An Omron proximity sensor detects the presence of an object. Proximity sensor can be categorised as a non-contact type of sensor. That is why proximity sensors do not need to contact an object in order to detect it. Proximity sensors may be implemented using various techniques such as Optical (such as Infrared or Laser), Ultrasonic, Hall Effect, Capacitive etc. There are also various types of proximity sensor such as inductive, capacitive, ultrasonic, and IR.
Types of Proximity Sensors
1. Inductive Proximity Sensors
Inductive proximity sensors are mainly used to detect objects that are metals since they are contactless sensors. If metallic-based objects get near to it, The inductive proximity sensors will drive a coil with an oscillator. This is based on the famous law of induction. There are four components of inductive proximity sensors, which are output switching circuit, oscillator, coil, and schmitt trigger.
There are two versions of inductive proximity sensors which are shielded and unshielded. Shielded inductive proximity sensors have a higher concentration of generated electromagnetic fields in the front. Sensor coil’s sides are also covered up (hence shielded). While for the unshielded inductive proximity sensor, the generation of electromagnetic fields by the coil is unrestricted. This makes the sensing distances of an unshielded inductive proximity sensor wider and greater than the shielded one.
Inductive proximity sensors work in three ways. First, the coil will be supplied with an alternating current. This will make the coil generate an electromagnetic detection field. Second, coil inductance changes will happen when eddy current is built-up. This will happen if the distance between a metallic object is close to the magnetic field. Lastly, the output switch for the sensor will be triggered when the coil induction made some changes.
2. Capacitive Proximity Sensors
Different from inductive, capacitive proximity sensors detect both non-metallic and metallic objects. It can detect non-metallic objects such as granular, liquid and powders. Capacitive proximity sensors work by detecting any changes in it’s capacitance. The components of capacitive proximity sensors are almost the same as inductive. However, they do not have coils and have 2 charging plates instead.
To detect an object, a capacitive proximity sensor will be producing an electrostatic field. Next, the capacitance of the plates will be increasing if an object is near to the sensing area. This will result in the gaining of oscillator amplitude. Lastly, the output switch of the sensor will be triggered by the gain of the amplitude.
3. Ultrasonic Proximity Sensors
Ultrasonic proximity sensors, on the other hand, use high-frequency ultrasonic range to detect the presence of objects. It is able to do so by converting electrical energy. It can also detect the same objects as the capacitive proximity sensors. Ultrasonic proximity sensors only consist of an ultrasonic receiver and ultrasonic transmitter.
Firstly, sonic waves are emitted by the ultrasonic transmitter. Second, the emitted sonic waves will bounce off any nearby objects. Third, if there is an object and the sonic waves have already bounced off it, the same wave will then go back and thus be received by the ultrasonic receiver. Lastly, the distance will be calculated by taking into account the time it took for the sound waves to be emitted and received.
4. Infrared Proximity Sensors (IR)
Infrared (IR) proximity sensors emit a ray of infrared light in order to detect an object. The process of infrared proximity sensors is almost the same as the ultrasonic sensor, with the difference that IR sensor emits infrared light instead of sonic waves. The main component of IR proximity sensor is that it has a light detection and an infrared LED.
The process of detecting an object for an IR proximity sensor is that it emits infrared light from the infrared LED. Next, the infrared light is reflected back to the sensor once it hits an object. Lastly, the light detector will detect the reflected light and begin to determine the distance of the object.