TRANSDUCERS 



TRANSDUCERS FOR CONTINUOUS ROTATION 



All the devices described in this section lie within the field of servomechanism 

 engineering. Since this field is a particularly wide and diflicult one, a brief 

 description will be given of only those devices which might have some 

 application in biological research. Thus for a.c. servomotors and generators, 

 rotating amplifiers and special-purpose servo techniques, the reader should 

 consult the extensive literature now available on servomechanisms'^'^'^. 

 Before discussing rotating devices under the headings of m-e and e-m 

 transducers, systems which might formally be called mechano-electro- 

 mechanical will be described under their more usual name of 'synchronous 

 links'. 



Synchronous links 



It is frequently necessary to transmit shaft rotations over paths so long 

 or tortuous that flexible shafts or belts are impracticable. For these purposes 

 pairs of electrically interconnected devices known as synchronous links 

 are available. These may be used in very low-power applications, such as 

 for driving indicating pointers, or where considerable power is transmitted ; 

 the underlying principles are similar. 



D.c. synchronous links — The Desynn is illustrated in Figure 33.29. The 



Transmitter Receiver 



Figure 33.29 The Desynn 



variation of current in the three windings of the receiver due to the rotation 

 of the transmitter shaft causes the receiver shaft to turn synchronously. 

 Desynns are useful only as low-power links, and are commonly used for 

 indicating the position of a shaft remotely. 



The M-motor {Figure 33.30) uses a similar receiver configuration, but 

 moves discontinuously in 12 steps per revolution. Quite high power may 

 be transmitted by devices of this type. Torques of 150 g-cm and speeds up 

 to 200 rev/min can be achieved with an M-motor of 2 in. diameter and 

 2 in. long. When step-wise motion is of no consequence, as for instance 

 when a considerable step-down gear ratio is used, the M-motor provides 

 a most convenient source of remotely controlled power. 



A.c. synchronous links — The principle of the majority of a.c. synchronous 

 links is illustrated in Figure 33.31. The currents induced in the stator 

 windings of the transmitter give a magnetic field configuration in the 

 receiver which pulls the two shafts into synchronism. 



When used as a low-power link for indication only, a simple and light 



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