What is an Automatic Level?

Published: 05th February 2011
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The automatic level is one of technology's more recent versions of the construction level. How is the automatic level different from earlier versions of construction levels such as the wye level and dumpy level? In order to understand what an automatic level is, we must first know a little about construction levels in general.

A construction level can be compared to a carpenter's level. The carpenter's level is used to determine if two points a few inches apart are level. Like the carpenter's level the construction level incorporates the spirit level, which is the little slightly curved glass vial filled with a colored spirit. In this case the spirit is alcohol with a bubble floating in it. But in order to transfer a level line a distance to another point, the construction level was developed with the spirit level attached to a telescope. The telescope is mounted on a vertical axis, about which it can swing horizontally and is leveled by four leveling screws. All of this makes up the instrument which is mounted on a tripod to stabilize it and to bring it up to the operator's eye level.

Examples of earlier versions of the construction level that utilized the spirit level are the wye level, also written "Y level"; the dumpy level; and the tilting dumpy level. The wye level has the spirit level attached to the telescope. The telescope rests on a horizontal bar that is rigidly attached to the vertical axis and leveled by three to four leveling screws. The wye level is unique in that the telescope can be unclamped and removed from the horizontal bar, turned end for end, and replaced. This is done when testing the bubble for adjustment. The wye level is generally no longer available as a new instrument.

The dumpy level is essentially constructed the same as the wye level except that the spirit level and telescope are rigidly attached to the cross bar and vertical axis making it all one piece. The advantage to the dumpy level over the wye level is that it can withstand rougher usage and still maintain its accuracy. The only real benefit the wye level has over the dumpy level is that the adjustment of line of sight can be a little more easily tested. The dumpy level is still in common use.

When operating the wye or dumpy level, the observer must constantly check the spirit level and adjust the leveling screws in order for the instrument to be truly level at the instant of observation. The tilting dumpy level has features to reduce the random error inherent to both the wye and dumpy level.

The tilting dumpy level is brought to approximate level with a bullís eye spirit level. The observer can then bring the instrument to true level by turning a tilting knob. He or she views the more sensitive main leveling bubble through either an eye piece adjacent to the telescope or within the field of view of the telescope itself. The observer sees the bubble as two half images of opposite ends of the same bubble that are separated longitudinally. This is called the "coincidence bubble." The viewing of the coincidence bubble is made possible by a special arrangement of prisms. The observer tilts the telescope with the tilting knob until the two half images correspond thus indicating the bubble is centered and the telescope is level.

Now we come to the automatic level. The automatic level is said to be self-leveling. When the automatic level is brought to near level position with a spirit level in the form of a vial or bull's eye level, then the leveling is completed by means of a prism carried on a pendulum inside the instrument. The pendulum that carries the prism is made-up of two pairs of wires. Light enters the large lens called the objective lens and is reflected through the prism to the eyepiece end of the telescope. The prism and the pendulum is so designed that only the horizontal, level rays of light are reflected through the cross hairs to the optical center of the objective lens. As a result even though the barrel of the instrument is only near level, the image viewed through the eye piece is horizontal and level.

The self-leveling feature makes the automatic level superior to the previous versions of the construction level by making it possible to set the instrument up more rapidly and by eliminating random errors that are created by maintaining a centered spirit level bubble.

Matt Reinhart is the author and a registered civil engineer. Visit Laser Levels USA to see a great selection of automatic levels and dumpy levels. While you are there, be sure to look through our full line laser levels including rotary laser levels, line lasers, laser plumb bobs, laser distance measures, and laser level accessories. Visit today for some incredible deals!

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