Light pointer
A light pointer enables a measuring device to display the smallest changes in measured values that would not be easily represented with a normal mechanical pointer. Instead of a pointer, a mirror is attached to the shaft that reflects a bundled light or laser beam .
Due to the extremely large pointer length and the doubling of the deflection due to the mirror law ( angle of incidence = angle of reflection), a large deflection is achieved even with small rotations of the pointer shaft on a scale that is far away :
While - as shown in the picture on the right - the deflection of 1 degree is hardly recognizable with the conventional pointer, a clearly visible display is already achieved on the further away scale with the light pointer. The resolution of the measuring device increases to the same extent as the distance between the mirror and the scale.
An additional advantage of the light pointer is its negligible mass (only shaft and mirror with mass concentration near the axis of rotation ). While rapid display changes are not possible with a long mechanical pointer due to its considerable inertia , the low inertia of the light pointer also allows the display of fast processes such as changing the amplitude of sound waves (scanning a record with the needle).
Another advantage of this display principle is the principle of avoiding a parallax error in contrast to mechanical pointers.
Light pointers are u. a. used in mirror galvanometers .
In galvanometer scanners, moving mirrors deflect a laser beam in order to write characters or figures (see laser show , laser scanning ).
A similar principle can be found in laser projectors and barcode scanners , here continuously rotating prismatically arranged mirrors ensure that the laser beam sweeps over a line or an area line by line.