The movable target is placed on measurement points which are solidly installed into the top of a dam or a similar structure. It is used to determine horizontal movements of the crest in relation to a vertical reference plane (alignment plane, see Fixed Target).
| Target pattern | Concentric circles or Websky Gap | |
| Forced centering | Setting cone | |
| Size | Target plate | 140 x 123 mm |
| total size | 1550 x 225 x 68 mm (incl. tubular support) | |
| Weight | Target with tubular support | 9.6 kg |
In order to determine horizontal changes of the reference points in the alignment line perpendicular to the reference plane, movable targets are placed on top of those reference points. The targets are attached to a support with forced centering mechanism to make sure that each measurement is highly precise and repeatable.
There are two different types of set-up with forced centering mechanism: the movable target on a tubular support and the movable target on a tribrach. Both targets have a horizontal travel of ± 50 mm. The graduation of the horizontal scale is 1 mm, the graduation of the vernier is 0.1 mm.
If the first type “movable target on tubular support” is used, the movable target is firmly attached to the top of a metal tube which is 1.4 meters long. The tube has a conical-shaped opening at the bottom which is used to attach it to a setting cone with forced
centering mechanism (> 0.1 mm).
If the second type „movable target on tribrach” is used, the movable target is attached to a tribrach with the forced centering mechanism called “Freiberg Ball”. The tribrach is then placed on a support plate which is firmly installed in a concrete pillar.
The movable target is always equipped with a viewfinder which helps targeting the alignment telescope and thus finding the perpendicular position in relation to the alignment plane.
Example of use
- monitoring of the deformation behavior of water dams
