TRANSDUCERS 



The tuning inductor of the oscillator in Figure 33.35 has an open magnetic 

 circuit, and is varied by the movement of a mumetal armature. The output 

 of the oscillator is converted into square waves by the limiting valve, and 



•+150V 



47k A7k Output 



0005 



'/26J6 EF91 V26AL5 V26AL5 



Figure 33.35 Circuit for variable inductance transducer 



these square waves feed a 'pulse counter discriminator'^^ which gives a d.c. 

 output voltage proportional to the frequency of the oscillations. Once 

 again the frequency of oscillation must be high compared with the signal 

 frequency. 



Press to 

 balance 



-oTIo » O+60 V 



120 > 



R.RC. 



.—-j^^nrm^-^Output 



1-5$ 9X ?X 



^u-uui f ' • — ^ . I 



From 

 transducer 



-60V 



12AT7 



Tuned to 

 same frequency 



Transducer 



Figure 33.36 Circuit for use with capacitance transducer 



502 



