4 types of proximity sensors
The working principle of inductive proximity sensors is to use electromagnetic fields, so they can only detect metal targets. When a metal target enters an electromagnetic field, the induction characteristics of the metal will change the properties of the magnetic field, thereby alerting the proximity sensor to the presence of the metal target. Based on the degree of metal induction, targets can be detected at larger or shorter distances. Due to the limitation of the magnetic field, the sensing range of the induction sensor is relatively narrow, averaging from a few millimeters to 60 millimeters. However, the limitations of inductive sensors in terms of range have been compensated for in terms of environmental adaptability and diversity of metal induction.
Due to the absence of wear on moving parts, inductive proximity sensors have a longer lifespan. However, it should be noted that metal contaminants (such as files in cutting applications) can sometimes affect the performance of sensors. Therefore, inductive sensor housings are typically made of nickel plated brass, stainless steel, or PBT plastic.
2. Capacitive proximity sensor
Capacitive proximity sensors can detect metal and non-metal targets in powder, particle, liquid, and solid forms. This, combined with their ability to sense non-ferrous metal materials, makes them very suitable for observing glass monitoring, tank level detection, and hopper powder level recognition.
It is worth mentioning that there is a difference between inductive sensors and capacitive sensors: inductive sensors oscillate until a target is present, while capacitive sensors oscillate when a target is present.
3. Photoelectric proximity sensor
Optoelectronic proximity sensors have a wide range of applications and can detect targets with diameters as small as 1 millimeter or distances as large as 60 mm.
The most reliable photoelectric sensing is the reflective sensor. The transmitter is separated from the receiver by a separate casing, providing a constant beam of light. When the object passing between the two interrupts the light beam, detection will be performed.
Despite its high reliability, it is the least popular optoelectronic device. Because the installation of the transmitter and receiver in two opposite positions (which may be far apart) is both expensive and laborious.
The transmitter and receiver of a reflective proximity sensor do not have separate housings, but are both located in the same housing, facing in the same direction. The transmitter generates a laser, infrared, or visible light beam and projects it onto a specially designed reflector, which then deflects the beam back to the receiver. When the optical path is damaged or interfered with, detection will be carried out.
Like reflective sensors, the transmitter and receiver of diffuse sensors are located in the same housing. But since the detection target acts as a reflector, it detects light reflected from a distance.
4. Ultrasonic proximity sensor
Ultrasonic proximity sensors are used in many automated production processes. They use sound waves to detect objects, so color and transparency do not affect them. This makes them an ideal choice for various applications, including remote detection of transparent glass and plastic, distance measurement, continuous liquid and particle level control, and stacking of paper, sheet metal, and wood.
Ultrasonic diffuse proximity sensors use acoustic sensors that emit a series of acoustic pulses and then listen for the sound they return from the reflected target. Once the reflected signal is received, the sensor will send the output signal to the control device. The sensing range is extended to 2.5 meters.
Ultrasonic reflection sensors can detect objects within a specified sensing distance by measuring propagation time. The sensor emits a series of sound pulses that bounce off a fixed relative reflector (any flat hard surface, a machine, a board). The sound wave must return to the sensor within the time interval adjusted by the user. If not, it is considered that there is an object blocking the sensing path, and the sensor has correspondingly emitted an output signal. Because the sensor listens for changes in propagation time rather than just returning signals, it is ideal for detecting sound absorbing and deflecting materials such as cotton, foam, cloth and foam rubber.
Similar to a photoelectric sensor, the transmitter and receiver of an ultrasonic photoelectric sensor are located in separate housings. When an object destroys the sound beam, the receiver triggers an output. These sensors are ideal for applications that require the detection of continuous objects, such as transparent plastic nets. If the transparent plastic breaks, the output of the sensor will trigger the connected PLC or load.
