Cathetometer

A cathetometer is an optical apparatus for observing and measuring small changes in position of an object. It comprises a telescope, which is adjustable by means of screw bolts in the height and width. The complete structure is suitably mounted on a tripod to prevent tipping of the cathetometer. You can check whether the device is exactly horizontal on a dragonfly. Based on tenth of a millimeter scale, a positional change can be read.

Principle

The cathetometer performs an measurement, by determining the position of a point in two directions. The telescope is used here for observation of the point, the spindle drives are used for tracking of the telescope. Find the tracking place along a plane parallel to object motion axis, one can directly read off on the scale of tracking the position change. A shift to the cathetometer or away from it is not measurable.

Measurement

To measure a change in length with a cathetometer, one is this (often less than one meter ) in front of the object to be measured at an appropriate distance so that one the subject looks sharp through the lens. With a crosshair can be a certain point, eg, aim at the meniscus of a liquid column as a reference point. Targeting with this context means that one brings crosshair and reference point exactly at an angle of 0 ° to the horizontal in the lens to cover.

Now Before carrying out the change in length and measures, taking the values ​​for height or width as reference values ​​. After changing one aiming at the reference point again by driving the telescope with the spindle bolts up or down, recorded the height and width of the point and obtained from the difference to the reference values ​​, the absolute change in length.