Test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Learning Task 2: Review Care of Optical Levels and Other Layout Instruments . . . . . . . . . . . . . . . . . . . . . 16


Learning Task 3: Reading a Levelling Rod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Learning Task 3: Self-Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Learning Task 4: Describe Setting up, Leveling and Testing an Optical Level . . . . . . . . . . . . . . . . . . . . . . . 27


Learning Task 5: Review Setting and Measuring Elevations Using Optical Levels . . . . . . . . . . . . . . . . . . . . 32


Learning Task 6: Identify Parts and Describe Use of Laser and Electronic Levels . . . . . . . . . . . . . . . . . . . . 40


2 BC CARPENTER APPRENTICESHIP PROGRAM—LEVEL 2

Competency D-1Use Leveling Instruments

The construction of buildings requires the carpenters to set and measure elevations. The elevations of foundation walls, floor levels and exterior grades are given on the drawings, the building must be built to the specified elevations.

The carpenter must be able to set up and use an instrument to establish and check elevations. To be able to do accurate leveling work, the carpenter must know how to determine if the instrument is operating accurately.

ObjectivesWhen you have completed the Learning Tasks in this Competency, you will be able to:

• describe types of optical levels

• identify parts of a level and state the function of each part

• identify parts and scales of leveling rods, chains and tapes

• describe rules for care of optical and laser levels

• identify common errors that contribute to incorrect measurements

• describe methods of setting up and operating levels

• describe methods of recording elevations in a field book

Competencies Written: “Use Optical Levels” You will be tested on your knowledge of the construction and use of levels.

Practical: You will be required to set up and test optical levels for accuracy, and read leveling rods. You will perform various leveling operations and record your readings, using conventional field book practices.


Notes

COMPETENCy D-1 LEArnInG TASk 1

Learning Task 1Review Types of Optical Levels

The optical level is a high-powered telescope equipped with crosshairs (somewhat like a telescopic sight for a rifle). It is centrally mounted on a bearing so that it can rotate only horizontally. A very sensitive spirit bubble is mounted on the telescope, and when this bubble is centered, the instrument is level to the line of sight.

When mounted on a tripod, the optical level is adjusted with foot screws to center the spirit bubble. As the optical level is rotated through a horizontal circle, the bubble may or may not have to be reset to centre depending on the type of optical level being used.

The term optic is used since the eye is used to sight through the level in order to take a reading. Laser levels are not sighted through, and are not a type of optical level.

The Automatic Level Figure 1 shows an automatic level. Another name for this instrument is the self-leveling level.

Figure 1. The automatic level (Courtesy of Cansel Survey Equipment)

Automatic levels have either three leveling screws, or are the quickset type. They are equipped with a fisheye bubble, and great care must be taken in centering this bubble. When the bubble is in the centre of the fisheye, no further adjustments are required. The instrument will automatically adjust the line of sight as the operator moves it from reading to reading.

Notes


LEArnInG TASk 1 COMPETENCy D-1

Automatic Leveling System Modern leveling instruments are built with an automatic leveling system. A compensator (hanging prism) automatically levels the line of sight. The prism is suspended by very fine wires and will swing to a plumb position automatically whenever the instrument is turned to a new position.

Some automatic levels have a little button to push to ensure that the prism is hanging freely. If there is no button, a light tap on the side of the instrument will accomplish the same thing. The image you see should sway slightly, then stabilize. Figure 2 shows a schematic diagram of how the hanging prism levels the line of sight.

HANGING PRISM

LINE OF SIGHT

Figure 2. Prism used in automatic levels

If an automatic level is shaken gently there is a faint metallic rattling sound caused by the suspension system of the prism.

The Transit Level Levels of any type are designed for horizontal rotation only. Where some levels can, to a low degree of accuracy, measure horizontal angles, this work is done mainly with transits and theodolites which are capable of both horizontal and vertical angular measurement (vertical ones up to ± 45° from horizontal).

The transit level, shown in Figure 3, is designed so that it can be used to perform both leveling and angular measurement operations, and many contractors consider its degree of accuracy adequate.

Figure 3. The transit level (Courtesy of Cansel Survey Equipment)


Notes


Parts of a Level Major working parts of various levels are identified in Figure 4. The functions of these parts and some others are described on the following pages.

1. Focusing knob

2. Azimuth fine adjustment screw

3. Metal mirror (folded)

4. Metal mirror (open)

5. Circular level

6. Tubular level

7. Telescope eyepiece

8. Foot screw (screw thread

dust protected and encased)

1

17

7

3

4

45

5

6

2

2

8

8

Figure 4. Levels with labelled parts

Telescope Eyepiece The eye is positioned at the telescope eyepiece when a reading is being taken. The knurled adjustment ring found here is for focusing the crosshairs.

Notes



Crosshairs The crosshairs are vertical and horizontal lines that are used to line up with a surveyor’s rod in order to take a reading. The vertical hair can be used to line up an object for plumb. The centre horizontal hair is used for making elevation measurements. There are two additional shorter horizontal crosshairs above and below the central cross hair. These two lines are called stadia lines and they are used to measure distance.

Figure 5. Crosshairs

The crosshairs are etched on a piece of glass called a reticule. If the instrument is dropped, the reticule may be jarred out of position making the line of site out of parallel with the base of the instrument.

