| The right prism For maximum accuracy and maximum range. Various aspects define the achievable measurement precision and distance range of prisms. The most significant of these are Reflective Coating, the Angular Beam Deviation and Anti-reflex Coating. Light-weight, passive reflectors for use with robotic Total Stations. For efficient operation without the need for directing the reflector toward the instrument, a 360° prism is required. This type of reflector consists of six corner-cube prisms joined together. The arrangement allows the measuring beam to reflect directly back to its source from any position on the prism set. The even distribution of the prisms provides similar offset and accuracy readings from any side. Reflective Coating Leica Geosystems prisms have a copper coating on the reflection surfaces. Copper offers a very high reflectance of infrared beams. Being robust and resistant to corrosion, the coating has a long useable life. Without a reflective coating, the distance measuring, ATR and PowerSearch range reduces by over 30%. In addition, incorrect measurements can result when moisture forms droplets on the reflecting surface. Angular Beam Deviation The precision to which the prism glass is cut is measured in terms of the Angular Beam Deviation. This is the angular difference between the entering and exiting measurement beam. The higher this deviation, the weaker the returned signal strength to the EDM and hence the shorter the measuring range. Anti-reflex Coating The front surface of most Leica Geosystems prisms has an anti-reflection coating. Without this, the front face of a prism reflects a part of the EDM signal. At close ranges, this causes incorrect distance measurements. The coating is optimised for the frequency of the Leica Geosystems distance measuring signal. Therefore other brands of coated prisms still partially reflect and can cause incorrect measurements. |