*Question E6F05:
Which of the following describes an optical shaft encoder?*  

*Correct Answer is  A: A device that detects rotation by interrupting a light source with a patterned wheel*  

### AI Response: (may contain errors)  

An optical shaft encoder is a device used to measure the position or rotation of a shaft. Let's break down the correct answer and why the other options are incorrect.

### Correct Answer: 
**A: A device that detects rotation by interrupting a light source with a patterned wheel.**

- **Explanation**: An optical shaft encoder typically consists of a light source (like an LED) and a photodetector. A patterned wheel (often called a code disk) rotates between them. As the wheel turns, it interrupts the light beam in a specific pattern, generating electrical pulses that correspond to the rotation. This allows for precise measurement of angular position or speed.

### Why the Other Choices are Incorrect:

- **B: A device that measures the strength of a beam of light using analog-to-digital conversion.**
  - **Explanation**: This describes a light sensor or photodetector that converts light intensity into a digital signal, not a shaft encoder. An optical shaft encoder focuses on detecting rotation, not measuring light strength.

- **C: An optical computing device in which light is coupled between devices by fiber optics.**
  - **Explanation**: This refers to optical communication systems using fiber optics to transmit data, not a device for measuring rotation. Optical shaft encoders do not involve fiber optics for their operation.

- **D: A device for generating RTTY signals by means of a rotating light source.**
  - **Explanation**: RTTY (Radio Teletype) signals are generated using modulation techniques, typically involving radio frequencies, not a rotating light source. This option does not relate to the function of an optical shaft encoder.

### Summary:
- An optical shaft encoder detects rotation through light interruption by a patterned wheel, making option A the correct choice.
- The other options describe unrelated technologies or functions.

This understanding will help you recognize the specific applications of optical devices in the context of the Extra Class exam.