Inductive sensors have a series of advantages such as simple structure, reliable operation, high measurement accuracy, stable zero point, large output power, etc. Its main disadvantage is that sensitivity, linearity, and measurement range are mutually restricted, and the frequency response of the sensor is low, so it is not suitable for rapid dynamic measurement. There are many types of inductive sensors, including self-inductance sensors , mutual inductance sensors , and eddy current sensors.
The self-inductance sensor consists of a coil, a core, and an armature. The core and armature are made of silicon steel and other magnetic materials.
Structure of self-inductance sensor. The self-inductance sensor converts measured change into self-inductance L change and converts it into voltage or current output through a certain conversion circuit.
When the sensor is in use, the moving part of the sensor is connected with the moving core armature. When the moving core moves, the thickness of the air gap between the core and the armature will change, which will cause the change of magnetic circuit reluctance and the change of coil inductance value.
As long as the change of inductance is measured, the magnitude and direction of the displacement of the moving core can be determined. Working principle of self-inductance sensor. Variable air gap type self-inductance sensor. Variable air gap type self-inductance sensor structure. Variable area type self-inductance sensor. Variable area type self-inductance sensor structure. Solenoid type inductive sensor.
When the sensor works, the variation of armature length in the coil will cause the variation of the inductance of the coil. The sensor is simple in structure, easy to make and low in sensitivity, which is suitable for measuring large displacement. Because there is an AC excitation current in the coil, the armature is always subjected to electromagnetic suction, which will cause vibration and additional error.
The output error will be caused by external interference, the change of power supply voltage frequency, and temperature. In practice, two identical sensor coils often share one armature to form a differential self-inductance sensor, and the electrical parameters and geometric dimensions of the two coils are exactly the same.
This structure can not only improve linearity and sensitivity but also compensate for the influence of temperature change and power supply frequency change, to reduce the error caused by external influence.
Structure of differential self-inductance sensor. Features of differential self-inductance sensor. The differential air gap inductance sensor is composed of two identical inductance coils 1, 2, and magnetic circuits. During measurement, the armature is connected to the measured displacement through the measuring rod. When the measured body moves up and down, the guide rod drives the armature to move up and down with the same displacement, so that the magnetic resistance in the two magnetic circuits is equal and the direction changes in the opposite direction.
Then the inductance of one coil to increase and the inductance of the other coil to decrease, forming a differential form. The characteristic curve of the self-inductance coefficient is shown in the figure. Self-inductance characteristic curve. The sensor that converts the measured non-electric quantity change into the mutual inductance change of the coil is called the mutual inductance sensor.
The sensor is made according to the basic principle of the transformer, which converts the measured displacement into the change of mutual inductance between primary and secondary coils. When the primary coil is connected with the excitation power, the secondary coil will generate the induced electromotive force. When the mutual inductance between the two changes, the induced electromotive force will also change accordingly. Because two secondary coils use a different connection method, it is called a differential transformer type sensor, referred to as a differential transformer.
There are many types of differential transformers, such as variable gap type, variable area type, and spiral pipeline type. The differential transformers of A and B structures are all plate-shaped with high sensitivity and narrow measuring range, which are generally used to measure the mechanical displacement of several microns to several hundred microns.
For the measurement of displacement between 1mm and hundreds of mm, cylindrical armature solenoid type differential transformers are often used, such as C and D structures. The e and F structures are differential transformers that measure the angle of rotation, and the tiny displacement of a few seconds can usually be measured. It can be measured within the scope of the mechanical displacement and has high measurement precision, high sensitivity, simple structure, reliable performance, etc.
The structure of the differential transformer consists of an iron core, armature, and coil. Its structure has many forms, but its principle of operation is basically the same. There is a primary coil 1 and a secondary coil 2 in the upper and lower iron cores of the differential transformer.
The upper and lower primary coils are connected in series with an ac excitation voltage, and the two secondary coils are connected in series according to the potential. Schematic diagram of three-stage solenoid differential transformer. Magnetic objects and non-magnetic objects Remember that magnetic objects are easily attracted by a magnet, whereas non-magnetic objects are not.
Catalog Download. What Is a Sensor? A Comprehensive Look at Sensors. Learn all about the principles, structures, and features of eight sensor types according to their detection principles. For this purpose, in Chapter 7, the book author proposes a generic functional diagram see the following figure , which should universally be valid for the very large diversity of ISs. The functional blocks and their composing electronic stages are solely defined by showing their functionality.
The implementation and integration levels of this functional diagram starting with historical discrete circuitries on transistor level and ending with future-oriented software defined sensors SDS are subjects of the following Chapters, 8 to Review and order the book Inductive Sensors for Industrial Applications. Generic functional diagram, universally valid for the very large diversity of inductive sensors IS.
The first sensor fundamental part, namely the inductive sensing element ISE, is elaborately presented in book Chapters 4 to 6. The ISE is now figuratively depicted in the generic functional diagram by the entity of three inductors see below. In the large majority of cases, the ISE contains a resonance circuit, which consists of the sensing coil and of a resonance capacitor, like in the generic diagram. The second sensor part i.
The first, namely the front-end electronics FEE, marks the low signal and high sensitivity unit of every sensor. Furthermore, the FEE usually consists of the following electronic stages :. To maintain the generic character, the BEE structure above contains two parallel signal paths: an analogue one and a digital one, which can coexist.
However, usual sensors contain either of them. The power supply and protections PSP is an essential functional unit of any sensor installed in. In the figure above, this block PSP is a placeholder not only for sensor internal supplying but also for sensor internal protection functions, which are mandatory for industrial sensor implementations.
The inventory list of these tasks contains:. The digital control unit DCU is an advanced functional unit, which belongs to modern, state-of-the-art IS. As a result of sensor specific constraints low costs, limited free space inside the sensor housing, low current consumption, etc.
Due to the wide spread of the inductive proximity sensors IPSs for industrial automation applications over the last 50 years, their evaluation electronics was continuously developed and integrated on a larger and larger scale. In addition, the involved silicon foundries and also their applicants, namely the sensor manufacturers, willingly published these technological steps.
Correspondingly, the evolution was partially open. With this rich volume of information, it was possible to elaborate in the book a morphological map Figure 7. Types of inductive sensors. Inductive sensors are available in a lot of different configurations.
They also make inductive sensors for hazardous, high-temperature, and washdown locations. For washdown locations, we need to use a shielded inductive sensor. The Advantages of an inductive sensor. Here are some advantages of using inductive sensors compared to other types of sensors.
Inductive sensors are solid-state and do not have any moving parts. Inductive sensor mounting. Inductive sensor applications. Search for:. Adam Stykemain. Automation Engineer. Posted on June 30th, Checkout your email. Have questions? Sign in. Contact Us.
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