Sec. 1-2] 



MECHANICAL INPUT TRANSDUCERS 



87 



rise to a d-c potential difference. The transfer characteristic, i.e., the 

 output voltage 7? versus the displacement x, is shown in Fig. ( 1 -2) 686. 

 The potential difference can reach values of more than 100 volts. The 

 sensitivity of the arrangement, AE /Ax, can reach values up to 

 several volts per micron of displacement. The phenomenon can be 

 observed from very low excitation frequencies (60 cps) up to the 

 microwave region. For technical reasons, operation between 0. 1 and 

 1 Mc is recommended. Accurate frequency stability is not required 

 for the operation of the transducer. The lifetime of the tube can be 



(a) 



(b) 



*t-Eo 



Fig. (1-2)68. Ionization transducer: 

 («) basic circuit; (b) transfer charac- 

 teristic [figures (1-2)68 and (1-2)6!) 

 from K. S. Lion, Rev. Sci. Instr., 27, 

 222 (1956); by permission]. 



{a) 



\b) 



Fig. (1-2)6!). Ionization transducer 

 system for large movements: (a) 

 schematic diagram; (b) transfer 

 characteristic. 



considerably increased by arranging the plates P x and P 2 in such a 

 way that the glow discharge is largely confined to that part of the 

 tube opposite the electrodes. This is the cross-hatched part of the 

 tube in Fig. (1-2) 68a. The glow surrounding the electrodes A and B 

 is then reduced, and cathode sputtering is eliminated. 



The arrangement of Fig. (1-2)68 is useful for the conversion of 

 displacements up to about 1 mm. Figure (1-2)69 shows a transducer 

 system for large movements up to several inches. The tube T is 

 filled with gas under reduced pressure. One side of a high-frequency 

 source S is connected through capacitors C x and C 2 to the internal 



