Describe the operation of a rotational speed sensor.

A rotational speed sensor, also known as a tachometer or rotational speed transducer, measures the rotational speed (angular velocity) of a rotating object, such as a shaft, motor, or engine. There are various types of rotational speed sensors, each operating on different principles. Here’s an overview of the operation of a rotational speed sensor using some common techniques:

Magnetic Induction (Magnetic Pickup):

In magnetic induction-based rotational speed sensors, a magnetic pickup generates an electrical signal proportional to the speed of a rotating gear or toothed wheel.
The sensor consists of a coil wound around a magnet, and as the gear or wheel rotates, the magnetic field passing through the coil changes, inducing a voltage or current in the coil.
The frequency of the induced signal is directly proportional to the rotational speed of the gear or wheel. Signal conditioning circuitry may be used to amplify and process the signal.
Hall Effect Sensor:

Hall effect sensors detect changes in magnetic field strength using the Hall effect, which is the creation of a voltage difference (Hall voltage) across a conductor when subjected to a magnetic field perpendicular to the current flow.
In a rotational speed sensor application, a magnetized target or gear passes by a Hall effect sensor, causing a change in magnetic field strength.
The Hall effect sensor detects this change and generates a corresponding electrical signal, the frequency of which is proportional to the rotational speed of the target.
Optical Sensor:

Optical sensors use light-based techniques to detect rotational speed. These sensors typically consist of a light source and a photodetector (e.g., photodiode or phototransistor) positioned opposite each other across a rotating shaft.
As the shaft rotates, interruptions or changes in the light beam caused by slots or reflective surfaces on the shaft are detected by the photodetector, generating electrical pulses.
The frequency of these pulses is proportional to the rotational speed of the shaft.
Inductive Sensor:

Inductive sensors detect changes in inductance caused by the movement of a metal target. As the target rotates, it alters the inductance of a coil in the sensor.
The change in inductance induces a voltage or current in the coil, which is converted into an electrical signal proportional to the rotational speed of the target.
Ultrasonic Sensor:

Ultrasonic sensors measure the time it takes for ultrasonic waves to reflect off rotating objects.
By emitting ultrasonic pulses and measuring the time delay between transmission and reception of the reflected signal, the sensor can determine the rotational speed of the object.