Level (optical instrument): Difference between revisions
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[[Image:Us land survey officer.jpg|thumb|Automatic level in use on a construction site]] |
[[Image:Us land survey officer.jpg|thumb|Automatic level in use on a construction site]] |
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==Invention== |
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In 1832, [[English people|English]] [[civil engineer]] [[William Gravatt]], who had worked with [[Marc Isambard Brunel]] and his son [[Isambard Kingdom Brunel|Isambard]] on the [[Thames Tunnel]], was commissioned by Mr. H.R. Palmer to examin a scheme for the [[South Eastern Railway, UK|South Eastern Railway's]] route from London to [[Dover]]. Forced to use the then conventional [[Y level]], during the works Gravatt devised the more transportable and easier to use dumpy level.<ref>{{cite book|title=Surveying|author=Saikia, Et Al.|publisher=PHI Learning|date=30 Oct 2010|ISBN=8120339851}}</ref><ref>{{cite web|url=http://www.craig-telescope.co.uk/life_gravatt.html|title=William Gravatt|publisher=craig-telescope.co.uk|accessdate=2012=05-31}}</ref> |
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==Operation== |
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The level instrument is set up on a [[Tripod (surveying)|tripod]] and, depending on the type, either roughly or accurately set to a leveled condition using footscrews (levelling screws). The operator looks through the eyepiece of the telescope while an assistant holds a tape measure or graduated staff vertical at the point under measurement. The instrument and staff are used to gather and/or transfer elevations (levels) during site surveys or building construction. Measurement generally starts from a [[Benchmark (surveying)|benchmark]] with known height determined by a previous survey, or an arbitrary point with an assumed height. |
The level instrument is set up on a [[Tripod (surveying)|tripod]] and, depending on the type, either roughly or accurately set to a leveled condition using footscrews (levelling screws). The operator looks through the eyepiece of the telescope while an assistant holds a tape measure or graduated staff vertical at the point under measurement. The instrument and staff are used to gather and/or transfer elevations (levels) during site surveys or building construction. Measurement generally starts from a [[Benchmark (surveying)|benchmark]] with known height determined by a previous survey, or an arbitrary point with an assumed height. |
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==Variants== |
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Some dumpy levels will have a bubble level ensuring an accurate level. |
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| ⚫ | A '''dumpy level''' is an older-style instrument that requires skilled use to set accurately. The instrument requires to be set level (see [[spirit level]]) in each quadrant, to ensure it is accurate through a full 360° traverse. Some dumpy levels will have a bubble level ensuring an accurate level. |
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A variation on the dumpy and one that was often used by surveyors, where greater accuracy and error checking was required, is a '''tilting level'''. This instrument allows the telescope to be effectively flipped through 180°, without rotating the head. The telescope is hinged to one side of the instrument's axis; flipping it involves lifting to the other side of the central axis (thereby inverting the telescope). This action effectively cancels out any errors introduced by poor setup procedure or errors in the instrument's adjustment. As an example, the identical effect can be had with a standard builder's level by rotating it through 180° and comparing the difference between [[spirit level]] bubble positions. |
A variation on the dumpy and one that was often used by surveyors, where greater accuracy and error checking was required, is a '''tilting level'''. This instrument allows the telescope to be effectively flipped through 180°, without rotating the head. The telescope is hinged to one side of the instrument's axis; flipping it involves lifting to the other side of the central axis (thereby inverting the telescope). This action effectively cancels out any errors introduced by poor setup procedure or errors in the instrument's adjustment. As an example, the identical effect can be had with a standard builder's level by rotating it through 180° and comparing the difference between [[spirit level]] bubble positions. |
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[[File:Automatic Level.svg|thumb|250px|An automatic level uses a swinging prism to compensate for small inclination deviations.]] |
[[File:Automatic Level.svg|thumb|250px|An automatic level uses a swinging prism to compensate for small inclination deviations.]] |
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An '''automatic level''', '''self-levelling level''' or builder's auto level, includes an internal compensator mechanism (a swinging [[prism (optics)|prism]]) that, when set close to level, automatically removes any remaining variation from level. This reduces the need to set the instrument truly level, as with a dumpy or tilting level. Self-levelling instruments are the preferred instrument on building sites, construction and surveying due to ease of use and rapid setup time. |