Doing a peg test checks the position of the reticule. If crosshairs are found by the peg test to be out of alignment, they can be adjusted back into position using the small adjustment screws located just forward of the eyepiece. This procedure is described in Competency D-1, Learning Task 4.

Telescopic Barrel The telescopic barrel contains the lenses and focusing ratchet mechanism. The lens opposite the eyepiece is called the objective lens.

Focusing Screw The focusing screw brings the object seen through the eyepiece into sharp focus by moving the lenses inside the barrel.

Leveling Bubble The leveling bubble can be located above or below the barrel, as on a Dumpy level, or alongside it, as on an engineer’s level. The length of the bubble expands and contracts with changes in temperature.

Figure 6. Tubular level


Notes


Fish Eye Bubble The fish eye or circular bubble is used to roughly level surveying instruments.

Automatic levels use fish eye bubbles to get the instrument level enough that the automatic leveling device will adjust the line of sight to level.

Horizontal Tangent Screw The horizontal tangent screw is used to rotate and to accurately aim the telescope horizontally. Usually it is located just below the objective lens.

Tripod Head Plate The instrument is attached to the head plate of the tripod. The instrument is attached with a screw, the thread type of the screw must match the thread of the instrument.

Tripod The tripod is a three-legged stand with adjustable legs, used to support the instrument. The legs must be firmly set into the ground to keep the instrument in the same position during the surveying work.

Leg Thumbscrew or ClampLeg thumbscrews or clamps are used to adjust the length of the individual legs of the tripod. Adjust the legs to level the tripod head before attaching the instrument to the tripod head.

Sunshade The sunshade is a short tube attached to the objective lens end of the barrel to eliminate sun glare.

Figure 7. Fish eye bubble

Notes



The Level Rod There are many types of level rods. They can be made of wood, fiberglass or aluminum alloy. They can be telescopic or can come in sections that are bolted together or that fit one segment into the end of another. There are several different methods of displaying the scales. The type most suited to construction seems to be the segmented type with a reflective face. They are easily dismantled for use in confined spaces and a light source can be shone on the scales for easy reading in poor light conditions. Figure 8 contains illustrations of different rods.

Figure 8. Level rods (Courtesy of Cansel Survey Equipment)

rod Scales Scales in the metric system are generally shown in 10 mm (1 cm) divisions. It has been the practice in the metric system to visually break down the 10 mm divisions. With a bit of practice you will have no difficulty in making rough estimates to the closest millimetre (± 1 mm), which is considered an acceptable tolerance. For more accurate readings, a target that has the 1 cm scale divided up into millimetres can be fitted on the rod, or a portion of a metric tape measure can be held with the rod. Figure 8 shows some scales and readings as they would be taken at the horizontal cross hair of the level. The reading shown in this diagram is 0.845 m.


Notes


Figure 9. Metric rod scale readings Figure 10. Imperial rod scale readings

The Imperial system of feet is used on both the architectural and the engineer’s rod. The architectural rod is broken into feet, inches and fractions of an inch. The engineer’s rod is divided into feet and hundredths of a foot (Figure 12). You can quickly tell if it is an architectural or engineer’s rod by looking for the 11” marking. The engineer’s rod does not show the 11” mark, while the architectural rod does.

Architectural rod readings (Figure 11) are divided into �⁄�” increments. The marks with the point at the end are at the 0” mark and the 4⁄�” or ½” mark.

Engineer’s rod readings (Figure 12) are divided into 0.01’ (�⁄100’) increments. The marks with the point at the end are at the 0.1’ mark and the 0.05’ mark.

Care should be taken when reading the engineer’s rod: 0.6’ = 7 ¼”, NOT 6”.

Figure 11. Architectural rod Figure 12. Engineer’s rod

Notes



Stadia Lines Stadia lines (or hairs) are used to find the distance from the instrument to the rod (Figure 13).

The accuracy of the stadia line distance measurement is dependant upon how accurate the rod reading is. For example, if the stadia line reading was accurate to one millimetre, then the resulting distance would be accurate to plus or minus 100 millimetres. Stadia line distance measurements are NOT accurate enough for laying out a building on a lot.

To find the distance:

1. take the reading at the top stadia line and at the bottom stadia line

2. subtract the smaller reading from the larger reading

3. multiply the result of the subtraction by 100

The resulting distance is the distance from the instrument to the rod. The system will work with both imperial or metric rods.

Using the Level Rod In order that accurate information is obtained, the level rod must be held plumb whenever a reading is taken. The instrument person can see through the telescope whether the rod is being held plumb in one direction only. To obtain plumb in the other direction, the instrument operator must give a signal to the rod person to move the rod through a small arc forward and backward, so that the lowest reading can be taken. The illustration in Figure 14 should help in understanding this.

Figure 14. Moving the rod through a small arc, forward and backward

Figure 13. Crosshairs and stadia lines


Notes


The device shown in Figure 15 contains a fisheye bubble, and can be used to plumb the rod.

Figure 15. Fisheye attached to rod Figure 16. Target for attaching to rod (Both Courtesy of Cansel Survey Equipment)

The target in Figure 16 is used as an aid in making readings when the rod is at a great distance from the instrument. The target is moved up and down on the rod by the rod-person as directed by the instrument-person. The rod reading is taken by the rod-person and relayed to the instrument-person.

