Surveying Equipments

Level Rods:

  Leveling rods are commonly made of three types of material; wood, typically hard maple, fiberglass or aluminum. Aluminum can swell or contract in hot or cold weather, wood can expand or contract in humid or wet conditions and can give inaccurate readings.

        Rods should be held by the edges and without touching the numbers. Touching the numbers may wear down the face of the rod, giving inaccurate readings. The bottom of the rod should never be dragged on the ground or through water, grass or mud and its metal base should never be allowed to strike rocks, pavement or other hard objects; which will gradually wear away the metal base and will cause leveling errors due to the change in length of the rod itself.

Direct Reading Rods

       Direct reading rods are rods that are read directly through the telescope of the person using the instrument. Another name for these rods is self-reading rods.

 Philadelphia Level Rod

          A philadelphia level rod consists of two sliding sections graduated in hundredths of a foot and joined by brass sleeves. Two sections make it easier to transport. Can be used as a short rod for readings of 7' or less, to a long rod for heights up to 13'. It has a rear section that slides on the front section. When a high rod is needed, the rod must be fully extended, otherwise a serious mistake will result in the reading. Graduations on the front faces of the two sections read continuously from 0–13'. A Philadelphia rod can be read accurately with a level at distances up to 250'.

San Francisco Level Rod

      A san francisco level rod is similar to the Philly rod; the San Francisco rod has three separate sections that slide past each other to extend or compress its length, and is generally used on control, land and other surveys.

Direct Elevation Rod or a “Lenker Rod”

    A Direct Elevation Rod or a “Lenker Rod” has numbers in reverse order on an endless graduated strip that revolves around the rod on rollers. Figures run down the rod and can be brought to a desired reading—for example the elevation of a point or benchmark. Rod readings are preset for the backsight, and then, due to the reverse order of numbers, foresight readings give elevations directly without calculating backsights and foresights.

Target Rod

    A target is added to the rod that allows the person holding the rod to independently check the readings taken by the person using the instrument by adding a target, making what is commonly referred to as “target rod.”

Tripods

       A sturdy tripod in good condition is essential for obtaining accurate measurements. The legs of the tripod are adjustable and are made of wood, fiberglass or aluminium and are adjustable for use with many different pieces of surveying equipment. Tripods made of wood or aluminum can influence readings in certain weather conditions, fiberglass can be heavy to carry when surveying over various terrains and distances. Tripods come with two different styles of heads: flat or dome. Dome heads allow for more adjustment, flat head tripods have less play, but are sometimes easier to fit. Tripods come in two different thread sizes: 3" x 8 and 5⁄8" x 11. 5⁄8" x 11 is standard for newer equipment. Adapters are available to adapt older 3" x 8 tripod threads to 5⁄8" x 11.

Hand Level

     A hand Level is used for taping and rough determination of elevations. It consists of a metal sighting tube with a bubble tube mounted on it. The bubble is located on the top of the instrument and its image is reflected by means of a 45° mirror or prism inside the tube so that the user can see the bubble at the same time as the terrain. If the bubble is centered between the horizontal lines in the tube while sighting, the line of sight is horizontal.

Abney Level

        An abney level functions as a hand level and also permits rough measurements of vertical angles and slopes.

Automatic Levels

        Automatic levels are commonly used in today’s surveying or construction applications because of their ease of us and quick set-up. They incorporate a self-leveling feature; the user rough levels the instrument using a three-screw leveling head and centers a bull’s eye bubble. After the bubble is manually centered, an automatic compensator takes over, levels the line of sight, and keeps it level so that level horizontal measurements can be taken.

Electronic or Laser Levels

    Electronic or laser levels transmit beams of either visible laser or invisible infrared light. These levels are used for establishing a known reference elevation or a point where construction measurements can be taken. Electronic or laser levels fall into two general classes: single-beam lasers and rotating-beam lasers. A single beam laser projects a string line that can be projected in a vertical, horizontal or inclined direction. A rotating beam laser provides a plane of reference over open areas. The laser beam is selfleveling and will not come on until the instrument is level. If it is bumped out of position, the beam shuts off and will not come back on until it is level again. Laser levels are precise up to 1000'. Common uses include grading and excavating, masonry work, setting concrete forms, marking elevation, septic work and checking the depth of trenches.

