Today, it is difficult to imagine modern automation systems without advanced proximity sensors. Such elements play a key role in many devices, and their use is limited only by the ingenuity of engineers. There are several types of proximity sensors, including: inductive sensors, laser and optical sensors, ultrasonic sensors, magnetic sensors and capacitive sensors. What are their characteristics and what is their use? Check!
From this article you will learn:
- What is the principle of operation of the 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 about the rapid development of computers and IT, but also of automation. However, more and more advanced devices need more and more different types of sensors. They include 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 in Onninen
Inductive sensors
The first models of such sensors appeared in the 1960s and are still among the most frequently installed in automation systems. This type of 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 short distance from the sensor. Inductive proximity sensors may differ in housing and type. However, the structure of each inductive sensor consists of the following parts:
- coil,
- oscillator,
- detection circuits,
- output circuits.
What is the working principle of the inductive proximity sensor? In such sensors, alternating current is generated by an oscillator and then passes through a coil, generating a magnetic field. The active surface of the sensor depends on the direction of mounting the coil. When a metal object appears in the sensor's detection field, it creates a magnetic field directed opposite to the field generated by the coil. This causes the oscillation amplitude 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 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 as a function of the sensor range. This is the difference in distance to which the inductive sensor responds when moving the metal closer to or 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 coefficient (range reduction) – a scale of material coefficient values is used for this type of sensors. It determines the approximate range of the inductive sensor on a given material.
- sensor face – how the sensor face is built is also very important. This determines whether the sensor's range will be larger or smaller. The enclosed face of an inductive proximity sensor usually has a shorter range but a more precise connection point. In turn, unbuilt sensor faces have a larger range, but a less precise connection point.
- Degree of protection (intended purpose and resistance of the sensor) – determining under what conditions and where proximity sensors can be used.
Optical and laser sensors
Another type of proximity sensors 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 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 respond quickly and are characterized by a very long 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 an object, using reflection from a reflector on an object (an 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 other beams are ignored ). Some models operate using the so-called barriers (transmitter and receiver separated). Object detection occurs when this object interrupts the beam between two modules. There are also optical sensors available on the market that use LEDs instead of a laser diode (e.g. XUX1ARCNT16 SCHNEIDER). However, the principle of operation of the optical sensor is similar to the laser version.
Proximity ultrasonic sensors
Ultrasonic sensors are definitely a solution that is at least 30 years younger than, for example, optical or inductive sensors. In ultrasonic sensors (e.g. Banner QS18UPAQ8), the ultrasound wave is emitted towards the detected objects. When this wave actually hits an object, it reflects off it and returns to the sensor. However, the problem in this case is that ultrasound can also be reflected from objects that are not the object of measurement (for example, the machine housing). Therefore, to avoid falsifying the measurement, the time that passes from sending to receiving the wave is counted. When this time is shorter than previously assumed, the sensor will assume that it has detected the object, when it is longer - it has been reflected from a machine or wall. Ultrasonic proximity sensors have many advantages, including: they are resistant even to heavy dirt, can work immersed in liquid, and detect various types of objects.
Magnetic proximity sensors
Magnetic sensors (e.g. Electronic MZ070186) are among the simplest proximity sensors. Their principle of operation is to control the contacts under the influence of a magnetic field, the source of which may be an electromagnet or a permanent magnet. Depending on the sensor model, the contacts can be designed to carry small currents or large inductive loads. Unlike other proximity sensors, magnetic sensors have 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 in difficult operating conditions.
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, one should take into account 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 both to detect metallic objects and other types of obstacles (water, wood, plastic, etc.). The ability to detect plastic objects in particular makes capacitive sensors willingly installed 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 capacity 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 signals the oscillator to work. Whether the frequency has decreased or increased is detected by the detection circuit and activates the amplifier to power the relay contacts.
A big 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 what material the detected object is made of.
Additionally, capacitive sensors are exceptionally resistant to interference, such as dust, aerosol in the air, or electromagnetic influence. For this reason, capacitive proximity sensors are used in various industries - food, automotive, as well as warehouse and mobile technologies.
Proximity sensors in the Onninen offer
There are various types of proximity sensors available on the market, and manufacturers compete with each other in innovative design solutions. This makes it possible to easily select the appropriate sensor for a given automation system and fully use its capabilities. You can choose proximity sensors depending on your preferences. You can choose from, among others: capacitive sensor, inductive sensor, laser or optical sensor, ultrasonic sensor, magnetic sensor. Check out the offer of proximity sensors at the Onninen electrical wholesaler and choose a product tailored to your needs!