Chains and Tape Reels These are sometimes called surveyor’s chains or survey chain (Figure 17). Originally a chain meant 4 rods or 66 feet, but since we have converted to metric, the term has come to mean the type of measuring tape.

Figure 17. Poly survey chain (Courtesy of Cansel Survey Equipment)

Notes



The types shown in Figure 18 are referred to as tape reels.

Figure 18. Tape reels (Courtesy of Cansel Survey Equipment)

Tapes Any measuring tape can be used, but because the distances on a construction site can be quite large, it is advantageous to use one that is 15 m or 30 m long.

reading Tapes and Chains Tapes and chains use either metric, architectural or engineer’s scales, just as the rods do. You should be using the same scale on both the rod and the tape.

The tape sags when measuring long distances. You must make a correction if it is critical to have very precise measurements. For general construction work, the amount of sag is not a factor that must be considered, however the tape should be pulled as tightly as possible without breaking the tape.

Also if the weather is very cold or very hot, a correction factor must be used to allow for contraction or expansion.


Notes


Hand Signals Hand signals should be used for communication between the instrument person and rod person. These are necessary so that the work can be done efficiently, without yelling or shouting to each other. Sometimes the distance between the instrument person and the rod person is too great or too noisy for verbal communication.

The following are hand signals that should be used:

OK or all right.

Rod, target or pencil up Rod, target or pencil down Move right.

Finished or mark it Plumb the rod Can’t see the rod

Move left Come closer Further away

Now complete Learning Task 1 Self-Test.



Learning Task 1 Self-Test

1. What is turned to focus the crosshairs?

a. telescopic barrel

b. focusing knob

c. eyepiece knurled adjustment ring

d. reticule

2. A fish eye bubble is also known as a:

a. tubular level

b. leveler

c. dumpy level

d. circular level

3. What is the smallest scale division on the level rod shown in Figure 1?

a. centimetres

b. millimetres

c. decimetres

d. hundredths of a foot

4. Reflective facing on the rod helps to:

a. cut down the glare

b. bring the numbers into sharper focus

c. see the scales better in poor light

d. make the rod waterproof

Figure 1.



In questions 5 to 9, refer to the illustrations in Figure 2. Match the correct hand signal to its description, and place the appropriate letter in the blank provided below.

Figure 2.

5. Rod up ___

6. OK ___

7. Plumb the rod ___

8. Can’t see the rod ___

9. Mark it ___

Notes



Learning Task 2Review Care of Optical Levels and Other Layout Instruments

Survey instruments are constructed to give many years of service in adverse weather conditions but if proper care is not taken in handling them, damage may result.

Instrument Use• During transportation, always store the instrument properly in its case. If there

is any chance that it will be subjected to jarring, give it further protection by enclosing it in a cushioned container.

• When first selecting an instrument, open the lid and carefully look to see how it is secured in its container. You must return it to its container in the correct way after each time you use it. When it is not in use, you must always return the instrument to its container for storage.

• When protective lens caps are not in use, leave them in the instrument container.

• Before the instrument is mounted on the tripod, make sure that the tripod is firmly set up and that all its leg adjusting screws and tripod head screws are properly tightened. The mounting head should be as level to the horizon as you can get it by adjusting the legs.

• If the legs must be on any surface, such as smooth concrete, where the points of the tripod legs are not able to dig in, place the tripod in a triangular frame to prevent slipping, as shown in Figure 1.

• While transporting the instrument from the case to the tripod, always grasp the instrument by its base, where it should be held to avoid any damage to any of its parts.


Notes


Figure 1. Triangular frame for the tripod

• Thread the instrument onto the tripod securely but do not over-tighten. This prevents stripping the threads or putting undue stress on any part of the instrument. If the instrument is not properly fastened to the tripod, and as a result it falls to the ground, it may not be repairable.

• Never force the instrument while turning it horizontally or while making any adjustments. This could result in damage. All adjustable features of any level are designed to be just tight—but never over tightened or forced.

• When the lenses become dusty or, as happens occasionally, a spot of mud lands on a lens, try to wash it off with water. When doing this, do not rub the lens with anything, as this can scratch the lens. The best way to clean lenses is to let them dry completely, then use a camel’s hair brush in a circular motion starting at the center of the lens and working out. Remember to use the brush lightly and blow out any particles of dirt as you proceed.

• Levels are built to be used in rain and snow, but should not be left out needlessly. When you are finished, bring them inside and lightly dry them off (damp dry them), except for the lenses. Lenses should always be left to dry on their own. Secure them in their container, but leave it open so that the machine will completely dry. If you close the container, the moisture will remain inside to corrode both the instrument and the case (if it is made of metal).

Notes



• Avoid sudden extremes in temperature. If the instrument is kept in storage at room temperature then taken directly outside into cold or damp conditions, there is a good chance that the inner lenses will become fogged. Fogging will remain until temperatures inside and outside the instrument equalize, and the moisture trapped within naturally disperses. To avoid moisture build up, survey instruments should be stored at the same temperature at which they are going to be used.

• Extreme heat can expand the air bubble in the level vials, making them very difficult to level. To avoid this, put up an umbrella or some sort of sunshade.

