TRANSDUCERS 



may either remain fixed with the coil assembly or may be incorporated in the 

 moving armature. 



Many configurations are possible: two common ones are shown in 

 Figure 33.12. The compliance of the transducer is dictated entirely by the 



Tension 

 wire ^^ 



Soft iron 

 armature 



Spring 



S 



N 



Coil 



-Tension 

 , wire 



Moving 

 'magnet 



Magnet 



(a) 



-Soft iron 

 pole pieces 



Jlontrol 

 spring 





//////// 



(b) 



Figure 33.12 Two moving-iron transducers shown diagrammatically 



1 



Driving, 

 rod 



Flexible 

 diaphragm 



Magnet 



Soft iron 

 pole pieces 



Coil wound on 

 light former, with 

 '' flexible lead-out 

 wires 



Figure 33.13 Section of moving-coil transducer 



spring on which the armature is mounted, and it may be chosen to suit the 

 application. It is not possible to give any figures for output voltage, as it 

 depends upon the number of turns on the coil, the strength of the magnet and 

 on the geometry of the armature and coil assembly. 



The relationship between the output voltage and input velocity with a 

 moving-iron transducer is inherently non-linear. Although the non-linear 

 effects can be minimized by operating the transducer over only a small range 

 of displacement, moving-iron transducers are best regarded as only suitable 

 for qualitative work. 



Moving-coil transducers — If a coil is moved through a uniform stationary 



484 