An '''automatic level''', '''self-levelling level''' or builder's auto level, includes an internal compensator mechanism (a swinging [[prism (optics)|prism]]) that, when set close to level, automatically removes any remaining variation from level. This reduces the need to set the instrument truly level, as with a dumpy or tilting level. Self-levelling instruments are the preferred instrument on building sites, construction and surveying due to ease of use and rapid setup time. |
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A '''digital electronic level''' is also set level on a tripod and reads a bar-coded staff using electronic laser methods. The height of the staff where the level beam crosses the staff is shown on a digital display. This type of level removes interpolation of graduation by a person, thus removing a source of error and increasing accuracy.During night time dumpy level is used along with auto cross laser for accurate scale readings. |
A '''digital electronic level''' is also set level on a tripod and reads a bar-coded staff using electronic laser methods. The height of the staff where the level beam crosses the staff is shown on a digital display. This type of level removes interpolation of graduation by a person, thus removing a source of error and increasing accuracy.During night time dumpy level is used along with auto cross laser for accurate scale readings. |
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==See also== |
==See also== |
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* [[Theodolite]] |
* [[Theodolite]] |
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* [[Total station]] |
* [[Total station]] |
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==References== |
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{{reflist}} |
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==External links== |
==External links== |
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Revision as of 00:17, 1 June 2012
A dumpy level, builder's auto level, leveling instrument, or automatic level is an optical instrument used to establish or check points in the same horizontal plane. It is used in surveying and building to transfer, measure, or set horizontal levels.
Invention
In 1832, English civil engineer William Gravatt, who had worked with Marc Isambard Brunel and his son Isambard on the Thames Tunnel, was commissioned by Mr. H.R. Palmer to examin a scheme for the South Eastern Railway's route from London to Dover. Forced to use the then conventional Y level, during the works Gravatt devised the more transportable and easier to use dumpy level.[1][2]
Operation
The level instrument is set up on a tripod and, depending on the type, either roughly or accurately set to a leveled condition using footscrews (levelling screws). The operator looks through the eyepiece of the telescope while an assistant holds a tape measure or graduated staff vertical at the point under measurement. The instrument and staff are used to gather and/or transfer elevations (levels) during site surveys or building construction. Measurement generally starts from a benchmark with known height determined by a previous survey, or an arbitrary point with an assumed height.
Variants
The term dumpy level endures despite the evolution in design. A dumpy level is an older-style instrument that requires skilled use to set accurately. The instrument requires to be set level (see spirit level) in each quadrant, to ensure it is accurate through a full 360° traverse. Some dumpy levels will have a bubble level ensuring an accurate level.
A variation on the dumpy and one that was often used by surveyors, where greater accuracy and error checking was required, is a tilting level. This instrument allows the telescope to be effectively flipped through 180°, without rotating the head. The telescope is hinged to one side of the instrument's axis; flipping it involves lifting to the other side of the central axis (thereby inverting the telescope). This action effectively cancels out any errors introduced by poor setup procedure or errors in the instrument's adjustment. As an example, the identical effect can be had with a standard builder's level by rotating it through 180° and comparing the difference between spirit level bubble positions.
An automatic level, self-levelling level or builder's auto level, includes an internal compensator mechanism (a swinging prism) that, when set close to level, automatically removes any remaining variation from level. This reduces the need to set the instrument truly level, as with a dumpy or tilting level. Self-levelling instruments are the preferred instrument on building sites, construction and surveying due to ease of use and rapid setup time.
A digital electronic level is also set level on a tripod and reads a bar-coded staff using electronic laser methods. The height of the staff where the level beam crosses the staff is shown on a digital display. This type of level removes interpolation of graduation by a person, thus removing a source of error and increasing accuracy.During night time dumpy level is used along with auto cross laser for accurate scale readings.
See also
References
- ^ Saikia; et al. (30 Oct 2010). Surveying. PHI Learning. ISBN 8120339851.
{{cite book}}: Explicit use of et al. in:|author=(help) - ^ "William Gravatt". craig-telescope.co.uk. Retrieved 2012=05-31.
{{cite web}}: Check date values in:|accessdate=(help)
External links
- Dumpy level, from a surveying instrument collection.
- Checking a level