• Avoid using the instrument where there is a lot of vibration, such as from soil compactors, pile drivers, etc. This could put the level out of alignment, thus requiring repairs.

• The way in which an instrument is carried when mounted on its tripod is important (see Figure 2). Leave the horizontal clamp loose so that the instrument can swing if it should accidentally hit anything. If there aren’t overhead obstacles, carry it over one shoulder with the tripod legs facing forward. This will help to avoid hitting the instrument if you should happen to trip. If there are overhead obstacles such as formwork shoring, carry the tripod under your arm with the instrument facing forward. If the route you must take is full of obstacles, and you must climb over walls or up and down ladders, it is always recommended that the instrument be transported in its container.

Figure 2. Carrying the instrument


Notes


• Never jar the instrument by banging it down when you are about to set it up, or at any other time. At all times, deal with the tool as if it were a crate of eggs.

• Never leave the instrument unattended. There are many ways an unattended instrument can be damaged on a busy construction site, such as being hit by a passing concrete truck or a swinging load on a crane. Some contractors paint the legs of the tripod in bright colors and attach streamers of bright surveyor’s tape as a precaution against accidents. Also, the instruments could be stolen if left unattended in a built-up area such as a busy downtown street.

• Check all connections for the various parts of the tripod. Looseness at any of the several connecting points could make it unstable and result in incorrect readings. The wood screw connections of wooden tripods that are subjected to wetting and drying tend to loosen.




Learning Task 2 Self-Test1. While an instrument is being transported from one job site to another it should be:

a. left on the floor of the vehicle without a case

b. properly stored in its case

c. left for the job superintendent to look after

d. moved with just its protective lens caps

2. When an instrument is returned to its case:

a. it can go in any way

b. the case should be left open always

c. the lens caps need not be replaced

d. it must be put back just as it was when it came out

3. Tripods can be set up on any surface without any special precautions.

a. true

b. false

4. An optical level should be picked up by the:

a. telescope

b. focus knob

c. base

d. eye piece

5. When securing an instrument to its tripod:

a. no special precautions are necessary

b. the attaching screw should be done up as tightly as possible

c. distractions are not important

d. the attaching screw should be firm, but not over-tight

6. If lenses become splattered with mud:

a. they can be wiped off with a cloth

b. try to wash mud off with a small amount of water

c. cleaning should be done immediately

d. wet with water and dab the mud off with a camel hair brush



7. When you have finished using a level in the rain:

a. put it back in its case as it is

b. wipe the whole instrument until it is completely dry

c. damp-dry everything except the lenses and close it up in its case

d. damp-dry everything except the lenses and leave the case open until it is completely dry

8. Levels may be used in rainy and snowy conditions.

a. true

b. false

9. Sudden extremes in temperature:

a. have no effect on optical levels

b. could result in fogging up the horizontal swing mechanism

c. will only result in making the instrument too hot or cold to the touch

d. could cause the interior lenses to fog up

10. Allowing the instrument to become hot could result in making the instrument difficult to level.

a. true

b. false

11. When carrying the instrument short distances around the work site,

a. hold it in any manner that is safe and convenient

b. hold it out in front of you under your arm

c. place the instrument on your shoulder with the tripod legs pointing out in front

d. any of the above depending on site conditions

12. Vibration has a bad effect on optical levels.

a. true

b. false

13. Levels are easily misaligned and should be treated like a crate of eggs.

a. true

b. false

Notes



Learning Task 3 Reading a Levelling Rod

The following is an example of reading these types of levelling rods.

Exercise 1a Take the readings of the rods shown in Figure 1.

The large black divisions are 10 mm divisions. To read the rods to the nearest millimetre, the actual millimetre will have to be estimated. For example in rod Reading 3, the reading could be either 2.917 or 2.918 m. If reading these rods to the nearest millimetre from a distance, the resulting readings should be thought to be accurate to plus or minus 2 millimetres.

Figure 1. Rod readings


Notes


Exercise 1b Read the Imperial rods shown in Figure 2. In reading 2, the large “8” indicates the “8 foot” mark. In Reading 1, the small “10” indicates that the reading is in between 10 and 11 feet.

Looking closely at Reading 2, notice that there are eight divisions between the large “8” marker and the smaller “1” marker. This indicates that these are rods that are in feet and inches and that the smallest divisions are �⁄�” of an inch. If the cross hair falls between the smallest divisions, as in Reading 4, choose the mark closest to the cross hair. Reading 4 is 11’ 7 �⁄�”.

7811

READING 4

READING 1

READING 5

READING 2

READING 6

READING 3

5

104

32

9

18

X

69

445

Figure 2. Imperial rod readings in feet and inches

Exercise 1c Determine the readings of the rods shown in Figure 3.

Looking at Readings 1 and 5 you will see that there is a “9” just before the foot marker, this indicates that the rods are in feet and decimals of a foot. These rods are the most common imperial rods, and are used by engineers and surveyors. Read these rods to the nearest 1000th of a foot (0.001). The third decimal place will have to be estimated. Reading 5 is 2.974 feet but it could also be estimated at 2.973 or 2.975.

