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Chapter:
1. purpose of total station
TOTAL STATION:
Total station is a surveying equipment which is the combination of Electromagnetic Distance Measuring Instrument and electronic theodolite mainly used by land surveyors and civil engineers, either to record features as in topographic surveying or to set out features (such as roads, houses or boundaries). It is also integrated with microprocessor, electronic data collector and storage system. The instrument can be used to measure horizontal and vertical angles as well as sloping distance of object to the instrument.
WORKING PRINCIPLE:
It measures angles, from a known point, similar to the traditional theodolite, but digitally.The internal mechanism is in the same way an EDM works with a laser and a sensor.The EDM measures distance between two points - the total station, and the prism which will be placed on an object/specific point of interest that you are surveying/setting out. After having the coordinates of known point, the total station will then fire a laser beam directly into the prism and the time that is taken for it to reach back to the total station (which has an in-built sensor) can gauge the distance very accurately if all the conditions are correct.
The position of the total station is then calculated by the software by means of triangulation when this process is repeated at a different coordinated station. Any error will be distributed between the two known points to ensure that accuracy is maintained.
FEATURES OF TOTAL STATIONS:
Some key features are:
Absolute circle reading
Audible notice for `90^0` turns
Connectivity to third party devices
Dual axis compensation for reliable horizontal and vertical reading
Electronic laser distance measurement
Excellent hardware features such as laser plummet, brilliant optics for `30x` magnification
Free set up possible sketch from Blueprint
Graphic sketches
High resolution LCD display
New and intuitive software
Unique levelling guidance for fast and convenient setup
It has the feature to enter the data at the office and simply call it up at the site.
It has the feature to upload and transfer data via board data connection.
It has the feature to edit and exchange data.
HINT: REMEMBER WITH ASCENDING LETTER
ADVANTAGES OF TOTAL STATION:
Field work is carried out very fast.
Accuracy of measurement is high.
Manual errors involved in reading and recording are eliminated.
Calculation of coordinates is very fast and accurate. Even corrections for temperature and pressure are automatically made.
Computers can be employed for map making and plotting contour and cross-sections. Contour intervals and scales can be changed in no time.
It offers automation of the old maps.
It provides a graphical view of plots and land for quick visualization.
It provides local language support.
 It has integrated database.
Data can be saved and transferred to a PC.
However, surveyor should check the working condition of the instruments before using. For this standard points may be located near survey office and before taking out instrument for field work, its working is checked by observing those standard points from the specified instrument station.
APPLICATION OF TOTAL STATION:
The total station can be used for the following purposes.
Detail survey i.e., data collection.
Control Survey (Traverse).
Height measurement (Remote elevation measurement- REM).
Fixing of missing pillars (or) Setting out (or) Stake out.
Resection.
Area calculations, etc.
Remote distance measurement (RDM) or Missing line measurement (MLM).
Mining :
Total stations are the primary survey instrument used in mining surveying. â?¢ A total station is used to record the absolute location of the tunnel walls, ceilings (backs), and floors as the drifts of an underground mine are driven. â?¢ The recorded data are then downloaded into a CAD program, and compared to the designed layout of the tunnel.
Mechanical and electrical constructionÂ
Total stations have become the highest standard for most forms of construction layout. â?¢ They are most often used in the X and Y axis to lay out the locations of penetrations out of the underground utilities into the foundation, between floors of a structure, as well as roofing penetrations.
Meteorology
Meteorologists also use total stations to track weather balloons for determining upper- level winds. â?¢ With the average ascent rate of the weather balloon known or assumed, the change in azimuth and elevation readings provided by the total station as it tracks the weather balloon over time are used to compute the wind speed and direction at different altitudes.
DISADVANTAGES OF TOTAL STATION:
The instrument is costlier than other conventional surveying instruments.
 It might be troublesome for the surveyor to investigate and check the work when surveying.
Working with total station is not so easy, as more skilled surveyors are required to conduct a total station survey.
To perform the work completely its needed to go back to the office and perform drawings with particular software.
Vertical elevation accuracy not as accurate as using conventional survey level and rod technique.
Horizontal coordinates are calculated on a rectangular grid system.However, the real world should be based on a spheroid and rectangular coordinates must be transformed to geographic coordinates if projects are large scale.
