In modern machine tools and high-precision equipment, where it is important to control the position of structural elements, an inductive sensor is installed. What this device is used for, what types and methods of connection exist, how it works, we will consider in this article.
Appointment
An inductive sensor is designed to control the movement of the working body without direct contact with it. The main area of application for it is machine tool equipment, precision medical devices, automation systems for technological processes, measurement and control of product shape. In accordance with the provisions of clause 2.1.1.1 of GOST R 50030.5.2-99, this is a sensor that creates an electromagnetic field in the sensitivity area and has a semiconductor switch.
The scope of application of inductive sensors is largely determined by their high reliability and resistance to external factors. Their readings and performance are not affected by many environmental factors: moisture, condensation, accumulation of dust and dirt, ingress of solid particles. Such features are provided by their device and design data.
Device
The development of the radio electronics segment has led not only to the improvement of the initial mechanisms, but also to the emergence of fundamentally new inductive sensors. As an example, consider one of the simplest options (Figure 1):
As you can see in the figure, it includes:
- magnetic circuit or yoke (1) - designed to transmit the electromagnetic field from the generator to the sensitivity zone;
- inductor (2) - creates an alternating electromagnetic field when an electric current flows through the loops;
- measuring object (3) - metal anchor inserted or moved in the area of sensitivity, non-metallic objects not capable of influencing the state of the electromagnetic field, therefore they are not used as detector;
- the gap between the object of measurement and the main magnetic circuit (4) - provides a measure of interaction as a magnetic dielectric, depending on the sensor model and the method of movement, it can remain unchanged or fluctuate in a given range;
- generator (5) - designed to generate an electric voltage of a given frequency, which will create an alternating magnetic field in a given area.
Principle of operation
The principle of operation of an inductive sensor is the ability of the electromagnetic field to change its parameters, depending on the value of the magnetic conductivity along the path of the flow. Its operation is based on the classic version of a coil wound on a core.
When an electric current I flows through the turns of this coil, a magnetic field is generated (see. Figure 2), the resulting vector of magnetic induction B of which is determined by the rule of the Right hand. When the magnetic field moves through the core, the ferromagnetic material provides maximum throughput. But, as soon as the lines of magnetic induction enter the air space, the magnetic conductivity deteriorates significantly and part of the field is dissipated.
When a triggering object (Figure 3) made of metal is introduced into the field of the inductive sensor, the intensity of the induction lines changes sharply. As a result, the flux increases and its value changes, and this, in turn, leads to a change in the electrical quantity in the coil circuit due to the phenomenon of mutual induction. In practice, this signal is too small, so an amplifier is included in their circuit to expand the measurement range of the inductive sensor.
Sensing distance and target
Depending on the design and principle of operation of the inductive sensor, the target object can have vertical or horizontal movement relative to the meter itself. However, the reaction of the sensor to the beginning of the movement of the controlled object may not start immediately, which is due to nominal distance at which the sensor's sensitivity zone and technical parameters are provided object.
As you can see in Figure 4, in the first position, the controlled object is located at such a distance where the electromagnetic lines do not reach its surface. In this case, the signal will not be removed from the inductive sensor, since it does not register movements in the sensitivity zone. In the second position, the controlled object has already crossed the sensing distance and entered the sensitive area. As a result of interaction with the object, a corresponding signal will appear at the sensor output.
Also, the sensing distance will depend on the geometric dimensions, shape and material. It should be noted that only metal objects are used as an object for triggering an inductive sensor. but the moment of transition of the sensor to the opposite state will also differ from the specific type, which is shown in diagram:
P.S. Read more in our article: https://www.asutpp.ru/induktivnyy-datchik.html