Which of the following statements regarding an electronic theodolite fitted with a graduated circle encoded in an incremental system is INCORRECT? 

Explanation:

• Electronic theodolite limbs are covered with a nontransparent coating that has code gaps on it.They may have regular intervals (incremental solution) and irregular ones (barcode solution).
• The source of light (light-emitting diode) is formed into a narrow beam with a condenser lens and a mask that has a slit. A slit grid is set in front of the photodetector. At the moment the slit grid moves, sinusoidal modulation of light occurs at the photodetector input.
• The sensor has two slits shifted one relative to the other at a one-fourth period phase of the grid step.
• There are also two photodetectors.When the grid moves to one direction a sinusoidal signal at one of the photodiodes output advances the signal at the output of the other photodiode.
• The photodiodes are placed one above the other.

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Additional Information

Electronic Theodolite

• In an electronic theodolite with an incremental encoding system, one photodiode is typically fixed, while the other is mounted on the moving part of the instrument, often the telescope.
• The fixed photodiode serves as a reference, and as the telescope moves, the changing pattern of light detected by the moving photodiode helps determine the angular position.
• In electronic theodolites with incremental encoding systems, the graduated circle is typically made of glass.
• Instead, it is often a metallic or magnetic disk with coded graduations.
• The coding on the disk can be read by the photodiodes to determine the angular position.
• In theodolites, the graduated circle is usually fixed, and the telescope or the entire instrument rotates to measure angles.
• The encoding system allows the instrument to accurately determine the angle of rotation.