Short Answer:

A passive speed sensor works without any external power supply. It generates a signal based on the movement of a magnetic or metallic object, typically using the principle of electromagnetic induction. These sensors are simple, reliable, and mostly used for high-speed applications.

An active speed sensor, on the other hand, needs an external power source to operate. It includes internal electronics to amplify or process the signal, which allows it to work well even at low speeds. Active sensors are more accurate and offer better performance in varying conditions.

Detailed Explanation:

Difference between passive and active speed sensor

Speed sensors are used to measure the rotational speed of shafts, wheels, or other moving parts in electrical and mechanical systems. They help in controlling and monitoring the performance of vehicles, motors, machines, and automation systems. Based on how they work and whether they require power to operate, speed sensors are classified into passive and active types.

Understanding the difference between them is important for selecting the right sensor for the specific speed range, accuracy, and environmental conditions.

Passive Speed Sensor:

Definition:
A passive speed sensor does not require any external electrical power to operate. It works based on the principle of electromagnetic induction.

Working Principle:

• A magnetic pickup coil is placed near a rotating gear or toothed wheel.
• As the metallic teeth pass by the coil, they disturb the magnetic field.
• This change in magnetic field induces a small voltage (AC signal) in the coil.
• The frequency of this voltage corresponds to the speed of rotation.

Characteristics:

• Generates signal only when the target is moving.
• Does not work well at low speeds (because induced voltage is too weak).
• Simple, robust, and suitable for high-speed applications.
• Commonly used in engine crankshaft or gearbox speed detection.

Active Speed Sensor:

Definition:
An active speed sensor requires an external power supply to function. It contains electronic components such as amplifiers, signal conditioners, and sometimes microprocessors.

Working Principle:

• Uses technologies like Hall effect, optical, or magneto-resistive sensing.
• The sensor continuously monitors the presence and movement of the target object.
• Generates a digital or amplified analog signal even at zero or low speed.

Characteristics:

• Provides accurate output even at low speeds or during startup.
• Works in various environmental conditions, including dirt or moisture.
• More complex and expensive compared to passive sensors.
• Used in ABS systems, speedometers, and industrial automation.

Key Differences:

Feature	Passive Sensor	Active Sensor
Power Requirement	No external power	Requires power supply
Speed Range	Best for high speeds	Works well at low and high speeds
Output Signal	Low-level AC signal	Amplified digital/analog signal
Complexity	Simple design	More complex electronics
Accuracy	Lower at low speeds	High accuracy at all speeds
Cost	Cheaper	More expensive

Conclusion:

The main difference between a passive and active speed sensor is that passive sensors generate signals without power and are ideal for high-speed measurements, while active sensors need power but provide accurate results even at low speeds. Choosing the right type depends on the application requirements like speed range, accuracy, environment, and system design. Both have their own advantages in specific use cases.