In known apparatuses of this type which serve for measuring the inclination and horizontal displacement of buildings such as dams and houses, a displacement in the building or of the building relative and transverse to the plumb wire is mechanically sensed by means of a measuring device having a probe attached to the plumb wire. The deflection of the probe is likewise mechanically transmitted to an angle converter which generates electrical signals corresponding to the deflection of the probe. These signals are further processed for displaying the displacement or for outputting an alarm.
These known plumb systems have, however, the disadvantage that only positional changes in one direction can be detected with one measuring device. If the positional changes are to be measured in two directions, that is, in one plane, then two measuring devices must be provided. The continuous mechanical contact between the probe and the plumb wire causes an interfering deflection of the latter, and moreover results in wear phenomena which can lead to incorrect measurements. In order to avoid these, frequent checks and a correspondingly expensive maintenance are necessary.
Inclinometers for determining the inclination of objects are known which have a non-contacting position measuring device. (See Patent Abstracts of Japan, Volume 10, No. 102 (P-448) (2159) 18 April 1986 and U.S. Pat. No. 4,627,172.) These known devices have a housing which is fastened to the object to be monitored. A light source (light-emitting diode) is arranged in the housing and a photoelectric receiver is arranged opposite to the light source. The light emitted by the light source is transmitted via a light guide to the receiver. The light guide forms part of a pendulum mounted at one end of the housing.
These known inclinometers differ in their construction from the present invention and are less suitable for detecting positional changes in large buildings such as dams.