Self-inductance of the coil changes as you approach it magnetically permeable body, so the movement of the body relative to the coil can be detected by a sensitive coil self-induction transmitters that use this principle yavlyayutsya.obychno proximity (Fig. 1a). In addition, there are associated inductive displacement transducers (Fig. 1b), in which the coil core is mechanically connected to the body, the movement of which is measured. Proximity transducers described type are used as a base for the construction of inductive proximity sensors and inductive switches approximation.
Figure 1. Inductive displacement transducer: a - non-contact, b - associated
Magnetic displacement transducers.
Converters of this type are based on the principle of change of the magnetic resistance between two or more magnetic coils excited by an alternating current, depending on the movement of the body. The latter fact is the output voltage of the converter. Transformative element is performed so that it can be used in different types of devices, in which the conversion of the measured physical quantity in the movement. This defines the measured value.
• Electromagnetic sensors have the following advantages:
the simplicity and cheapness of construction, mechanical strength, high reliability due to the possibility of removal of the output signal without sliding contacts, power supply from industrial network frequency of 50 Hz, the possibility of obtaining a sufficiently high output power, possibility to work in the range of small (fractions of mm) and large (meters) displacement.
The disadvantages of electromagnetic sensors should include the effect on the output signal of an external electromagnetic field and the frequency of the supply voltage, as well as the ability to work only on alternating current (the direct current power supply is only possible for induction sensors.
The change of inductance and vzaimoinduktivnosti can occur under the influence of mechanical stresses in the core of the electromagnetic sensor. Such stresses lead to a change in the magnetic permeability of the ferromagnetic material of the core. Electromagnetic sensors, based on a physical phenomenon called the magneto-elastic sensors.
Electromagnetic sensors (inductive, transformer, inductive, magnetoelastic) is widespread in automation systems.