STATIC MECHANOELECTRICAL TRANSDUCERS 



The inductance of the transducer will not in general vary linearly with the 

 displacement of its armature. In addition, the circuits with which such 

 transducers are used do not necessarily give an output which is a linear 



Coil 



Armature of 

 stalloy or 

 mumetal \ 



1 



Tension 

 wire ~ 



Moving 

 core of 

 magnetic 

 material 



mm 



stalloy 

 diaphragm 



Coil 



Laminated 

 core 



Ferrite 

 pot core 



(a) (b) (c) 



Figure 33.16 Some variable inductance transducers shown diagrammatically 



function of the inductance. It is possible to correct these non-linearities 

 with specially shaped armatures, but it is more usual to restrict the range of 

 operation to a small fraction of the possible armature travel; over such a 

 range the output of the circuit is virtually linear with displacement. 



A particularly convenient form of variable inductance transducer is the 

 'differential transformer', some examples of which are shown in Figure 33.17. 



3 equally 



spaced 



coils 



Pivoted 

 armature 



Output 



Core of 



magnetic _ 

 material Energizing 

 voltage 



Flexible 



magnetic 



armature 



Output 



(a) 



Energizing 

 voltage 



(b) 



Energizing 

 voltage 



Laminated 

 core 



(C) 



Figure 33. 1 7 Differential transformers 



The symmetrical construction gives improved linearity and an output which 

 falls to zero at the central position of the armature. However, if operation 

 on either side of this position is required, special circuits are necessary 

 (see page 501). 



Variable capacitance transducers 



If one plate of a capacitor is moved relative to the other, the capacitance 

 between them will vary. Figure 33.18 shows a number of transducers based 

 on this principle. 



489 