FIELD PROCEDURE:
Set up the TSS
Tripod Setup
Wipe off head to ensure that surface is clean and free of dirt
Extend all three legs equally prior to spreading the legs. Secure locking Mechanism
Spread the legs sufficiently to ensure a stable base for the tripod
Center tripod head over the point while maintaining a fairly level tripod head
Check centering by dropping pebble from the center of the tripod head. (within 2" of Pt)
Step down firmly on the footpads to set the legs
Instrument Setup
Secure instrument to tripod and center over tripod head
Bring all leveling screws to a neutral position, just below the line on the leveling screw post
While looking through optical plummet (if needed adjust o.p. for parallax and focus on the ground) or
with Laser plummet on, position instrument directly over point by using Leveling screws only.
Observe what two legs need to be adjusted to bring Bullseye bubble into the middle
Be careful not to move the third Leg
Release Horizontal tangent lock and rotate instrument until tubular level vial is parallel (in Line)Â to 2 of the leveling screws.(this position 1)
Rotate both leveling screws equal amounts in opposing directions until tubular level vial is centered
Rotate instrument until tubular level vial is perpendicular to Position 1
Rotate leveling screw equal until tubular level vial is centered
Re-observe the point with o.p or laser plummet an adjust instrument over the point by loosening the center screw and shifting instrument over the point and re-tighten screw.
Re-check the fine(tubular) bubble vial in position 1 and 2 and adjust as needed
Powering Up the Total Station:
Turn on the total station by pressing the red power supply switch (the red square button) once on the back of the total station. After the machine beeps, the display panel will display the message: "TURN SCOPE". Loosen the black telescope clamp screw (the smaller of a two-in-one knob located on the back of the total station directly above the power supply switch) by turning the knob counter-clockwise. Pivot the objective lens assembly vertically at least 90o until the "TURN SCOPE" message disappears. Now, re-tighten the telescope clamp screw and remove the lens cover protecting the objective lens.
Powering Up the Palmtop Computer
With the total station powered up, attach the palmtop computer to the mounting bracket on the tripod and plug the 9-pin female cable into the palmtop. Plug the other end of the cable (round slotted male connector) into the total station (The receptacle is located on the front of the total station just above the optical plummet eye piece).
Press the "ON" button in the upper right corner of the key pad. When the screen display shows the "Plant Records Mt. Cuba Center for the Study of Piedmont Flora", press the blue "FILER" key (this key contains the symbol of a filing card) in the upper left quadrant of the key pad.
Press the "PG DN" (Ã?) key in the upper right quadrant of the key pad until "bgmap.bat" is highlighted in black. Press the "ENTER" key. The next screen should be the "BG-Map Total Station Interface".
Computer/Total Station Alignment Setup
Enter the Setup mode by pressing the "S" key. The Setup Menu appears. Press the "U" key to select the units of measure and press the "f" (feet) key.
To begin setting the Station Coordinates, press the "S" key. You will be prompted with: "Coord? (#StationID)". Enter the IDnumber (ie. 2975) of the control point you have selected for your setup location preceded by the # sign; for example #2975 (This is the location where the total station is currently located). Press the "ENTER" key. Coordinates will appear next to the Station X and Station Y labels at the top of the page.
Next, press the "A" key to begin manually setting the horizontal angle. Enter the Idnumber (ie. 2973) of the control point where the prism is set up preceded by the # sign; for example #2973 (this is the other line-of-sight control point that will tell the total station where it is located). Press the "ENTER" key.
Write down or note the Azimuth; for example 18o 02' 50". You will use this information in Step #24 as you align the total station with the second control point. DO NOT press the space bar on the palmtop as instructed. Press "Q" to quit (the palmtop returns to the Setup Menu).
Now, return to the total station and release the black clamp screw (the smaller of a two-in-one knob located on the back side of the total station to the right of the square red power supply switch). Rotate the total station until the display panel reads an angle close to the Azimuth angle you wrote down in Step #23; in this example, 18o 02' 50". Tighten the clamp screw and turn the larger tangent screw knob on the two-in-one knob to make the necessary fine adjustment. Once you have the exact angle showing on the display panel, press the "H.HOLD" button on the back of the total station below the display panel TWICE. The angle has been locked into the total station memory.
Release the clamp screw so the total station can rotate. (NOTE: the angle will not change as the total station rotates.) Using the collimator (a crude sighting device) on the top of the total station instrument, align the total station with the prism. Utilizing the telescope tangent screw and the tangent screw, center the eyepiece lens vertically and horizontally on the prism with the cross hairs centered on the prism. Focus on the prism using the large focusing knob as necessary.
Now, with the total station aligned horizontally and vertically with the prism, press the "H.HOLD" button on the back of the total station below the display panel ONCE. This links the azimuth angle (in the example 18o 02' 50") on paper between the two control points, to the instrument in the field.
YOU ARE NOW READY TO BEGIN MAPPING PLANTS.