Notes



11

54

READING 4

READING 1

READING 5

READING 2

READING 6

READING 3

X98

9432

7765

2432

39

1

Figure 3. Imperial rod readings in feet and decimals of a foot

Identify Common Errors That Contribute to Incorrect Measurements There are many errors that can be made while using an optical level. The following is a list of things that can go wrong, resulting in incorrect measurements:

1. The instrument must be level each time a sighting is taken to avoid incorrect rod readings. There are three reasons the instrument could be out of level:

a. The instrument was not level to begin with.

b. The instrument was accidentally moved between sightings.

c. The instrument was set up on an unstable surface, such as soft ground, frozen ground or a wooden floor, and some settlement or movement occurred.

2. The rod is often incorrectly read. Whenever you take a sighting, say the reading aloud, and then repeat the reading. There is no special way to avoid this sort of error, but taking the reading twice will help.

3. If the instrument is set up too far away from the rod, the figures on the rod are too small to see properly. The instrument should be set up about halfway between a bench mark and the location where the reading is to be taken. Equal length backsights and foresights will cancel errors caused by the cross hairs not being in perfect adjustment.


Notes


4. The instrument is improperly focused. Make sure the crosshairs are in sharp focus, and the telescope is properly focused on the rod. Each person’s eyes focus slightly differently, and these adjustments should be made each time you take an instrument out to use it.

5. There are also two other marks on the vertical crosshair called stadia lines. These are used for distance measurement and are not used in leveling. Be careful not to line your eye up with either of these when taking a reading (Figure 1).

6. The rod is not held plumb. If the rod is not plumb, the result will be a reading that is a higher number on the rod than the correct reading. The way to avoid this is to give the rod-person a signal to slowly pivot the rod forward and backward over the center point while holding it plumb to the vertical crosshair, and then record the lowest reading.

7. The rod-person can contribute to error by holding the rod at the wrong location, or by choosing a spot that is not stable. Good communication with the rod-person is the best way to avoid this type of error.





1. List three reasons why an instrument may not be level to the line of sight.

2. In order to compensate for error in an instrument where should the instrument be positioned when taking readings with it?

3. When the rod is not held plumb but is aligned with the vertical crosshair, the value of a reading taken will be:

a. higher

b. lower

4. List three ways that a rod-person can contribute to error.


Notes


Learning Task 4 Describe Setting up, Leveling and Testing an Optical Level

Tripod Setup Extend the legs so that the tripod head is level and the instrument will be at a comfortable height for readings. Snug their locking screws up, but do not over tighten the screws.

If possible, setup midway between the backsight and foresight locations.

Spread the tripod legs about 900 mm (3 ft) apart and set the feet firmly into the ground (farther apart if windy). If the ground is sloping, put two of the legs on the downhill side. Use a triangular wooden frame if setting up on a floor with a smooth surface such as concrete, where the feet of the tripod cannot dig in.

Make sure the tripod is secure against any movement by grasping the head and gently trying to move it in a horizontal circle. If there is any movement, then something is loose and all connections should be tightened up before proceeding to mount the instrument.

Attach the instrument to the tripod. Tighten the locking screw firmly, but do not over tighten.

Leveling the Instrument Leveling instruments are used to set, transfer and measure elevations. Leveling the instrument so that the line of sight is in a level position is the most important procedure to obtain accurate leveling work.

If the instrument goes out of level for any reason, it must be re-adjusted to a level position before continuing to take readings.

Leveling Instruments with Three Leveling Screws Instruments with three foot screws are quite different from those with four foot screws. The foot screws on a three screw instrument always hold the instrument from rocking so they do not need to be tightened up.

Instruments with three foot screws usually have two sets of leveling devices: a rough leveling device, which is usually a fish-eye bubble; and a fine leveling device, which is an automatically adjusting hanging prism.

Notes



The foot screws on three screw levels do not snug up. But it is possible to turn them all the way to the end of their travel, and this will give you the feeling that they are not able to turn any more. To allow full movement of the foot screws, position each of the foot screws half way in its travel prior to attempting to level the instrument. There is often a mark used to indicate half way.

Adjusting a Fish Eye Bubble Fish eye bubbles are always used for getting the instrument roughly level.

Adjusting a fish eye bubble can be frustrating because it is possible to “chase” the bubble around and around the vial until the travel of the foot screws is exhausted. To prevent frustration, choose one foot screw, and do not adjust it at all during the leveling process.

INSTRUMENT

BASE

ORIGINAL

BUBBLE

POSITION

FINAL

BUBBLE

POSITION

FIRST

ADJUST THIS

FOOT SCREW TO

RAISE THIS

CORNER OF THE

INSTRUMENT

SECOND

ADJUST THIS

FOOT SCREW TO

RAISE THIS

CORNER OF THE

INSTRUMENT

DO NOT

ADJUST THIS

FOOT SCREW

Figure 1. Leveling an instrument with three foot screws and a fish eye bubble

First look at the position of the bubble and adjust the foot screw to raise the corner of the instrument that seems to be opposite the bubble’s position. When the bubble is half way across the circle adjust the foot screw to raise the corner of the instrument that is now opposite the bubble’s position. Fine adjust the two foot screws to position the bubble. Remember to only adjust two of the three foot screws. With practice, rough leveling can also be accomplished by adjusting the tripod legs.


