STATIC MECHANOELECTRICAL TRANSDUCERS 



The photoelectric transducer, illustrated diagrammatically in Figure 33.21, 

 has become particularly convenient since the introduction of the extremely 

 small phototransistor (Chapter 28). Small transducers of good sensitivity, 



75k 



573A 



Output Set 1 100 k 



zero 



300 V 



Figure 33.20 Circuit for RCA 5734 transducer 



Converging lens 

 with square mask 



Bulb 



Phototransistor 



Moving vane 

 Figure 33.21 Photoelectric transducer 



Mask and vane 

 with identical grids 



Bulb 



Phototransistor 



Figure 33.22 Photoelectric transducer for very small displacements 



which need no contact with the preparation, can now be constructed. The 

 upper frequency limit of such a transducer is set by : (a) the cut-off of the 

 photocell — 3 kc/s for a phototransistor ; (b) the resonant frequency of the 

 vane, which by careful design can be made as high as several kc/s. 



The sensitivity of a photoelectric transducer using a plain aperture (as 

 illustrated) may be about 50 V/cm. This can be increased many-fold by 

 using a double grid to reduce the apparent aperture ; this is shown in Figure 

 33.22. 



491 



