1. A gear with 60 teeth is fixed on the shaft. Each tooth is a repeating feature that the sensor can detect.
2. A sensor is mounted close to the teeth, usually 0.5 to 1.5 mm away. For an inductive pickup the passing steel changes the magnetic field. For a Hall sensor it changes the field around a small magnet. For an optical sensor it breaks a beam.
3. Each tooth produces one electrical pulse. The pulse is a voltage spike for a magnetic pickup, or a clean square wave for a Hall or optical sensor.
4. A counter or controller measures how many pulses arrive in a fixed time, or the time between two pulses.
5. It converts: RPM = pulses per second x 60 / teeth per revolution.

Suppose the controller counts 1,200 pulses in one second from the 60-tooth gear. That is 1,200 / 60 = 20 revolutions per second, or 1,200 RPM. If the shaft slows and only 300 pulses arrive, the answer becomes 300 RPM. Nothing in the sensor changed, only the pulse rate.

A zero-speed switch uses the same pulses in a simple way. If no pulse arrives for a set time, the shaft is considered stopped and an output trips. That is how a conveyor knows a belt has broken.

Each card below shows the sensor in use, what it is and how it works, and where you will find it.

SENSOR 1 OF 8

Inductive Speed Sensor (Magnetic Pickup)

An inductive speed sensor (magnetic pickup) has a coil wound around a magnet. When a metal gear tooth passes by, the magnetic field changes and a voltage pulse is generated in the coil. The pulse frequency is proportional to the speed. It needs no power supply and is very rugged, so it is used on engines and gearboxes.

USED IN

enginesgearboxes

SENSOR 2 OF 8

Hall-Effect Speed Sensor

A Hall-effect speed sensor detects the teeth of a gear or a magnetic ring using a Hall chip. Each tooth that passes causes a change in the magnetic field and gives a clean square-wave pulse. It can sense even very low speeds down to zero, so it is used for wheel speed in ABS systems.

USED IN

vehicle wheelsABS

SENSOR 3 OF 8

Optical Speed Sensor

An optical speed sensor uses a light beam and a slotted disc or a reflective mark on a rotating part. Each time the beam is cut or reflected, a pulse is produced. Counting these pulses per second gives the speed. It is accurate and low cost but needs a clean environment.

USED IN

office equipmentsmall motors

SENSOR 4 OF 8

Encoder-Based Speed Sensor

An encoder-based speed sensor uses the pulses of an encoder fitted on a shaft. The controller counts how many pulses arrive in a fixed time, or measures the time between pulses, and converts this to RPM. It gives accurate speed and also direction, so it is used in drives and conveyors.

USED IN

conveyorsdrives

SENSOR 5 OF 8

Tachometer Pickup

A tachometer pickup senses the rotation of a shaft, usually by detecting a mark, a gear tooth or a magnet on it, and gives a signal for each turn. A meter or controller then displays or uses the RPM. It is a simple way to check and monitor shaft speed.

USED IN

shaftsspindles

SENSOR 6 OF 8

Doppler Radar Speed Sensor

A Doppler radar speed sensor sends out radio waves toward a moving object or the ground. The reflected waves come back with a slightly different frequency, and the difference is proportional to speed. It measures speed without any contact or wheel, so it is used on tractors and vehicles.

USED IN

tractorsvehicles

SENSOR 7 OF 8

Tachogenerator

A tachogenerator is a small DC or AC generator fitted on a motor shaft. The faster the shaft turns, the higher the voltage it produces, so the output voltage is a direct measure of speed. It is simple and gives a smooth analogue signal, so it is used in DC drives and rolling mills.

USED IN

DC drivesrolling mills

SENSOR 8 OF 8

Zero-Speed Switch

A zero-speed switch checks whether a shaft or machine is moving or stopped. It senses rotation using a proximity or magnetic sensor and gives a signal when the speed falls below a set value. It is used for safety and protection on conveyors, elevators and crushers, to detect a stall or a belt break.

USED IN

conveyorselevatorscrushers