Calibration Of Surveying Instruments Tools: A Case Of Automated Total Station In Southern California's Water Reservoir

Equipment Used In The Project

Discuss About The Calibration Of Surveying Instruments Tools.

Engineering surveying is one type of survey that is very crucial in any construction project as it helps in collecting data about the exact positions of natural and manmade resources, which is essential when designing any engineering project. The data and information collected by engineering surveyors is usually used in developing practical designs of structures such as dams, bridges, railways, ports, irrigation systems, water reservoirs, ports, tunnels, sewer lines, etc. [1]. The design of almost all civil engineering projects depends on data gathered by surveyors. Without engineering surveying, the society would be greatly chaotic and disorganized as structures would be constructed without any proper planning. Therefore besides aiding in accurate design of structures, surveying also helps in ensuring proper planning of the society [2].

There has been a lot of development over the past decades on how surveying is done. Today, surveyors use specialized equipment and technology, which has improved accuracy and speed of surveying. Total station is one of the widely used and most preferred engineering surveying equipment in the civil engineering field today, mainly because of its high accuracy [3]. This instrument is used for measuring angles across vertical and horizontal planes. It also evaluates relative terrestrial distances using a built-in electronic distance measurement (EDM) device. This essay presents a report on how an automated total station was used in Southern California’s water reservoir. 

The Southern California's water reservoir is one of the largest water storage facilities in California and its main purpose was to help in solving the water shortage cases. The dam incorporates 3 earthen dams and will be of benefit to the Californians as well as the Los Angeles residents. The stability, deformation monuments, reservoir filling of the dams are monitored by the help of an automatic survey system [4]. Total stations were erected in this project to assist in the detection of points which have been displaced and are larger than 10mm.  The operation of the total station is purely automated and they will gather data on the three-dimensional basis in relation to the set time. Besides, they are connected to a GPS system which is programmed to put the total station on every time there is an overshoot in the tolerance level as a result of abrupt settlement [5].

Typically, the personnel involved in using a total station are the operator and rod operator (assistant staff). The assistant staff is the member who holds a survey pole fixed with a reflective prism and bubble level for ensuring that the pole is vertically straight. Some of the end-users of total stations are land surveyors, archeologists, crime scene investigators, miners, water companies, etc. In this project, the total station was used to monitor the stability and variations of water levels in the Southern California’s water reservoir. Since the total station was robotic ad automated, there was no personnel interacting with the equipment physically as it automatically send the data collected to computers in the company office. The equipment was controlled using an electronic remote.

Personnel and End-users

The total station contains very delicate instruments hence when it is being operated it should be handled with a lot of care. The transportation, packing, and removal of the total stations should be carefully done. The settling over the station mark of the total station is done by the following procedures: centering, leveling [6], and parallax removal. Entries which are made through the inbuilt keyboards are used in controlling the total station.

The equipment used was the meteorological sensors and robotic total stations. It is calibrated in such a way that the nominal distance standard deviation for a single measurement is ±2 mm ±2 ppm with a standard deviation in the direction of ±1 arc second. For units which have applied the S designation, they have similar deviation. The calibration system of the total station is by laser measuring system, which has very high precision [7].

The following are some of the activities involved in the maintenance of a total station:

Lifting – the lifting of the total stations from the case should be done with both hands whereby the base and the knob will be ripped. Besides, a tripod and tribrach lock would be engaged to ensure that the instrument if firmly secured

Carrying tripod – when the total station is removed, it should be recessed for transportation purposes. Besides, it should be carried in a vertical position with the legs of the tripod pointing downwards.

Adjusting collimation – the instrument should be adjusted once the collimation error has been established to be consistent with an excess of 10 seconds or 20 seconds. This adjustment should only be done by a trained personnel. 

The battery and other components of the total station should also be checked frequently by a trained and certified technician.

The specifications provide the procedures and methods which are required to achieve a certain accuracy in surveying. Or instance, under the regulations and standards.

A total station has a tolerance setting that allows the user to adjust tolerances depending on the accuracy requirements of the project [8]. The tolerances of the total station were as follows: horizontal angle/observation tolerance – 30 seconds; vertical angle/observation tolerance – 30 seconds; EDM or distance tolerance – 2 millimeters; and stakeout tolerance – 0.3 feet. Standard deviation for each measurement was not allowed to exceed these tolerances.

This refers to the sense of vertical or horizontal reference system. For a total station equipment, the horizontal datum is localized as a planar with regards to the bearing by the application of ellipsoid models while for the vertical datum, the total station applies optometric datum.

Operation

The legislation governing the use of total station is California Survey Law. The applicable legislations include: Professional Land Surveyors (PLS) Act (Business and professional code 8700-8805) [9], subdivision map act (government code 66410-66499.58) and board rules (civil code 400-476). This legislation has provisions guiding land surveying profession. Therefore all engineering surveying activities must be done in accordance with this legislation.

According to California Survey Law, surveying can only be done by a trained and licensed professional. This means that the total station must be used by qualified personnel. The total station should also be purchased from reputable and certified manufacturers. At the time of use of the total station, it should be in good working condition. The survey reports must be shared with the relevant department or local authorities for approval. Last but not least, any surveyor who commits an offense against this regulations will be subject to disciplinary proceedings [10].

The collection of data of the dam comprises of taking radial shots both in the reverse and direct mode and this applies to three reference points as well as the object prisms, in the vertical and the horizontal directions. Each of the total stations contains a subset reference and it is treated as a sub-network in the next phase of data processing and analysis. By the help of a connection cable, the total stations are connected to a computer system which controls and displays all the functions automatically. Besides, there will be a preset time that the system will operate based on. All the total stations are programmed to gather a certain number of required shots at various angle and time intervals for purposes of accuracy.

There are some accessories which help in the capturing and management of the data which is obtained from the totals station. They include: tripods for holding the total stations; tribrachs – which helps in achieving the accuracy; reflectors – these are high-quality glass for coating and longevity; batteries – which powers the instrument; micro SD storage system for storing the data collected; data transfer cables; bags and carriers for securing the instruments; wye piece lenses for highest performance; poles for the stability of weight; and carriers for high accuracy [11].

A total station processes and analyzes surveyed data using computational methods. The computations are done using an external device known as data logger or data collector. The device is designed such that it keeps records of all the data that is being analyzed. It also has an inbuilt microprocessor for data processing. The microprocessor has the capability of averaging numerous observations. It can compute x-y-z coordinates and horizontal distance using horizontal and vertical angle measurements, slope distance measurement, and instrument and target height measurements. The total station can also be integrated with Global Navigation Satellite System that is used to measure coordinates of the surveyed points. Additionally, total stations are equipped with Geographic Information System (GIS) and Global Positioning System (GPS) that enables precise mapping of the points that are being surveyed [12].

Calibration

A total station presents data using electronic display. The operator has to press respective keys depending on the data he/she wants displayed. The equipment can display horizontal & vertical distances, horizontal & vertical angles, three coordinates of surveyed points; and elevation deviations between surveyed points [13]. It can also store the data in an electronic notebook or send it directly to a computer connected to it.

A total station is a real-time equipment integrated with an onboard computer that enables live feedback. The onboard computer uses real-time measurements to adjust or resolve data and set the desired construction points. This ensures that high quality and accuracy of the data collected by a total station.

References

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S. Padhi, "Working Knowledge of a Total Station - Essential Skill for Civil Engineering Students," Skyfi Labs, 24 May 2014. [Online]. Available: https://www.skyfilabs.com/blog/working-knowledge-of-a-total-station. [Accessed 13 May 2018].

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