Proximity Sensors and Types
Proximity sensors are devices used across a wide range of industrial and manufacturing applications. Basically, they are made to sense the presence of objects and perform some action, or to simply flag their the presence or absence. At the core of their operation is that they can function as intended without touching the target. Hence, they’re also called non-contact sensors.
There are lots of general sensing techniques that proximity sensors are known to use. Such techniques work to categorize different sensor types on top of other relevant factors like the object that must be detected or the most conducive environmental conditions for detection by a certain sensor type.
Below are the most common types of proximity sensors being used these days:
As the term indicates, these sensors work by detecting a change in the capacitance, or the ratio of the change in an electric charge to the matching change in its electric potential as affected by an air gap or the presence of another material between two surfaces. Whenever an object to be detected lands in the sensor’s field, there will be a change in capacitance, which will be interpreted by the sensor as the presence of that object.
These sensors are based on varying inductance, or the process of inducing a voltage in one conductor after another conductor’s current changes. But due to their inductive action, these sensors are only compatible with metallic items.
In addition, the type of object sensed will affect the sensing distance. For instance, ferromagnetic materials such as steel usually have the longest sensing distances compared to other metals like aluminum and copper.
These sensors are based on light, meaning they sense the presence or absence of objects according to variations in the amount of light. Reflective and through-beam are two key types of photoelectric sensors. Reflective sensors emit a beam of light that hits the object and is reflected back to the sensor, often in the same physical container as the emitter beam. On the other hand, through-beam sensors have two independent units: an emitter or light source and a separate receiver or sensor. Every time an object breaks the light beam, the sensor takes note.
Finally,ultrasonic sensors depend on sound waves to detect the presence of objects. These detectors emit a high frequency sound wave (inaudible to humans) which goes back to the sensor as it hits an object, where the object’s distance can be calculated based on how long the sound wave was reflected. As such, these sensors are used to measure the distance of objects, like in automotive park-assist and in filling applications where fluid levels must be detected as part of the process.