Inductive sensors find wide application in mechanical engineering, food, textile and other industries. They are most effectively used as limit switches in the automatic lines and machines, as inductive sensors work only on metal and not sensitive to other materials.

Inductive sensor - this is primarily contactless switch, which contains no moving parts and is virtually impossible to influence the environment. The main purpose - contactless position control objects, made of conductive materials or magnetopowder.

From sensors, based on other principles, but created for the same purpose, inductive sensors have a number of significant differences and advantages, featuring high durability, due to the absence of collisions and technical impacts, sensitivity only to metal and the ability of various embodiments. Such sensors do not respond to fluid, lubrication, the touch of the hand, that is very convenient and practical in the production process.

Inductive sensors are simpler and cost less, than capacitive and ultrasonic. The design of the sensor provides protection against short circuit and the possibility of functioning in a temperature range from -25 to + 70 ° C.

Other advantages of such sensors include: the simplicity and durability of construction, the absence of sliding contacts; the ability to connect to sources of industrial frequency; a relatively large output power (to tens of Watts); significant sensitivity.

 Advantages

- No mechanical wear, no failure, stand’s associated with the contacts

- There is no contact bounce false positives

- High switching frequency up to 3000 Hz

- Resistant to mechanical stress

Disadvantages - relatively low sensitivity, the dependence of inductive reactance on frequency of the supply voltage, a significant inverse impact on sensor measured value (due to the attraction of the armature to the core).

Contact sensors - this is the simplest type resistor sensors, which convert the displacement of the primary element in a stepwise change in resistance of the electric circuit. With the help of contact sensors measure and control efforts, moving, temperature, dimensions’objects, control their shape and t. d. Contact sensors include travel and limit switches, contact thermometers, the so-called electrode sensors, used primarily for measurement of maximum levels of conductive liquids.

Contact sensors can operate in constant, and alternating current. Depending on the limits of the measurement probes can be single limit. The latter is used to measure values, what changed within considerable limits, the resistor R, included in the electrical circuit, consistently shorted.

The lack of contact sensors - the difficulty of implementation of continuous control and the limited life of the contact system. But thanks to the extreme simplicity of these sensors they are widely used in automation systems.

Capacitive sensors - the principle of operation is based on the dependence of the electrical capacitance of the capacitor with the dimensions, the mutual arrangement of plates and dielectric constant of the medium between them.

Capacitive sensors, as well as inductive, eat alternating voltage (usually high frequency - to tens of megahertz ). The measuring circuits are usually used for bridge scheme and the scheme using resonant circuits. In the latter case, as a rule, use the dependence of the oscillation frequency of the oscillator from the capacitance of the resonant circuit, that is, the sensor has a frequency output.

The advantages of capacitive sensors - easy, high sensitivity and low inertia. Disadvantages - the influence of external electric fields, the relative complexity of measuring devices.

Capacitive sensors used to measure angular displacements, very small linear displacements, vibration, speed and t. D., as well as for playback of the given functions ( harmonic, sawtooth, rectangular and t. p.).

Potentiometric the sensor is a variable resistor, to which the supply voltage is interrupted, its input value is the linear or angular displacement tacos’negative contact, and output value - voltage, remove from that contact, that changes its size when you change its position.

Potentiometric sensors are used to convert linear or angular displacement into an electrical signal, and for playback the simplest functional dependence in automatic devices and automatic continuous type.

The advantages of potentiometric sensors:

1.             simple design;

2.             small dimensions and weight;

3.             a high degree of linearity of the static characteristics;

4.             stability characteristics;

5.             ability to work on AC and DC.

The disadvantages of potentiometric sensors:

1.             the presence of sliding contact , which can cause cracks due to oxidation of the contact paths , chafing of turns or bending the slider;

2.             error in operation due to the load;

3.             a relatively small conversion factor;

4.             high sensitivity;

5.             the presence of noise;

6.             the tendency electroiron under the action of pulsed discharges.

Thermocouple are the high temperature contact temperature sensors. The principle of operation of thermocouple is based on thermoelectric effect, open German physicist Thomas Sam in 1821 g. If you’to unite two dissimilar conductor and maintain the place’Union at different temperatures, between the ends of electromotive force will arise (the thermo-EMF ). Such’of unity are called thermocouples. The emerging value of the thermopower depends on the material of conductors and the temperature difference between the junctions. In a small temperature range voltage is proportional to the temperature difference.

The main advantage of thermocouples is the large temperature measurement range from -200 ° C to 2500 ° C, as well as the simplicity and strength of the structure , and low price. The main disadvantages of thermocouples - the accuracy of the measurement from 1 ° C, the need for temperature compensation of cold junction (in modern devices introduced an automatic correction to the measured EMF), nonlinear dependence of output voltage of a thermocouple from temperature.

Digital semiconductor temperature sensors recently actively promoted by the agricultural market. Sensitive elements for them to produce world leaders in the field of microelectronics. The sensing element is an integrated circuit, that contains the sensing element and the transducer into a digital signal.

The main advantages of these sensors: convenient connection diagram (does not require laying individual cable lines directly to the sensor, the sensors are connected to one line), digital signal, avoiding the use of different converters for the construction of the measuring circuit, and low price. The disadvantages of these sensors are an extremely weak immunity (sensors can seriously lie, if there is a power line or electric motors work) and low accuracy (only 0,5 ° C). Limited operating range of these sensors - to 125 ° C - does not allow to apply them in various heat transfer systems, where the temperature can reach 130-150 ° C.