Inductive sensors operate on the principle of electromagnetic induction, converting a measured quantity, such as displacement, into a change in inductance. Inductive sensors offer advantages such as simple structure, reliable operation, high measurement accuracy, zero-point stability, and relatively high output power. Their main disadvantages are the mutual constraints between sensitivity, linearity, and measurement range; low frequency response; and unsuitability for rapid dynamic measurements.
I. Classification of Inductive Sensor Devices
Inductive sensors are classified into three types: self-inductance sensors that change the air gap thickness δ, i.e., variable gap inductive sensors; self-inductance sensors that change the air gap cross-section S, i.e., variable cross-section inductive sensors; and self-inductance sensors that change both the air gap thickness δ and the air gap cross-section S, i.e., solenoid inductive sensors.
Variable gap type inductive sensor
The air gap δ of this sensor changes with the measurement, thus altering the magnetoresistance. Both its sensitivity and nonlinearity decrease as the air gap increases, so a balance must often be struck. δ is typically chosen between 0.1 and 0.5 mm.
Change area type inductor sensor
The relative coverage area (i.e., magnetic flux cross-section) between the core and armature of this type of sensor changes with the measurement, thus altering the magnetic reluctance. Its sensitivity is constant, and its linearity is excellent. This is a solenoid-type inductive sensor. It consists of a solenoid coil and a cylindrical armature connected to the object being measured. Its working principle is based on the change in magnetic reluctance along the leakage path of the coil's magnetic field lines. As the armature moves with the object being measured, it changes the inductance of the coil. This type of sensor has a large measuring range, low sensitivity, simple structure, and is easy to manufacture.
Solenoid-type inductive sensor
It consists of a solenoid coil and a cylindrical armature connected to the object being measured. Its working principle is based on the change in magnetic reluctance along the leakage path of the coil's magnetic field lines. As the armature moves with the object being measured, it changes the inductance of the coil. This sensor has a large measuring range, low sensitivity, simple structure, and is easy to manufacture.
II. Applications of Inductive Sensor Devices
Sensors, as tools for collecting and acquiring information, play a crucial role in the automated detection and quality monitoring of systems. Inductive sensors, a type of mutual inductance sensor, can convert minute geometric changes in non-electrical physical quantities such as displacement, vibration, and pressure (e.g., length, inner diameter, outer diameter, non-parallelism, non-perpendicularity, eccentricity, ellipticity) into minute changes in electrical signals. These changes are then converted into electrical parameters for measurement. As a highly sensitive sensor, it possesses advantages such as simple and reliable structure, high output power, strong impedance resistance, low requirements for the working environment, and good stability. Therefore, it is widely used in various engineering physical quantity detection and automatic control systems.
For example: using inductive displacement sensors to improve the precision of bearing manufacturing; using inductive micrometers to measure changes in minute and precise dimensions; achieving accurate measurement of the opening position of hydraulic valves; using flexible sensors for designing smart textiles; using inductive sensor principles to measure aperture taper error; using inductive sensors to detect abrasive particles in lubricating oil; using inductive sensors to monitor guide wheels of lifting devices, etc.
Inductive sensors can also be used as magnetic speed switches, gear tachometers, etc. These sensors are widely used in industries such as textiles, chemical fibers, machine tools, machinery, metallurgy, and automobiles for sprocket tooth speed detection, chain conveyor belt speed and distance detection, gear tachometers, and automotive safety system control. Additionally, these sensors can be used in feed pipe systems for small object detection, object ejection control, wire breakage monitoring, small parts differentiation, thickness detection, and position control.
Inductive displacement sensors utilize wires to form specific coil windings. The displacement is measured by the change in the self-inductance or mutual inductance of the winding coils caused by the change in the amount of displacement. Therefore, based on their conversion principle, inductive displacement sensors can be divided into two main categories: self-inductance type and mutual inductance type.
Inductive displacement sensors are electromechanical conversion devices that are widely used in modern industrial production science and technology, especially in automatic control systems, machining and measurement industries.
