The nonferrous-metal type incorporates an oscillation circuit in which energy loss caused by the induction current flowing in the target affects the change of the oscillation frequency. When a nonferrous-metal target such as aluminum or copper approaches the sensor, the oscillation frequency increases. On the other hand, when a ferrous-metal target such as iron approaches the sensor, the oscillation frequency decreases.
When the oscillation frequency becomes higher than the reference frequency, the sensor outputs a detection signal. Magnetic objects and non-magnetic objects Remember that magnetic objects are easily attracted by a magnet, whereas non-magnetic objects are not.
Variable inductance and variable reluctance sensors typically produce an electrical signal proportional to the displacement of a conductive or magnetically permeable object normally a steel rod relative to a coil. As with the proximity sensor, the impedance of a coil varies in proportion to the displacement of the target relative to a coil energised with an alternating current. Such devices are commonly used to measure the displacement of pistons in cylinders — for example in pneumatic or hydraulic systems.
The piston can be arranged to pass over the outer diameter of the coil. Synchros measure the inductive coupling between coils as they move relative to each other. They are usually rotary and require electrical connections to both moving and stationary parts typically referred to as the rotor and stator.
They can offer extremely high accuracy and are used in industrial metrology, radar antennae and telescopes. Synchros are notoriously expensive and are increasingly rare nowadays, having mostly been replaced by brushless resolvers. These are another form of inductive detector but electrical connections are only made to windings on the stator.
LVDTs, RVDTs and resolvers measure the change in inductive coupling between coils, usually referred to as primary and secondary windings.
The primary winding couples energy into the secondary windings but the ratio of energy coupled into each of the secondary windings varies in proportion to the relative displacement of a magnetically permeable target. 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. For example, an inductive sensor can also monitor liquid levels with the help of metal floaters. This versatility makes it a valuable tool in all industrial areas as well as in a multitude of machines.
How does an inductive sensor work? What is the difference between flush and non-flush sensors? What is the difference between nominal switch distance Sn and real switch distance Sr? Working with inductive sensors: the advantages and disadvantages at a glance. Buying an inductive sensor. It registers a contact to an inserted object without touching it. The sensor has an active surface — an oscillator — on its front. This emits an electromagnetic field in a semicircle. A metal object being inserted in the field will weaken this field.
This allows the sensor to detect how far away the object is — and act accordingly. Depending on the model, the measuring distance ranges from 0.
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