Total Station 2016 625y6g

CE 6404 – SURVEYING II – UNIT III TOTAL STATION SURVEYING  Basic principle - Classifications.  Electro-optical system: Measuring principle, Working principle,

Sources of error.  Infrared and Laser Total Station instruments.  Microwave system: Measuring principle, Working principle, Sources

of error.  Microwave Total Station instruments.  Comparison between Electro-optical and Microwave system.  Care and maintenance of Total Station instruments.  Modern positioning systems - Traversing and Trilateration. CE6404_UNIT_III

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MODERN SURVEYING INSTRUMENTS • As an outcome of continuous technological development, in the last few decades, new varieties of electronic instruments have been invented for surveying and with these inventions, modern surveying practices came into existence. • Hence with modern surveying instruments, survey work will be precise, faster and less tedious. • All the readings are recorded automatically by the electronic instruments in a microprocessor and based on these readings; critical values are calculated by the microprocessor, at real time. Hence, the data collected in microprocessor is directly transferred and stored in the computer as a softcopy. • Modern surveying instruments are becoming more popular and they are gradually replacing old surveying instruments such as Com and Dumpy level.

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Total station

EDMI

Digital level

Auto level

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ELECTRONIC DISTANCE MEASURING INSTRUMENT (EDMI) • EDMIs were first introduced in 1950's by Geodimeter Inc. • Early instruments were large, heavy, complicated and expensive. • Improvements in electronics have given lighter, simpler, and less expensive instruments. • EDMIs can be manufactured for use with theodolites (both digital and optical) or as an independent unit. These can be mounted on standard units or theodolites or can also be tribrach mounted. • The electronic methods depend on the value of velocity of Electromagnetic radiation (EMR), which itself is dependent upon measurement of distance and time. • Hence, there is no inherent improvement in absolute accuracy by these methods. The advantage is mainly functional - precise linear measurement can now be used for longer base lines, field operations can be simplified and trilateration can replace or augment triangulation. CE6404_UNIT_III

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PRINCIPLE OF EDMI • The general principle involves sending a modulated Electro-magnetic (EM) beam from one transmitter at the master station to a reflector at the remote station and receiving it back at the master station. • The instrument measures slope distance between transmitter and receiver by modulating the continuous carrier wave at different frequencies, and then measuring the phase difference at the master station between the outgoing and the incoming signals. • This establishes the following relationship for a double distance (2D).

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Where m is unknown integer number of complete wavelengths contained within double distance, Φ is the measured phase difference and λ is modulation wavelength, and k is constant. Multiple modulation frequencies are used to evaluate , the ambiguity.

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• Various EDMIs in use are based on two methods: –

using timed pulse techniques such as those used in variety of radar instruments.

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using measurements of a phase difference which may be equated to one part of a cycle expressed in units of time or length.

• Pulse methods have advantages over the phase difference methods but their weight and power requirement is such that they cannot be classed lightweight portable instruments. CE6404_UNIT_III

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PULSE TECHNIQUE • Such measurements incorporate a very precise measurement of time usually expressed in units of nanoseconds (1x10 -9 s), which a EM wave takes to travel from one station to another. • In this method, a short, intensive pulse radiation is transmitted to a reflector target, which is immediately transmitted back to the receiver. • The distance (D) is computed as the velocity of light (V) multiplied by half the time (Δt/2) the pulse took to travel back to the receiver (D = V X Δt/2).

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PHASE DIFFERENCE TECHNIQUE • The relationship between wavelength and associated phase difference shows that for a given complete cycle of EM wave, the phase difference can be expressed both in of angular (degrees) and linear (fraction of wavelengths) units. • In phase difference method used by majority of EDMI, the instrument measures the amount δλ by which the reflected signal is out of phase with the emitted signal.

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TOTAL STATION • The total station is an improvised version of modern surveying instruments such as EDMI, auto level and digital level. • Total station is a combination of an electronic theodolite and an Electronic Distance Meter (EDM). • This combination makes it possible to determine the coordinates of reflector by aligning the instrument’s cross hair on the reflector and simultaneously measuring the vertical and horizontal angles and slope distances. • On board micro-processor in the instrument takes care of recording readings and the necessary computations. The data can be easily transferred to a computer where it can be used to generate a map.

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FUNCTIONS OF TOTAL STATION • Coordinates determination: Total station determines the coordinates of an unknown point relative to the known coordinate by establishing a direct line of sight between the two points. Angles and distances are measured from the total station to points under survey and the coordinates of surveyed points relative to the total station position are calculated using trigonometry and triangulation. Some total stations have Global Navigation Satellite System (GNSS), which does not require direct line of sight to determine coordinates. •

Distance measurement: A total station has a small solid state emitter within the instrument’s optical path. They generate modulated microwave or infrared signals that are reflected by a prism reflector or the object under survey. The modulation pattern in the returning signal is read and interpreted by the computer in the total station. The distance is thus determined by emitting and receiving multiple frequencies and determining the integer number of wavelength, to the target, for each frequency.

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Angular measurement: Most of the modern total stations have digital bar-codes on rotating glass cylinder that are installed within the instrument. Angle measurements is done through electro-optical scanning of these digital bar-codes.

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Data processing: The data recorded by the instrument may be ed from the instrument to a computer and the application software in turn generates a map of the survey area. Many advanced models of total station have built-in micro-processor to record and compute distances, horizontal and vertical angles.

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ADVANTAGES OF TOTAL STATION • Most accurate and friendly. • Gives position of a point (x, y and z) w. r. t. known point (base point). • EDM is fitted inside the telescope. • Digital display. • On board memory to store data and compatibility with computers. • Measures distance and angles and displays coordinates, • Auto level compensator is available. • Can work in lesser visibility also. • Can measure distances even without prismatic target for lesser distances. • Is water proof. • On board software are available. • Total solution for surveying work.

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APPLICATIONS OF TOTAL STATION IN VARIETIES OF FIELDS: IN CIVIL ENGG. FIELD: • • •

Mainly used by land surveyors. Used by archaeologists to record excavations. By police, crime scene investigators, private accident re-constructionists and insurance companies to take measurements of scenes.

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• • • • •

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General purpose angle measurements. General purpose distance measurement. Provision of control surveys. Contour and detail mapping. Setting out and construction work.

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AUXILIARY EQUIPMENTS •

Targets or Prisms to accurately define the target point of a direction measurement.

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A data recorder if one is not integrated into the total station.

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A cable and software on a PC to capture and process the captured digital data to produce contour and detail maps.

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CLASSIFICATION OF TOTAL STATION • Wavelength used •

Working range

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Achievable accuracy

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