Proximity sensors are use in various devices. From the basic household applications to large scale applications proximity sensors have a vast range of applications. The basic functionality of the proximity sensors is the detection of the objects. The detection of material or an object by the proximity results in an initiation of a specific action. The action initiated upon detection is pre-defined. The detection of the object with the help of proximity sensor is without any physical contact of the sensor with the object. A number of sensing techniques are utilize in the proximity sensor for its operation.
Types of Proximity Sensors:
The proximity sensors are categorized in different categories as per their detections. Some proximity sensors are use to detect materials whereas some are use to detect different environmental conditions upon these classifications proximity sensors types are as follow:
The capacitive proximity sensors uses the variance in the capacitance of the sensor to conclude that an object has been detected. The mechanism for this category is quite simple in which the sensor act as a separate plate of the capacitor and the object acts as another plate or voltage source for the object. The air is the dielectric material between these two potentials. As soon as the object enters the dielectric of the plates, the capacitance of the capacitor changes. This change is taken as detection of object.
The inductive type proximity sensors are operated on the change in the inductance of the sensor. This type of proximity sensors is used with the metallic objects. With the changing current in the conductor the inductance of the circuit is also varied. This change in inductance triggers that an object was detected. Objects having non-conductive properties cannot be detected by these proximity sensors. The type of the material detected can affect the range of these sensors as different materials have different conduction properties.
Detection Principle of Inductive Proximity Sensors
Inductive Proximity Sensors detect magnetic loss due to eddy currents that are generates on a conductive surface by an external magnetic field. An AC magnetic field generates on the detection coil, and changes in the impedance due to eddy currents generated on a metallic object are detected.
Other methods include Aluminum-detecting Sensors, which detect the phase component of the frequency, and All-metal Sensors, which use a working coil to detect only the changed component of the impedance. There are also Pulse-response Sensors, which generate an eddy current in pulses and detect the time change in the eddy current with the voltage induced in the coil.
Detection Principle of Capacitive Proximity Sensors
Capacitive Proximity Sensors detect changes in the capacitance between the sensing object and the Sensor. The amount of capacitance varies depending on the size and distance of the sensing object. An ordinary Capacitive Proximity Sensor is similar to a capacitor with two parallel plates, where the capacity of the two plates is detected. One of the plates is the object being measured (with an imaginary ground), and the other is the Sensor’s sensing surface. The changes in the capacity generated between these two poles are detected.
The objects that can be detected depend on their dielectric constant, but they include resin and water in addition to metals.
Applications of Proximity Sensors
Proximity sensors have number of applications. The very basic is the detection of objects. This application of proximity is hugely use. For example in cell phones the proximity sensors are the essential parts. In different projects of engineering different proximity sensors are use for various functionalities. Proximity sensors are also use in parking lots, sheet break sensing and conveyor systems.