A basic optical speed sensor, also known as an optical encoder or tachometer, is a device used to measure the rotational speed of a moving object, typically a motor or shaft. It works based on the principles of light sensing and interruption. Here's a description of its operation:
Light Source: The speed sensor consists of a light source, usually an infrared LED (Light Emitting Diode). The LED emits a focused beam of light onto the target object, such as a rotating disc or a slotted wheel.
Sensing Element: Opposite to the light source, there is a light-sensitive element like a photodiode or a phototransistor. This element is placed in such a way that it receives the light beam that passes through or reflects off the rotating object.
Slotted Wheel or Encoder Disc: The rotating object is often equipped with a slotted wheel or an encoder disc. This wheel has evenly spaced slots or transparent areas around its circumference.
Detection of Slots or Interruption: As the object rotates, the slots on the wheel come in between the light source and the sensing element. When a slot passes between them, it interrupts the light beam, causing the photodiode or phototransistor to register a change in light intensity.
Electrical Signal Generation: The photodiode or phototransistor converts the detected light intensity changes into electrical signals. These signals are typically in the form of digital pulses.
Counting and Speed Calculation: The electrical pulses generated by the sensor are fed into a counting circuit or microcontroller. The counting circuit keeps track of the number of pulses received over a specific time duration. The frequency of the pulses directly corresponds to the speed at which the slotted wheel or encoder disc is rotating.
Speed Output: The sensor processes the counted pulses and calculates the rotational speed of the object. The speed information can be displayed on a digital screen, sent to a control system, or used for various applications, such as controlling the speed of a motor or providing feedback to a speed control mechanism.
In summary, a basic optical speed sensor works by emitting a light beam onto a rotating slotted wheel or encoder disc and detecting interruptions in the light beam as the slots pass through. The interruptions are converted into electrical pulses, and the frequency of these pulses is used to calculate the rotational speed of the object. Optical speed sensors are commonly used in various applications, including industrial machinery, robotics, automotive systems, and more.