Sensors can be classified in many ways, but the two main types of sensors are active sensors and passive sensors. These two types are categorized based on how they detect signals and whether they require an external power source to operate.
An active sensor is a type of sensor that needs an external power supply to work. It sends out its own signal or energy into the environment and then measures how that energy is changed by the target object. The sensor uses this information to detect presence, distance, or other parameters. A good example is a photoelectric sensor, which emits a beam of light and detects when something interrupts or reflects that beam. Another example is an ultrasonic sensor, which sends sound waves and measures the time they take to return after hitting an object. Active sensors are widely used in automation systems because they provide fast, accurate detection even over longer distances.
A passive sensor, on the other hand, does not generate any energy of its own. Instead, it detects natural changes or signals coming from the environment or the object being measured. These sensors only receive information — they don’t emit anything. A simple example is a temperature sensor like a thermocouple or RTD, which senses the heat energy produced by an object. Another example is a proximity sensor, which detects the presence of an object by sensing variations in magnetic or electrical fields. Passive sensors are very reliable and are often used where continuous monitoring of a physical property like heat, light, or pressure is needed.
Both types of sensors are essential in automation and control systems. Active sensors are ideal for precise distance measurement, object detection, and motion sensing, while passive sensors are preferred for monitoring natural parameters like temperature, pressure, and vibration.
In industries using advanced sensing technology such as Omron sensors, both active and passive types play a crucial role in improving accuracy, machine safety, and process efficiency across manufacturing, packaging, and robotics applications.