These sensors are responsible to detect objects. As we know object detection is a critical task in the automation industry. Whether detecting the presence of the object passing by on conveyors, the closure of the door, etc. it is still difficult to detect the object.
There are many different object sensing technologies are being used nowadays, some of them are using machine learning to achieve their goals. Here we are going to present a brief description of some object sensors:
This kind of object sensor is a basic electromechanical switch. These devices contain a sensitive micro switch that changes its state in contact with the object. Physical contact with the target object is not always possible or desirable that is a limitation in this object sensor.
Pneumatic-type object sensors utilize compressed air and a sensitive diaphragm valve to detect the presence of the object. Compressed air streams from a very narrow perforation until any object blocks the stream. Blocking of the air stream creates a minute change in air pressure and this change is being detected by a downstream diaphragm switch that produces an electrical control signal for the control circuit.
These object sensors are using two basic principles. The first one is Reed contact and the second one is Hall effect transducer. In both cases, the presence of a magnetic field produces a change of state in an electrical signal. The failure rate of Reed switches is high as compare to Hall switched. That’s why many designers preferred Hall switches over Reed switches.
Inductive object sensors are also known as proximity switches that detect a disruption in the magnetic fields due to the presence of any metallic object. The reliable detection distance varies and it depends on the type of the metal and also the amount of the metal that comes into the sensor range. These sensors come in several sizes and shapes. One main limitation of an inductive object sensor is that it detects metallic objects only.
This kind of sensor comes under a type of proximity switch. These proximity switches detect non-metallic objects that have dielectric constant different from air. This property makes them ideal to detect various objects like wood, plastics, liquid, fabric, etc. Once the target object comes into the range of this sensor, electrostatic fields between capacitive plates change abruptly.
Photoelectric type object sensors use different technologies depending on their application. But they all use the same principle. They all send out a light beam and then detect a change in reflected light intensity. Laser sensors have come into this category and they can send light beam 50 meters or longer. Transparent objects, or objects with a varying surface finish, can be problematic for photoelectric type object sensors.
These devices transmit a short burst of ultrasonic sound waves toward the target object and that object reflects the sound back to the sensor. The sound wave is reflected by almost all kinds of solid materials and it does not affect by color or other optical effects.