Have you ever wondered how in an automated production line or an industrial conveyor system, an object is detected or placed in a specific position? Or in a public washroom how water flows from a tap without touching it? This is where a special sensor known as the proximity sensor comes handy. By using a proximity sensor, nearby objects can be detected without physical contact.
In order to automate complex production systems, it becomes necessary to have components that can collect and transmit information about the production processes. Proximity sensors can accomplish these requirements by providing information to controllers as individual process variables.
Extensively used in industrial and manufacturing applications, in consumer devices and electronic products, proximity sensors are used mostly for safety and inventory management applications.
Working principle of a proximity sensor
A proximity sensor senses an object by checking its surrounding electromagnetic field. An electromagnetic field or electromagnetic radiation beam is emitted, and the sensor checks for a change in the field or return signal. If there is an object in the way, the return signal changes, confirming the presence of an object in its surroundings.
What are the features of a proximity sensor?
Contactless sensing: As proximity sensors can be used to detect an object without physically touching it, no damage is done to the object.
Not affected by the surface condition or surface colour or surface texture of the object: Proximity sensors receive the return signal without being affected by the physicality of the object.
Suitable for harsh environments: Proximity sensors can be used in damp or dirty or oily locations. These sensors can even be used under both high and low temperature conditions (−40 to 200°C).
High-speed response: As opposed to switches that require physical contact, proximity sensors respond quickly.
Longer service life: A proximity sensor has no moving parts and only uses semiconductor outputs. This gives the sensor a longer service life.
Types of proximity sensors
Inductive proximity sensors: These proximity sensors are used to detect only metallic or ferrous objects by using the inductive properties of a metal. Metals have inductive properties, which change the properties of a field when they are in close proximity, alerting the proximity sensor to the presence of metals. These proximity sensors have a high switching rate, are highly accurate, and can withstand harsh environments.
Capacitive proximity sensors: Not limited to metallic targets, capacitive proximity sensors work on the principle of a capacitor. The sensor consists of a plate, oscillator, threshold detector and an output circuit. The capacitance increases when an object approaches the plate, which triggers the detector circuit. They are usually inexpensive, feature high resolution, are stable, fast, and require very little energy.
Photoelectric proximity sensors: Photoelectric proximity sensors have an emitter that sends a beam of light towards a detector. When the target is between the emitter and detector, it is detected. In addition to low cost, installation is simple, the range of the sensor is longer and they can be used in unfavourable conditions.
Ultrasonic proximity sensors: The ultrasonic proximity sensor detects whether a target component is present or not using reflected or transmitted ultrasonic waves. They are capable of operating in a wide variety of operating conditions.
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