It is hard to imagine modern automation systems today without advanced proximity sensors. Such elements play a key role in many devices, and their use is limited only by the ingenuity of engineers. Proximity sensors include several types, including: inductive sensors, laser and optical sensors, ultrasonic sensors, magnetic sensors, and capacitive sensors. What are their characteristics and what are their applications? Check it out!
In this article you will learn:
- What is the operating principle of a proximity sensor?
- How do inductive sensors work?
- How do laser and optical sensors work?
- How do ultrasonic sensors work?
- How do magnetic sensors work?
- How do capacitive sensors work?
What are proximity sensors used for?
The 21st century is not only a rapid development of computers and IT, but also automation. However, increasingly advanced devices need more and more different types of sensors. Among them, we can find both simple sensors , whose basic task is to signal presence, as well as very advanced sensors for processing three-dimensional images. However, automation most commonly uses proximity sensors . What are they for? Their basic task is to signal the presence of an object in a non-contact way. The most popular types of proximity sensors are listed below.
Proximity sensors at Onninen
Inductive sensors
The first models of such sensors appeared in the 1960s and are still among the most popular in automation systems. Such inductive sensors (e.g. Truck BI2-EG08-AN6X-V1131) are perfect when it is necessary to detect an element made of metal at a very small distance from the sensor. Inductive proximity sensors may differ in housing and its type. However, the construction of each inductive sensor consists of the following parts:
- coil,
- oscillator,
- detection circuits,
- output circuits.
What is the operating principle of an inductive proximity sensor? In such sensors, an alternating current is generated by an oscillator and then passes through a coil, generating a magnetic field. The direction of the coil installation determines where the active surface of the sensor is located. When a metal object enters the sensor's detection field, it generates a magnetic field directed opposite to the field generated by the coil. This causes the amplitude of the oscillations to decrease and is detected by the detection circuit. In this way, the output circuits are activated. Proximity sensors of this type are most often used in the industrial sector.
The housings of inductive sensors can be very different, but the most popular and most frequently purchased are cylindrical sensors (e.g. XSAV11373 SCHNEIDER).Inductive proximity sensors can detect various types of metals.
When choosing an inductive sensor, you should pay attention to such parameters as:
- sensor range – is usually expressed as the maximum range of the inductive sensor. It depends on what metal the detected object is made of.
- hysteresis – most often expressed as a percentage value, included in the sensor range function. This is the difference in distance to which the inductive sensor responds when approaching or moving away from the sensor face. The hysteresis value mainly depends on the type and size of the sensor and usually does not exceed 20% of the measurement range.
- material factor (range reduction) – a scale of material factor values is used for this type of sensor. It determines the approximate range of the inductive sensor for a given material.
- sensor face – how the sensor face is built up is also very important. This determines whether the sensor range will be longer or shorter. The built-in face of an inductive proximity sensor usually has a shorter range, but a more precise connection point. On the other hand, unbuilt sensor faces have a longer range, but a less precise connection point.
- Degree of protection (purpose and resistance of the sensor) – definition of the conditions in which and where proximity sensors can be used.
Optical and laser sensors
Another type of proximity sensor is photoelectric sensors, in which the light source is, for example, laser diodes (e.g. Banner QS18VP6LAF). Manufacturers often use light beam modulation, which significantly reduces interference and energy consumption. Most often, we can find laser proximity sensors on the market, in which the transmitter is combined with the light source, although there are also models with separate modules. Thanks to laser sensors, it is possible to detect even very small objects and even their minimal movements. These types of sensors react instantly and are characterized by a very large detection range. On the other hand, the high sensitivity of laser sensors to contamination may be a problem. On the market, we can find laser sensors using direct reflection from the object, using reflection from a reflector on the object (the object is detected when it covers the emitted light beam), using reflection of polarized light (it only reacts to a beam from a previously determined direction, and the remaining beams are ignored). Some models operate using the so-called barriers (separated transmitter and receiver). Detection of an object occurs when this object interrupts the beam between two modules. Optical sensors are also available on the market, which use LED diodes instead of a laser diode (e.g. XUX1ARCNT16 SCHNEIDER). The principle of operation of the optical sensor is similar to the laser version.
Ultrasonic proximity sensors
Ultrasonic sensors are definitely a younger solution, at least 30 years younger than optical or inductive sensors. In ultrasonic sensors (e.g. Banner QS18UPAQ8), an ultrasound wave is emitted in the direction of detected objects. When this wave actually hits the object, it reflects off it and returns to the sensor. In this case, however, the problem is that ultrasound can also reflect off objects that are not the subject of measurement (e.g. machine housing). Therefore, to avoid falsifying the measurement, the time that elapses from sending to receiving the wave is counted. When this time is shorter than previously assumed, the sensor will consider that it has detected the object, when it is longer - the reflection occurred from the machine or wall. Ultrasonic proximity sensors have many advantages, including being resistant even to large amounts of dirt, they can work immersed in liquids, and they detect various types of objects.
Magnetic proximity sensors
Magnetic sensors (e.g. Electronic MZ070186) are among the simplest proximity sensors. Their operating principle is based on controlling contacts under the influence of a magnetic field, the source of which can be an electromagnet or a permanent magnet. Depending on the sensor model, the contacts can be adapted to conduct small currents or to large inductive loads. Unlike other proximity sensors, magnetic sensors are characterized by a simple structure, there is no electronics that could break down. Due to the fact that magnetic proximity sensors are characterized by high resistance to dust and high temperatures, as well as magnetic vibrations, they can be used where operating conditions are difficult.
Such proximity sensors also have high resistance to overloads and overvoltages, and the sensors can be used in various automation systems (e.g. for pneumatic actuators). However, it is necessary to reckon with the low sensitivity of such sensors and the need to use magnets or electromagnets.
Capacitive proximity sensors
Capacitive sensors (e.g. L80. CDWM3020ZPM SELS) can be used to detect both metallic objects and other types of obstacles (water, wood, plastic, etc.). The ability to detect plastic objects in particular makes capacitive sensors popular in packaging machine systems, but they are also used, for example, to detect when a tank is filled with liquid, etc. This type of sensor works by measuring the change in capacitance between the object and the sensor. This creates a capacitor whose capacitance depends on the distance between the object and the sensor. When an object appears in the detection field, the capacitance of the capacitor increases, which gives a signal to the oscillator to work. Whether the frequency has dropped or increased is detected by the detection circuit and starts the amplifier that supplies the relay contacts.
A major advantage of capacitive sensors is the ability to easily set their sensitivity (working distance). This sensitivity depends on the size of the sensor, as well as the material of the detected object.
In addition, capacitive sensors are exceptionally resistant to interference, such as dust, aerosol in the air, or electromagnetic interference. For this reason, capacitive proximity sensors are used in various industries - food, automotive, as well as storage and portable techniques.
Proximity sensors in the Onninen offer
There are various types of proximity sensors to choose from on the market, and manufacturers are competing with each other in innovative design solutions. This means that you can easily select the right sensor for a given automation system and fully use its capabilities. You can choose proximity sensors depending on your preferences. You can choose from a capacitive sensor, an inductive sensor, a laser or optical sensor, an ultrasonic sensor, a magnetic sensor. Check out the range of proximity sensors at the Onninen electrical wholesaler and choose a product tailored to your needs!