A basic optical speed sensor, also known as a tachometer or RPM (revolutions per minute) sensor, is a device that measures the rotational speed of an object using optical principles. It works by detecting interruptions in a light beam caused by the object's rotating parts. Here's how it typically operates:
Emitter and Detector Setup: The optical speed sensor consists of two main components: an emitter and a detector. The emitter emits a focused beam of light towards the rotating object, and the detector is positioned on the opposite side of the object to receive the light after it passes through or reflects off the rotating parts.
Interrupted Light Beam: As the object starts to rotate, the parts on the object's surface pass through the light beam's path. Each time a part passes through the beam, it interrupts the light, causing the detector to momentarily detect a decrease in the amount of light reaching it.
Pulse Generation: The interruptions in the light beam create a series of pulses in the detector's output signal. The frequency of these pulses corresponds to the speed of the object's rotation. The faster the object rotates, the more interruptions occur in a given time frame, resulting in a higher frequency of pulses.
Signal Processing: The output signal from the detector is typically a square wave signal with varying frequency. To measure the speed accurately, this signal is sent to a signal processing circuit. This circuit may include components like counters, timers, and microcontrollers to convert the pulse frequency into a speed value in RPM or other units.
Calibration: Before using the optical speed sensor, it's important to calibrate it to ensure accurate measurements. Calibration involves determining the relationship between the pulse frequency and the actual rotational speed of the object. This might involve using a known reference speed or comparing the sensor's readings to a different type of speed measurement device.
Display or Output: Once the signal processing is complete, the calculated speed value can be displayed on a digital screen, sent to a computer or other devices for further analysis, or used to control other systems based on the measured speed.
Optical speed sensors are commonly used in various applications where monitoring rotational speed is important, such as in automotive engines, industrial machinery, conveyor systems, and more. They offer a non-contact method of measuring speed and are often chosen for their simplicity, reliability, and cost-effectiveness.