Inductive sensor

Elements of a simple inductive sensor.
1. Field sensor
2. Oscillator
3. Demodulator
4. Flip-flop
5. Output

An inductive proximity sensor is a type of non-contact electronic proximity sensor that is used to detect the position of metal objects. The sensing range of an inductive switch is dependent on the type of metal being detected. Ferrous metals, such as iron and steel, allow for a longer sensing range, while nonferrous metals, such as aluminum and copper, can reduce the sensing range by up to 60 percent.[1] Since the output of an inductive sensor has two possible states, an inductive sensor is sometimes referred to as an inductive proximity switch.[1][2]

The sensor consists of an induction loop. Electric current generates a magnetic field, which collapses generating a current that falls toward zero from its initial trans when the input electricity ceases. The inductance of the loop changes according to the material inside it and since metals are much more effective inductors than other materials the presence of metal increases the current flowing through the loop. This change can be detected by sensing circuitry, which can signal to some other device whenever metal is detected.

Common applications of inductive sensors include metal detectors, traffic lights, car washes, and a host of automated industrial processes. Because the sensor does not require physical contact it is particularly useful for applications where access presents challenges or where dirt is prevalent.

Whereas an inductive proximity sensor measures the absence or presence of a target, an inductive position sensor measures the position of a target along a measurement path. The path may be rotary, linear, curvi-linear or, even, two dimensional. Inductive position sensors work using the same basic physics as an electrical transformer. Such sensors include synchros, resolvers, rotary and linearly variable differential transformers (RVDTs & LVDTs) and inductive encoders (or incoders).[3]

Traditional inductive position sensors typically comprise a metal rod or rotor that moves relative to a set of wire wound coils which are energised with an AC signal. As the rod or rotor moves either the inductance of the wire wound coils varies or the electromagnetic coupling between the coils varies. Traditional inductive sensors have a good reputation for reliability and robustness but are bulky, heavy and expensive.

Inductive encoders (or incoders) are a more recent technique. They use the same physical principles as inductive proximity and position sensors but use printed laminates rather than wire wound coils.[3] Printing rather than winding is a more precise and less expensive production technique -enabling such sensors to be more accurate, more reliable, less costly and more compact than traditional inductive devices.

Inductive encoders are frequently used for safety critical applications in the aerospace, defence, medical and petrochemical sectors.

See also

References

  1. 1 2 Frank Lamb (2013). Industrial Automation: Hands-On. McGraw-Hill Education. pp. 74–75. ISBN 9780071816458.
  2. ↑ "Inductive sensors". September 1, 2001. Retrieved December 29, 2015.
  3. 1 2 "How Inductive Sensors Work". www.zettlex.com. Retrieved 25 September 2016.


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