Inductive sensor
Inductive sensors, also called eddy current sensors, are composed of three parts: an oscillator, a switching circuit and an amplifying output circuit. The oscillator generates an alternating magnetic field, and when the metal target approaches this magnetic field, and reaches the induction distance, eddy currents are generated in the metal target, which causes the oscillation to decay and even the vibration to stop. The changes of oscillator oscillation and stop vibration are processed by the post-amplifier circuit and converted into a switching signal, which triggers the drive control device, so as to achieve the purpose of non-contact detection. It can be seen that the object that can be detected by this proximity switch must be a conductor.
Capacitive sensor
The measurement of this sensor is usually one plate of the capacitor at which the sensor is fixed, and the other plate is usually grounded or connected to the housing of the device during the measurement process. When an object moves toward the sensor, regardless of whether it is a conductor, due to its proximity, the dielectric constant between the two plates of the capacitor will always change, so that the capacitance of the capacitor will change, so that the state of the circuit connected to the measuring head will also change, thus achieving the purpose of non-contact detection. The objects detected by this proximity switch are not limited to conductors, liquids or powders that can be insulated.
Hall-style sensors
When a sheet of metal or semiconductor with an electric current is placed vertically in a magnetic field, the two ends of the sheet produce a potential difference, which is called the Hall effect. The potential difference between the two ends is called the Hall potential U, and its expression is U=K·I·B/d, where K is the Hall coefficient, I is the current passing through the sheet, B is the magnetic induction intensity of the applied magnetic field (Lorrentz force), and d is the thickness of the sheet.
It can be seen that the sensitivity of Hall effect is directly proportional to the magnetic induction intensity of the applied magnetic field. Hall element belongs to this kind of active magnetoelectric conversion device, which is a magnetic sensitive element. It is based on the principle of Hall effect, the use of integrated packaging and assembly process made, it can easily convert the magnetic input signal into the actual application of electrical signals, but also has the practical application of industrial applications easy to operate and reliability requirements. The Hall switch is made of this characteristic of the Hall element. Its input is characterized by the magnetic induction intensity B. When the value of B reaches a certain degree (such as B1), the trigger inside the Hall switch flips, and the output level state of the Hall switch flips accordingly. The output is generally transistor output, and other sensors are similar to NPN, PNP, normally open, normally closed, latched (bipolar), dual-signal output points. Hall switch has the characteristics of no electric shock, low power consumption, long service life, high response frequency, the internal use of epoxy resin seal into an integrated, so it can work reliably in all kinds of harsh environments.
When the magnetic object moves close to the Hall switch, the Hall element on the detection surface of the switch changes the internal circuit state of the switch due to the Hall effect, which identifies the presence of a magnetic object nearby, and then controls the on or off of the switch. The detection object of this proximity switch must be a magnetic object.
Photoelectric sensor
Photoelectric sensors make use of the photoelectric effect. The light-emitting device and the photoelectric device are installed in the same detection head in a certain direction. When a reflective surface (detected object) approaches, the photoelectric device receives the reflected light and outputs it in the signal, thus it can "sense" that an object is approaching.
The photoelectric proximity switch made of photoelectric sensor can detect various substances, but the error of fluid detection is large.
Pyroelectric sensor
The pyroelectric sensor can sense the temperature change, and the pyroelectric part is installed on the detection surface of the switch. When an object with different ambient temperature approaches, the output signal of the pyroelectric sensor changes, and the approach of the object can be detected by converting the output signal of the sensor.
Linear proximity sensor
Linear proximity sensor is a linear device that belongs to metal induction, after the power is switched on, an alternating magnetic field will be generated on the sensor's induction surface, when the metal object is close to the induction surface, the metal will produce eddy current and absorb the energy of the oscillator, so that the oscillator output amplitude is linearly attenuated, and then according to the attenuation change to complete the purpose of contactless detection of the object.
The proximity sensor has no sliding contact, is not affected by non-metallic factors such as dust when working, and has low power consumption, long life, and can be used in a variety of harsh conditions. The linear sensor is mainly used in the intelligent control of analog quantity in the production line of automation equipment.
