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.
For more accurate work the "dumpy level" is very useful. It consists of a telescope mounted on a tripod stand, and can be moved about in all directions. Attached to the telescope is a delicate spirit level and often a ring compass. The telescope is adjusted properly when the bubble in the spirit level is exactly in the centre when the telescope is turned backwards and forwards, and when the cross hairs on the lens are distinctly seen. The attached level is then said to be parallel to the "line of collimation" of the telescope. In using the Dumpy level the tripod is fixed firmly on the ground and the operator looks through the telescope on to the levelling rod placed on a certain spot. The levelling rod varies in height up to 3m and 5m., and has three pieces which may be drawn out if necessary.
In simple levelling the dumpy level remains in one position, from which all readings are taken. The first reading is called the "back sight" and the last the "fore sight". The difference in the readings of the back sight and fore sight is equal to the difference of level of the two points. Thus, if the back sight is read as 9.50 ft. and the fore sight at 13.75 ft. there is a fall from the back-sight point to the fore sight of 4.25 ft. Where, however, the ground is of an irregular nature it may be necessary to take several levels.
How to use a dumpy level:
Its really simple, all you need is Tripod and a Staff, the staffs are also known as English staffs, E meter staff, E Staff or just simply a graduated rule.
Set the level on top of the tripod, make accurate with the thumbscrews located at the base, this will micro adjust the case by a few mm each way - do this until the bubble is in the centre of the marker.
Once your level is set correctly, have your team mate stand with the staff vertical and resting at the start of the foundation trench for e.g. and you simply look through the dumpy level and read the markings on the staff as he moves away from you in distance's. From there you can easily see if you need to dig out more or backfill.
Other uses for your dumpy level and staff can include: Determining the height of a particular point, Determining differences in height between points, Determining the contours of a land profile, Providing data for road cross-sections, Providing data to calculate volumes for earthworks, Setting out level surfaces for construction and Setting out inclined surfaces for construction.
To get accurate results these basic guidelines should be followed. Clear lines of sight are needed between known and unknown points. Height precision is dependant upon the accuracy of the instrument used and the distance away your staff is.
What is difference between an auto level and a dumpy level?
A Dumpy Level is an older style level that required 'user' skill to set accurately. Some will have a spirit level to set accurately. An automatic level includes an internal compensator mechanism, which when set automatically removes any variation. Auto levels are thus much easier to use and set up time is a lot quicker
What is the difference between a theodolite and a dumpy level?
In dumpy level we can check only horizontal angles whereas in theodolite we can check vertical angles also.
How to calibrate a dumpy level?
Purpose: To describe the instruction for the calibration of Dumpy Level to ensure that equipment
is maintained in fully serviceable condition, is safe to operate and meets environmental requirements.
The method described below is to be used on-site check prior to use as to the accuracy of the
Dumpy level between calibration checks.
This Work instruction shall be conducted at the commencement and completion of a contract.
1. Drive two pegs, "A" & "B", into the ground six metres or more apart
2. Set Dumpy up at "C"
3. Shoot a level at "A" and "B"
4. Relocate Dumpy to "D" and shoot a level at "A" and "B"
5. Record the appropriate result in the workbook.
(Levels shot at "D" should be within +/- 10mm of "C")
Why the instrument is named as dumpy level?
It is an old builders nickname that has stuck, despite the evolution in design. It is named so because of the shorter telescope it uses and also because in the original dumpy level the eye piece was an inverting lens such that it gave a shorter view for the same power of lens compared to wye level.