Notes


Testing the Accuracy of an Optical Level You should always test optical leveling equipment for accuracy before measuring or setting elevations. Even with all of the leveling devices adjusted correctly the instrument may still not be able to accurately transfer elevations. The cause of error at this point is the accuracy of the crosshair position. The “reticule” that holds the crosshairs can be adjusted up or down and left or right to correctly position the crosshairs in the image.

CROSS HAIRS SET CORRECTLY

CROSS HAIRS SET TOO HIGH

LINE OF SIGHT

LINE OF SIGHT

Figure 2. Error caused by incorrectly set crosshairs

Figure 2 shows two telescopes set exactly level, the upper telescope has the crosshairs set correctly, the lower telescope has the crosshairs set too high. The only way to check the position of the crosshairs at the job site is to do a “peg test” on the instrument.

Adjustment of the crosshairs is done by turning the crosshair adjustment screws. These screws are normally located under a cover just behind the eyepiece. Consult the owner’s manual before trying to adjust the crosshairs or send the instrument to a survey equipment repair shop for adjustment.

Testing the Accuracy of Leveling Instruments Using a Peg Test The basic principal of a peg test is that a leveling instrument will accurately transfer elevations if the distance from the instrument to the rod is kept constant regardless of whether the crosshairs are accurately positioned or not. This fact is why it is always best to have the distance to the rod for all sights be the same.

Peg Test Procedure

1. Set two pegs firmly into the ground about 60 m apart and position the instrument to be checked exactly in the middle of the two pegs as shown in Figure 3. It is very important to hold the rods plumb while taking the readings so that the distance to the rod from the instrument is exactly the same.

Notes



Figure 3.

2. With the instrument set up in the middle, take a reading on Station B and on Station D.

3. With the instrument set up at Station A, take readings on Station B and on Station D.

4. Subtract the first B reading from the second B reading and find the difference.

5. Subtract the first D reading from the second D reading and find the difference.

6. The two differences should be the same because the two pegs have not moved up or down. If the two differences are not the same, the crosshairs are not accurately set.

7. If the two differences are not the same, subtract one from the other and divide by 2 to find the error over 30 metres (as the second reading was taken over 60 metres).

Obtaining perfect results is not always practical; a maximum error of 6 mm or �⁄�” over 30 metres is usually considered to be acceptable on the peg test.





1. What device should be used with the tripod when setting up on a floor with a smooth surface?

2. Describe setting up and leveling an automatic level.

3. How do automatic levels automatically adjust the line of sight to level?

4. Explain how to check an instrument for accuracy by using a peg test.

Notes



Learning Task 5Review Setting and Measuring Elevations Using Optical Levels

The measuring and setting of elevations at a construction site must be done accurately and to the exact specifications shown on the construction drawings. Maintaining a record of how the elevations were set and who set them is also of prime importance. Using a surveyor’s field book to record all of the instances where elevations were measured or set allows a permanent record of the results to be kept.

The surveyor’s field book is a small hard covered book that is 4�⁄� inches by 7�⁄� inches in size. There are many types of field books; the standard field book used for leveling has six columns on both sides. Some field books have level notes on the left and a grid or graph paper on the right. The grid paper is used to make plan views of horizontal layout using a transit or theodolite.

Each page in the leveling field book is divided into 6 columns and 32 rows. The lines on the pages are printed with waterproof ink. When recording instrument readings into the field book, use a pencil, not a pen. The ink from a pen may not be waterproof.

Readings should never be erased once they have been recorded. After a second look, if a reading needs to be changed, cross out the initial reading and put the new reading above it. By leaving the initial reading in the book it shows that there was some concern with that reading.

STA BS HI IFS FS ELEV

Figure 1. Sample of a surveyor’s field book

The headings across the top of the pages should always be set up in the same way. The layout of headings shown in Figure 1 is the standard layout.


Notes


Glossary of Leveling Terms

Benchmark (BM) The benchmark is listed first in this glossary because it is the starting point for all leveling. Before any elevation can be measured or set, a benchmark must be found to refer the elevations to.

Local benchmarks, used for residential projects, are assigned an arbitrary value. 100.000 m or 100.00 feet are common values for a local benchmark. A large number is used to eliminate the possibility of any parts of the building having negative elevations in relation to the benchmark.

Elevations for commercial projects are usually referenced to a benchmark located off the construction site. The benchmark is usually referenced to a government datum, either the Geodetic Survey of Canada (GSC) or a municipal datum. A “datum” is a series of benchmarks all referenced to one point. The GSC for instance will reference their benchmarks, often called monuments, to the mean sea level.

The GSC monument may be some distance from the construction site. For this reason, the superintendent will establish a temporary benchmark (TBM) at the construction site. This TBM is used to set and measure elevations at the site. And because the TBM is referenced to the GSC datum, the elevations on the project will be set to GSC datum.

All BMs or TBMs should be established as relatively permanent points, with their locations clearly marked and protected from workers or machinery.

Field book records should precisely identify benchmarks so that they can be relocated if required in years to come.

Station (STA) The station is the name given to the spot where the rod is being held while a reading is being taken. The station is NOT where the instrument is set up. In Figure 2 the numbers in the circles do not indicate stations, the stations are BM, A, B, C and D.

