Leveling staff

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The leveling staff is a yardstick used in geodesy . It describes the perpendicular distance between the horizontal aiming beam of the leveling telescope and the point where the staff touches down, and it sets the vertical scale, especially for geometric leveling . In addition, it serves as a target point for a precisely leveled measuring device, the leveling instrument .

E-latte

introduction

In general, leveling staves are made of dried pine or ash wood, but a metallic construction is also possible. Their shape is rectangular with a width of 6–9 cm and a height of usually 3–4 m. In addition, ribs are often attached to stiffen and protect the slat division. There are handles on both sides of the bar for better handling. The versions of the leveling staff are very versatile: they can be folded in, can be put together from individual segments or as a telescopic staff. An oil paint and weatherproof varnish protect against moisture, a metallic foot fitting at right angles to the longitudinal axis of the slat with a flat surface against damage and it sets the zero point.

Types / construction methods

Different leveling staffs are used depending on the type and purpose of the application. They differ in terms of their graduation, material use and the achievable accuracy of the reading.

  • Leveling staffs

  • simple staff with E-graduation

  • Dual scale stick

  • Code bar

Simple lath (DIN 18703)

The simple staff is characterized by its relatively simple division of fields. Large Arabic numerals at the beginning of the corresponding field indicate the dm division. The cm division within a section is made clear by thick lines. Between these, the millimeter can only be determined by estimating. The change in color, usually red / white or black / white, reduces gross reading errors. The metric graduation of the lath is called E-graduation because of its appearance, hence the name E-latte. As a result of irradiation may lead to errors in the estimation millimeters. White fields on a black background appear larger than black on white. This effect is counteracted by the chessboard division in other designs of simple slats.

Precision staff (DIN 18717)

With the precision leveling, special precision staffs must be used. They also have a frame made of wood or light metal, but in contrast to simple slats, an invar strap is clamped with approx. 200 N tensile force. This achieves a high level of resistance to changes in length due to temperature fluctuations. A more differentiated scale division also increases the accuracy. On the one hand, the ½ cm graduation gives a more precise reading, and on the other hand, the use of two offset scales enables double readings to be used for reading control.

Digital levels do not use analog numbers that are written on the staff to determine the height reading. The measured value is generated by digital signal processing. The leveling staffs have to be adjusted accordingly. They are also equipped with an invar tape on which a manufacturer-specific binary code is applied (see barcode ). The reading is now made by comparing the staff section visible through the telescope with an image of the staff stored inside the device.

Errors and elimination

Defective circular level

A freely oscillating plumb bob is used to check the circular level on the leveling staff . This enables the staff to be positioned exactly vertically. If the bubble of the circular level does not swing in the middle, it can be precisely aligned using the adjusting screws.

Zero point error

When attaching the steel base or after frequent use of the leveling staff, it can happen that the lower edge of the staff no longer corresponds exactly to the zero point of the staff division. If only one staff is used in the course of a leveling, the constant error is eliminated by calculating the difference between the foresight and foresight. If you work with two staffs, this deviation can be eliminated by setting up an even number of instruments. If this is not possible, the zero point error must be determined and attached to the measurements. For this purpose, several staff arrangements are used that are visible from an instrument standpoint. Now each of the two laths must be placed one after the other on all lath bases and the heights can be read off using a leveled level . The zero point error can be determined from the differences between the corresponding readings on both staffs.

Contact surface error

Similar to the zero point error, it can happen that the contact surface is not even or not at right angles to the lath division. To check this, the staff is placed on 7 points that are distributed over the contact area. Please note that the middle must be included. The differences between the staff reading and the central position now indicate an unevenness of the steel base. When leveling , it is important to ensure that the lath is always placed in the middle of the contact surface on the lath base.

Slat division

The aim of checking the staff division is to check the internal division accuracy and the absolute length of the staff meter. Due to inaccuracies in the production of the lath, it can happen that the vertical division deviates from the cm intervals and this also increases linearly with the lath division. These systematic deviations only play a role with precise leveling of the highest accuracy and large height differences. The study of the staff division is carried out with a benchmark or on a comparator track with an interferometer .

Further error influences

Further inaccuracies when working with a leveling staff are caused by bending of the staff, inadequate fasteners and hinges on folding panels and loose foot fittings. However, these can only be avoided by careful handling and storage of the staff.

equipment

The staff shoe guarantees that the leveling staff is always placed on the frog with the same point on the contact surface . This prevents contact surface errors from having a negative effect on the measurements.

The frog is an essential accessory when working with leveling staffs. It "marks" a fixed point and ensures within the geometric leveling that the same point is held up when the staff is turned.

In the case of precision leveling and difficult wind conditions, handrails can be used to increase stability. They have the effect of greatly reducing the fluctuation of the staff and therefore increase the accuracy.

Probably the most important aid, which is always part of the leveling staff and is usually permanently attached, is the circular level . It enables the staff to be set up vertically and has a decisive influence on the accuracy and success of the geometric leveling.

literature

  • Fritz Deumlich , Rudolf Staiger: Instrument science of measurement technology. 9th edition. Wichmann, Heidelberg 2002, ISBN 3-87907-305-8 .
  • Heribert Kahmen: Applied Geodesy Surveying. Walter de Gruyter, 20th edition. Berlin 2006, ISBN 3-11-018464-8 .
  • Volker Matthews: surveying. Part 1. 28th edition. BG Teubner, Stuttgart 1996, ISBN 3-519-15252-5 .