Leveling device
The leveling (also leveling , leveling device ) is a measuring instrument measured by the differences in height and height horizons are prepared.
For this purpose, the level has a telescopic sight , the target axis of which is aligned perpendicular to the plumb line by means of a precise level or similar device - today mostly a pendulum compensator . The riflescope can be freely rotated around the vertical standing axis - usually with an endless fine movement. You can therefore look all around with a horizontal line of sight. Any two points that lie in this horizon have the same height .
Use in construction and land surveying
In civil engineering , the level is used to create horizontal surfaces, to determine height differences or to set up machines and structures. The level replaces the spirit level where its accuracy is no longer sufficient and where it would be too time-consuming to use. The usual accuracy is
- for construction level (for setting out on construction sites) 1–5 mm per km of double leveling,
- for technical leveling (alignment, canal, etc.) 0.5 to 1 mm per km.
In national surveying , the level is used as a precision instrument to determine height networks and height points by fine leveling. Despite the sometimes long measuring distances, careful, densely networked measurements corrected with theoretical height reductions can be used to achieve high accuracies, which are better than 0.1 mm / km if necessary (see also European network and geoid determination ).
The measuring activity with the level is called leveling . As a rule, the level is placed on a three-legged tripod and fixed to the tripod plate with a strong knurled screw ( heart screw ). Additional measuring equipment includes the leveling staff , which is set up vertically on the measuring point. The scale of the leveling staff is read off the crosshair through the telescopic sight of the leveling device. If the reticle of the level also has spacer threads in addition to the crosshairs, the distance to the leveling staff can be determined with their help; such devices are called leveling total stations .
Leveling devices are differentiated according to their construction (e.g. according to telescope mobility or leveling device) and according to the area of application (construction level, engineering level, fine level) and the associated measuring accuracy.
Devices in which the telescope is aligned vertically instead of horizontally are called optical plummets . They are used, among other things, to sink shafts in mining.
Measurement method
Height differences are measured with the level. For this purpose, the level is set up in the middle between two measuring points and leveled if possible. A leveling staff is set up vertically at each measuring point . A scale is attached to the leveling staff in such a way that the reading of the staff division in the leveling device gives the vertical distance of the point from the height horizon ( device horizon ) of the level. If measurements are taken at another point with the level set up unchanged, the difference between the two readings gives the difference in height between the two points.
Basically, the level should be set up at the same distance from the measuring points. With this “leveling from the center”, a target axis error remains ineffective and the curvature of the earth does not cause the error. You should also make sure that you always play the instrument on the same staff. This eliminates the slope of the horizon ( “Rote Hose” method ).
The measurement is divided into sections so that a height difference can be measured over a greater distance, over greater height differences or around obstacles. Each section consists of the measurement from the known point to the new point. The level is set up horizontally between the two, i.e. the target line is horizontal. The well-known point looking back , called the new point is foresight . The readings are subtracted, backsight minus foresight, to get the elevation gain.
When you arrive at the destination, the height differences of all sections are added to get the height difference between the starting point and the destination.
Typical construction of the leveling device
The telescope
The telescope needs a crosshair as an aiming aid as well as an adjustment in order to be able to focus on close objects. It used to be a Kepler telescope with an eyepiece extension. Due to the increasing play due to wear and tear, it was designed to be rotatable or convertible in order to be able to compensate for the resulting height error. Since the invention of the apochromats , these have been used exclusively because of their geometrically error-free mapping. An image reversal system (lenses) was omitted in order not to negotiate further sources of error. So the picture was reversed and reversed, but this was irrelevant for aiming at a measuring point or a measuring stick.
With the invention of the more precise and less susceptible internal focusing, it was possible to dispense with moving the telescope, and the devices became more compact.
Image reversal (with prisms) was only rarely built in; it was only used consistently with the introduction of automatic levels.
The graticule with the crosshairs still contains distance lines throughout to enable you to read the distance to the measuring stick.
Dragonfly level
The leveling of the target line is carried out with the help of a tube level that is firmly connected to the telescope.
North German level
With the north German level, the telescope carrier and the telescope are rigidly connected to one another. The three foot screws are used to bring in the tube level attached to the telescope (= leveling the instrument). If the error-free instrument is set up correctly, the sighting axis of the telescope describes a horizontal plane as it rotates. This device is therefore particularly suitable for surface leveling in flat terrain (North German level). Here, many terrain points can be read from one instrument position - without readjusting the level. This assumes that there is a right angle between the vertical axis and the vial axis and that the bubble of the tubular vial is brought in. Slight deviations of the sighting axis from the horizontal as a result of the influence of heat and the vibrations are practically of no significance here.
South German level
With the southern German level, the telescope carrier and telescope are not rigidly connected to one another. Rather, the telescope can be tilted slightly in the longitudinal direction by a vertically acting fine movement screw, the so-called tilt screw. First, the circular level attached to the telescope carrier is brought in with the foot screws . The vertical axis of rotation is thus approximately perpendicular. Before each reading on the leveling staff, the tubular level attached to the telescope is brought in sharply with the help of the tilt screw, i.e. the vertical axis does not have to be exactly perpendicular. This instrument developed by Sickler is particularly suitable for the precise recording of individual points, such as for fixed point leveling .
Self-leveling ("automatic") level
The self-leveling level has a compensator instead of the telescopic level (target line regulator for automatic leveling). This consists of opto-mechanical components that are inserted into the beam path of the telescope. These components automatically set the finish line horizontally within a small area. Because of the limited workspace of the compensators a Vorhorizontierung with is circular level required.
A pendulum prism is often used as a compensator for fine leveling, which, when suspended from bands in the level, deflects the line of sight against the incorrect leveling of the leveling device.
Digital level
The digital level, a self-leveling, self-reading and recording leveling instrument, is a combination of a compensator level and a digital camera. The target beam passes through the same beam path as with the compensator level, but is separated into infrared and visible light with a splitter cube. The infrared light goes into the CCD chip and the visible light reaches the viewer unhindered. The leveling staff is provided with a barcode (comparable to the price recognition at the supermarket checkout). The image of the barcode is compared with a stored image in the level. If they match, the saved value is output digitally, shown on the display and saved internally on a memory card for digital evaluation.
exam
To test leveling devices, there is the “from the middle” method, the “Näbauer” method, the “Kukkamäki” method and the “Förstner” method.
Web links
Individual evidence
- ↑ Neitzel, Petrovic: A generalized field method for checking leveling devices . (PDF)