Backsight (BS) A backsight is a reading taken on a point of known elevation. Since a survey progresses from a point of known elevation to points of unknown elevation, a backsight is a reading looking “backward” along the line of progress.

The first reading of any survey job will be a backsight onto a fixed point of reference, usually a benchmark.

Notes



Turning Point (TP) When moving the instrument to a new location, a turning point (TP) is set.

The point chosen for the TP must be visible from the new instrument location and must have a prominent point for the leveling rod to rest upon. Often a mark on the road is used. Once the TP is established, the survey rod is held on it. A foresight reading is taken and the elevation of the TP is calculated.

The instrument is then moved to the new location, leveled, and a backsight reading is taken on the TP. The leveling rod must be held in exactly the same point on a TP for both the foresight and backsight readings to ensure that the transfer of elevation is accurate. The backsight reading is added to the elevation of the TP to obtain the new elevation of the line of sight.

Height of Instrument (HI) The height of instrument is the “elevation” of the line of sight of the instrument relative to the datum of the BM.

The first step in any leveling work is to determine the height of the instrument. The elevation of the HI is found by taking a reading on a point of known elevation, usually a BM or TBM, and applying that reading to the elevation of the point.

Foresights (FS) and Intermediate Foresights (IFS) Foresight readings and intermediate foresight readings are readings taken on points of unknown elevation. The foresight readings are used to determine the elevation of a turning point or the elevation of the final point in a survey.

Intermediate foresight readings are booked under the IFS column to keep them separate from the foresights. This allows a math check to be done when the circuit is complete.

Elevation (ELEV) The elevation of a point is different than the height of the point. The elevation of a point or object is the distance that that point or object is above or below the referenced datum point.


Notes


Recording Elevations The following example is an attempt to create a real job site leveling problem to demonstrate the fundamentals of a leveling circuit.

Figure 2 shows the locations of the instrument, benchmark and stations, plus the rods for each sighting.

Figure 2. Schematic drawing of the level circuit and rod readings

Notes



Stn. BS+ HI IFS- FS- ElevationBM 0.527 100.527 100.000 m

A 100.527 0.923 99.604

B 100.527 <0.945> 101.472

C 100.527 2.780 97.747

C 1.810 99.557 97.747

D 99.557 <1.988> 101.545

Figure 3. Field book notes for the previous example

Using 100.000 m for the benchmark (BM), a backsight was taken on the BM to determine the height of instrument (HI).

This height was used for the next three sightings. As station “A” is lower than the HI, rod reading #2 is subtracted from the HI to get the elevation for “A”. As “B” is above the HI, the rod reading #3 is added to the HI.

Station “C” is a turning point. Once its elevation is determined as 97.747, a backsight from the new location can be taken. By adding the backsight to 97.747, the new height of instrument is found. It is then used with rod reading #6 to find the elevation of station “D”.

To help protect against errors, inverted readings should be enclosed in brackets.

Calculate Math Check

The backsight readings and the foresight readings were added up and the difference calculated. The elevation for the BM was subtracted from the final elevation “D,” and the difference compared with the previous difference. The two differences were exactly equal, so the arithmetic checked out. The math check only checks to see if the adding and subtracting was done correctly, it does not determine if the readings were taken correctly. It is the closing of the circuit on a point of known elevation that checks the accuracy of the leveling work.

(0.527 + 1.810) – (2.780 – 1.988) = 1.545

101.545 – 100.000 = 1.545

Figure 4. Math check


Notes


Exercise 1• Figure 5 shows a schematic diagram and some sample rod readings.

• Use the information contained in them to fill in the field book page in Figure 6 on the next page. Show your check to see if the math is correct.

• Note that the numbers on the schematic diagram represent corresponding numbered rod sections, and that BM elevation = 100.000 m.

Figure 5. Schematic diagram and rod sections

Notes



STA BS HI IFS FS ELEV BM 100.000 m

Figure 6. Field book page for Exercise 1





1. Explain why readings should not be erased and corrected in level note books.

2. Why is 100.000 m often used as a local benchmark?

3. What does a datum refer to?

4. What do the following abbreviations stand for?

IFS _______________________

BM _______________________

HI _______________________

STA _______________________

FS _______________________

5. What is the rod reading in Figure 1?

6. What is the rod reading in Figure 2?

Figure 1 Figure 2

Notes



Learning Task 6Identify Parts and Describe Use of Laser and Electronic LevelsLaser and electronic levels are easy to use. One worker can perform the same job as two using an optical level. Optical levels also allow many workers on large jobs to use the same instrument setup at one time with different receivers. Laser levels are ideal for setting suspended ceilings, leveling concrete floors, setting drain pipes, grading roads and building lots, and for other jobs that are usually done with a standard optical level.

It is important to read the manufacturer’s instructions before using these levels. Do not exceed the maximum range of the instrument and complete an accuracy check on a regular basis.

Laser LevelsLaser is a name derived from Light Amplification by Simulated Emission of Radiation (LASER). A mixture of helium and neon gases is used to emit a very narrow beam of light that does not grow larger as it moves away from the source, which is the laser level. The beam can be directed to any point or it can be rotated continuously at various speeds. The laser beam can be seen as bright red in low light conditions. In bright sunlight, a sensor or detector is required to read the beam. A laser level is shown in Figure 1.

