Question

Optical sensors used for the displacement measurement works on the principle:

• A. Intensity of light increases with distance
• B. Intensity of light decreases with distance
• C. Intensity of light remains constant with distance
• D. Intensity of light increases with time

Hint:

Think of the inverse-square law for light propagation: as distance from a source increases, the intensity of light falling on a fixed aperture decreases.
This simple geometric property is the basis of reflective optical displacement transducers.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks about the operating principle of intensity-modulated optical sensors used for measuring physical displacement.

Step 2: Detailed Explanation:

• Intensity-modulated fiber optic displacement sensors typically consist of a light-transmitting fiber, a reflective target surface, and a light-receiving fiber.

• The transmitting fiber directs light onto the target surface, and the reflected light is captured by the receiving fiber and sent to a photodetector.

• As the distance (displacement) between the sensor probe and the target surface increases, the reflected light beam diverges over a larger area.

• Because of this beam divergence, the density of light returning to the receiving fiber drops, meaning the detected intensity of light decreases as distance increases.

• By calibrating this decrease in light intensity against the distance, the sensor can accurately measure the displacement of the target.

Step 3: Final Answer:
Optical sensors used for displacement measurement work on the principle that the intensity of light decreases with distance.