Short Answer:

A magnetic pickup sensor measures rotational speed by detecting the movement of a rotating metallic object, usually a gear or toothed wheel. As the teeth pass by the sensor, they disturb the magnetic field created by the sensor, which induces a voltage signal in the coil inside it.

Each passing tooth creates one electrical pulse. By counting the number of pulses over a specific time, the sensor calculates the rotational speed in revolutions per minute (RPM). This method is simple, reliable, and commonly used in engines, motors, and turbines.

Detailed Explanation:

Magnetic pickup sensor rotational speed measurement

A magnetic pickup sensor, also called a variable reluctance sensor, is a non-contact sensor used to measure the rotational speed of metal objects. It operates based on electromagnetic induction, which is the generation of voltage when a magnetic field changes around a conductor.

This type of sensor is highly durable, needs no external power supply for basic operation, and can function in harsh environments such as high temperatures or oily machine surroundings.

Main Components:

1. Permanent Magnet – Creates a constant magnetic field.
2. Coil of Wire – Wrapped around the magnet; it senses voltage changes.
3. Sensing Face – Placed close to a rotating metallic object like a gear or shaft with teeth.

Working Principle:

1. Positioning:
   The magnetic pickup sensor is installed very close to a rotating part that has evenly spaced teeth or notches (like a gear wheel or flywheel). The sensor does not touch the moving part.
2. Magnetic Field Change:
   The sensor generates a static magnetic field. When a metal tooth comes near the sensing face, the metal interrupts or disturbs this magnetic field.
3. Induced Voltage:
   As each tooth passes, the magnetic field strength changes, and this change induces a voltage (AC signal) in the coil according to Faraday’s Law of Electromagnetic Induction.
4. Pulse Generation:
   Every passing tooth generates one voltage pulse. The output signal is a series of pulses, where each pulse represents one portion of a rotation.
5. Speed Calculation:
   The frequency (number of pulses per second) is measured. Using the number of gear teeth and pulse rate, the rotational speed in RPM is calculated using the formula:

RPM=(Pulse Frequency×60Number of Teeth)\text{RPM} = \left( \frac{\text{Pulse Frequency} \times 60}{\text{Number of Teeth}} \right)RPM=(Number of TeethPulse Frequency×60​)

For example, if there are 30 teeth and the sensor detects 300 pulses per second:

RPM=(300×6030)=600RPM\text{RPM} = \left( \frac{300 \times 60}{30} \right) = 600 RPMRPM=(30300×60​)=600RPM

Advantages:

• Non-contact sensing – no physical wear
• No external power required for basic sensing
• Rugged and reliable in harsh conditions
• Simple and low cost
• Works well with metal targets

Limitations:

• Only detects ferromagnetic materials (like steel or iron)
• Signal may weaken at very low speeds
• Requires a consistent gear tooth pattern
• Susceptible to electromagnetic noise

Applications:

• Automotive crankshaft and camshaft speed sensing
• Industrial motor speed control
• Gas turbines and generators
• Gearbox speed monitoring
• Engine diagnostics and testing

Conclusion:

A magnetic pickup sensor measures rotational speed by detecting voltage pulses generated as metallic teeth pass through its magnetic field. These pulses are counted and used to calculate RPM accurately. This method is widely used in mechanical and electrical systems due to its durability, simplicity, and ability to operate without direct contact.