WARNING!

Do not look directly into a laser beam! Looking directly into the beam may be hazardous to your eyes. A quick flash of the beam is not a problem, but avoid prolonged contact with your eyes. The instrument must be positioned either above or below the line-of-sight of the worker.

Figure 1. Laser level (Courtesy of Cansel Survey Equipment)


Notes


Electronic LevelsElectronic levels as shown in Figure 2 are very similar to laser levels, but they emit infrared rays that cannot be seen. A beam detector or sensor must be used to locate this infrared ray.

Figure 2. Electronic level (Courtesy of Cansel Survey Equipment)

Lasers and electronic levels depend on an electrical power source such as batteries, a 12 volt source from a truck or car, or a 110 VAC adapter.

Setup is very easy. A bubble level or fish-eye is used to rough level the instrument. When the bubble is in the ring, the instrument levels itself with its motor-driver leveling system. If, during operation, the instrument is knocked and moved beyond the limits of self-leveling, the beam shuts off.

The instruments can be supported in several ways. The most usual supports are tripods of various heights. They can also be clamped to columns, or have small feet attached so that they can be set into or on drainage pipes. Suspension frames are available to hold the instruments and aim them into pipes.

Notes



Sensors or Detectors Laser and electronic leveling instruments can be operated by a single person. When the instrument is set up and running, a level reference plane is created that can be detected with the sensor or detector (Figure 3).

Figure 3. Sensor or detector to locate an electronic beam (Courtesy of Cansel Survey Equipment)

The sensors or detectors operate on batteries and have a narrow window through which the beam can be detected. When the beam is sensed, the detector shows a small, coloured light or emits a sound. Sensors or detectors can be attached to the leveling rod or can be used by themselves to locate instrument height on walls or forms.

Targets Targets are made of clear plastic with a cross marked on them. They are used to set levels with a laser level for items such as ceiling T-bars, concrete screeds or drainage pipes, using a direct or rotating beam. The object (with target attached) is lowered, raised or moved sideways until the beam is located at the target cross.


Notes


Setup Procedures Select the location for the instrument so that the largest possible area can be covered.

The location should be on solid ground or floor, and out of the way of traffic.

1. Set up the tripod and attach the instrument. Level the instrument with the leveling screws until the bubble is in the centre circle.

2. Connect the power supply to the instrument, and turn the power switch on.

3. Using a level rod, establish the height of the instrument from the bench mark.

4. Calculate the vertical distance between the instrument and the point whose elevation you wish to find.

5. Attach the sensor or detector to the level rod at this mark.

6. If the elevation to be measured is higher than the instrument, hold the rod upside down. If it is lower than the instrument, hold the rod upright.

7. Raise or lower the level rod until the sensor indicates the correct level. Mark the end of the level rod at each location where elevations are required.

8. An alternative method is to mark the location of the beam directly on the wall, concrete form or column. Then measure up or down the required amount to establish the correct elevations.

Laser Level Accuracy CheckMany laser levels are designed to allow the operator to calibrate the unit. The manufacturer’s instructions will include the method.

Often it is a simple as setting up 50 metres from a wall, marking the location and then rotating the instrument 360° and marking again. If the two marks are not within tolerance of each other, then turn the instrument on by pushing two buttons at once, and adjust the beam up or down by pushing buttons. Then rotate the instrument 90° and make a third mark. Rotate the instrument another 180° and make a fourth mark. The instrument is turned on by pushing another combination of buttons, and then the beam is adjusted. In this way, both the X and Y axis are recalibrated.

Pipe Laser LevelsPipe laser levels are specially designed for installing pipes requiring a constant grade and for setting grades for areas requiring drainage.

In laying pipe, the laser is set up at the end of the pipe (either inside or on top) and set to the desired slope of the pipe. The target is located at the end of the pipe and the pipe is moved until the target is centred to the beam. Pipe laying can continue until a change of direction is required, or the maximum range of the beam has been reached.

Notes



Five-way Laser LevelsA five-way laser level is used mainly for laying out 90 degree corners, for leveling, and for plumbing up or down. It can also be used as an electronic caulk line. There are five laser beams; one shoots down, one shoots up, one shoots straight forward. The last two are at 90° on both sides to the forward beam.

The unit self-levels, and the beams are bright enough that a sensor is not required. Most five-way levels are accurate only up to between 10 and 30 metres, as the laser beam becomes too wide past that point.

Five-way laser levels can be set on the floor, mounted on a tripod or clamped to an object. Follow manufacturer’s instructions; be careful not to exceed the rated distance. As the laser beams are quite bright, extra care should be taken not look into the beams.





1. What kind of beam does an electronic level have?

2. Sensors or detectors are not required for locating the beam of a laser or electronic level.

a. true

b. false

3. If the instrument is knocked and slightly moved, the beam will continue to be aimed correctly.

a. true

b. false

4. Which beam cannot be seen, the laser or infrared?

5. Laser or electronic levels are not suitable for use when laying drainage pipes.

a. true

b. false

6. Looking directly into the beam can be hazardous to your eyesight.

a. true

b. false

7. A five-way laser level is a good choice for setting foundation wall heights.

a. true

b. false

british columbia carpenter apprenticeship program · the transit level (courtesy of cansel ... the...

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