Laser Detector

               A laser detector is necessary because not all laser levels incorporate a visible laser; and, lasers are not typically visible to the human eye in bright sunlight. The detector can either be a small hand-held or rod-mounted unit that may be moved up and down the level rod, alerting the user when it is level.

Double Pentagonal Prism

    A double pentagonal prism is hand-held instrument that determines right angles by the use of a triangular-shaped prism.

Measuring Wheels

     Measuring wheels can roughly measure distance by rolling a wheel along the line in question and counting the number of revolutions. An attached odometer does the counting and from the circumference of the wheel converts the number of revolutions to a distance. Measuring wheels typically provide precision to 1⁄200 when the ground is smooth, such as along a highway, but results are poorer when the surface is irregular.

Tapes or “Chains”

       Tapes or “Chains”  measure distance by using steel tape typically 0–3⁄8" wide. Those graduated in feet come in 100, 200, 300 and 500' length. Metric tapes/chains have standard lengths of 30, 60, 100 and 150 meters. All tapes can be wound on a reel (sold separately) or done up in loops. Tapes/chains are typically handled with tension handles or clamp handles in order to apply tension and to prevent damage to the tape and the surveyor’s hands. Tapes/chains used for surveying applications are required to be calibrated on an annual basis to ensure accuracy.

Taping or Chaining Pins

       Taping or Chaining Pins are used to mark tape lengths. Most chaining/taping pins are made of number 12 steel wire, sharply pointed at one end and have a round loop at the other end. They are painted with alternate red and white bands. A steel ring with 11 pins is standard.

Range Poles

         Range poles are used in taping applications for sighting points, marking ground points and for lining up surveyors in order to keep them working in the right direction. They are from 6–10'L and are painted with alternate bands of red and white to make them more easily seen. Each band is 1'L and the rods can be used for rough measurements Poles can be wood, fiberglass or metal.

Plumb Bobs

     Plumb bobs are typically made of brass (to limit interference with compass readings) and weigh from 6–18 oz., with a fine point. The point on all plumb bobs are standard, to make replacement easy. At least 6' of good quality string or cord, free of knots, is necessary. Bobs are used to get a “plumb” (straight) vertical line to a definite point, typically a tack in a wooden stake or ground. Bigger/heavier plumb bobs should be used for higher or greater heights.

Gammon Reel

         A gammon reel is the device used to connect to plumb bob and provide easy up-and-down adjustment of the plumb bob and instant rewinding of the plumb bob string. The gammon reel can also be used as a target when taping.

Transits/Theodolites

           Transits/theodolites are fundamentally the same. Their most important application is measuring horizontal and vertical angles, but they can also be used to obtain horizontal distances and determine elevations. Transits/theodolites can be used for surveying applications when used with a calibrated taping chain or an electronic distance measurer.

Electronic Distance Measurers (EDMs)

      Electronic distance measurers accurately measure distance by measuring the time it takes a laser to travel from the EDM to a prism and back. Before the introduction of EDMs, taping or chaining was used to make accurate distance measurements.

Total Station

          A total station is the most accurate surveying device because it incorporates an electronic or digital theodolite, an electronic distance measuring (EDM) device and a microprocessor in the same unit. Total stations can automatically measure horizontal and vertical angles as well as slope distances from a single setup. From this data they can instantaneously compute horizontal and vertical distance components, elevations and coordinates, and display the results on an LCD. They can also store the data either on board or in external date collectors. From the total station, data can be downloaded easily to a personal computer.

Global Positioning Systems (GPS)

    Global positioning systems incorporate distance, direction and difference in height between survey points. A GPS satellite surveying system simply using an electronic distance measurer that does not need direct line of sight between survey points. Instead, a GPS receiver needs to have a direct line of sight to a sufficient number of satellites.