Answer

1. What is Proximity Sensor?

Sensor that detects presence of nearby object without physical contact via field/radiation. Range typically 0–50 cm (IR, ultrasonic, inductive). Output binary (present/absent) or analog (distance).

2. How It Works

Object entering sensing field disturbs field → detector measures change → threshold → output.

• Inductive: Oscillator coil → eddy currents in metal → amplitude drop → comparator.
• Capacitive: Electrode capacitance $C=\epsilon A/d$ → object changes $\epsilon$ → frequency shift.
• IR: IR LED emits, photodiode measures reflected intensity $I\propto1/d^2$.
• Ultrasonic: Emit chirp, measure time-of-flight $d=c\cdot TOF/2$.

3. Types

Type	Target	Principle	Range
Inductive	Metal	Eddy current	1–10 mm
Capacitive	Any (dielectric)	Capacitance	0–20 mm
IR	Reflective	IR reflection	2–30 cm
Ultrasonic	Any	TOF	2cm–4m
** Hall/Magnetic**	Magnet	Hall effect	mm

4. Advantages

• Non-contact → no wear.
• Fast response (ms).
• Reliable in dirty environments (vs vision).
• Simple interface (digital/analog).

5. Disadvantages

• Limited range.
• Material dependence (inductive only metal, IR affected by color).
• Ambient interference (light, sound, temperature).
• Not precise distance (except ultrasonic).

6. Applications

• Robot obstacle avoidance, end-effector positioning.
• Conveyor part detection, mobile robot navigation.
• Security systems, touchless switches.
• Assembly line counting.

Final Answer

Proximity = non-contact presence detector via electromagnetic/acoustic field disturbance; types inductive/capacitive/IR/ultrasonic; used for avoidance and detection with non-contact advantage but limited range/material dependence.