Sensors and transducers

1) Typology of sensors:

to)       position sensors

b)       speed sensors

c)       acceleration sensors

 

2) Typology of position sensors:

to)       Potenziometri

b)       Transformers Differentiate them Linear

c)       Sincro & Resolver

d)       codified Masks

 

3) Typology of speed sensors:

a) tachimetrica Dynamo

b)    Masks increases them

 

4) Typology of acceleration sensors:

to)       piezoresistivi Accelerometers (extensometer)

b)       Accelerometers to feedback

 

5) Potenziometro:

It is constituted from an insulating support on which a having resistore is found a resistance to unit of length, can is sagomato in rectilinear shape or to circle arc, on the resistance slides a connected mobile cursore to the position that is wanted to be measured, varying the varied position the resistance, while with potenziometri the circulars the variations can be measured angle irons. If the resistance is constituted from a wire, it can be wrapped on the insulating support and that determines a discontinuity when the cursore passes from a coil successive therefore to the resolution is equal to the inverse one of the coil number, while the resistivo element is infinite in the case is constituted from a metallic film.

Two outlines to partitore are used:

to)       to an end of the resistance there is the positive clip and to the other end there is the mass, the cursore is towards the cargo

b)       the resistance comes fed from a duale generator and the mass connected to its point is had centers them.

The potenziometro precise one is a transducer much but it is strongly subject to vibrations and corrosion and its characteristic is to delineate single in cargo absence.

 

6) Transformer differentiates to delineate them :

It is used for the measure of linear translations, it is constituted from connected a secondary support of not ferromagnetic material on which an alternated fed primary winding is had in and two identical ones in opposition of phase. To the inside there is a mobile ferromagnetic nucleus, if it is arranged symmetricalally regarding the 2 windings, marks them total is null, otherwise a various reluctance is had and therefore in escape one sinusoide is had whose amplitude is function of the movement l, moreover from a phase measure is also possible to estimate the back of the movement.

The sensibility of the instrument increases is to growing of the frequency (…must but to hold account that to growing of w increases the stiffness of the head physician and therefore diminishes the current circolante) that to growing of the tension (…must in this case to hold account that beyond a sure tension the nucleus is saturated and problems of Joule effect are had also).

In kind inferior frequency and tensions to 50V between 50Hz are used and 10Khz.

 

7) Synchro:

It is a sensor of position used for the measure of angles, in particular the angle is that one of which the rotor fed is moved in alternated regarding the reference position. On the stator there are of the windings trifase on which induce the tensions to empty , .

sending such tensions to an electronic discriminatore it is succeeded to determine the angle q. Tensions from 12V are used to 115V to frequencies between 50Hz and 400Hz obtaining sensibility of 100mV/°.

 

8) Resolver :

It is a sensor of position used for the measure of angles, in particular the angle is that one of which the rotor fed is moved in alternated regarding the reference position. On the stator such tensions to an electronic discriminatore are 2 windings disposed to 90° between they on which to empty can be measured the tensions , sending are succeeded to determine the angle q. Tensions from 12V are used to 115V to frequencies between 50Hz and 400Hz obtaining sensibility of 100mV/°.

 

9) codified Mask :

A lot used is a transducer laddove is demanded one measure of linear or angular movement directly in digital shape them. With reference to the case of movements angle irons, the mask comes mail on the organ in spin, it is constituted from a disc subdivided in fields and circular crowns, on every element of characterized area therefore is present a binary information 0-1 that that form the present number on a data settoree that consetuamente is the binary transcription of the natural numbers, which can ulteriorly then be codified in BCD. Binary information 0-1 can correspond to one more or less conductive, more or less opaque zone. Problems are had because in passing from one it codifies to the successive one is in railroad that in BCD varies more than a bit and this can give place to errors in order to obviate to which is rerun to the Gray code.

 

10) Extensometer to resistance :

Draft of a transducer action to be moderate a deformation, ve of is two typology :

to)       extensometer to resistance

A placed resistivo support is had on the material of which it interests to measure the lengthening, has from which ottiene of the rest it is had that the variation of the S section of the thread is tied to the variation of volume from the relation of Poisson and also that the resistività variation r is tied to the variation of volume from the , after all is obtained therefore where K is the calibration factor.

For having measurable variations of resistance threads of infinitesimal section would be necessary, in order to obviate to that a structure to ghirigoro in which the features curves they come realizes to you with wide section and therefore null resistance is come true. Particular cure goes held in the incollaggio and the dependency from the temperature.

b)       piezoelectric extensometer

It uses of semiconductors for which is much fort variation of resistività consequent to variation of volume (…phenomenon called piezoelectricity), relation reaches similar to that one that it is had for the extensometers to resistance, with the difference that for the piezoelectric extensometers K much more is elevated and therefore they are more sensitive, introduce but the defect of one greater dependency from the temperature.

 

11) tachimetrica Dynamo :

A stator constituted from a permanent magnet is had that therefore produces a constant flow, the rotor is constituted from N coils and finishes on a collector broken from which a tension can be captured proporziona them to the spin speed, to it but a legacy to the coil number is added ripple.

 

12) Masks increase them :

Draft of a sensor of speed with escape in digital shape them, is come true with a mask that comes mail on the spin organ, such mask is subdivided in transparent or alternatively opaque fields. In the case the optical reader uses itself, for a mask of 15cm can itself be had until to 2¹⁵ steps for turn. In order to distinguish the spin back two taccheggiature sfasate between they and two optical readers are used.

It can be used simply also for the measure of movements counting the n° of the steps.

 

13) piezoresistivo Accelerometer :

The mass subject to the acceleration is connected through an extensometer to a fixed point, when the mass moves the extensometer is become deformed and therefore through a measure of resistance with a bridge of Weathstone the acceleration can be calculated impressa.