Sec. 1-2] 



ME( 11. 1 SIl 'A L IXI'I T TRANSDUCERS 



85 



be very good. The fact that the output appears in the form of a 

 variable frequency signal can be advantageous in digital systems. 



For literature references, see O. Schaefer, Z. Ver. deut. Ing., 63, 1008 (1919); 

 R. S. Jerret, J. Sci. Tnstr., 22, 29 (1945). 



h. Electronic Displacement Transducers. The plate current in a 

 space-charge-limited vacuum tube isafunctionof theelectrodegeom- 

 etry. In a diode with a plane parallel anode and cathode of an area 

 a spaced by a distance d, the electron current is 



/ =2.34 x 10- 6 X %,E l 



d z 



E is the applied plate voltage. The plate current can be changed by 

 variation of the separation d. 



A diode transducer based upon this principle is described by Day 1 

 and is shown schematically in Fig. (1-2)66. It consists of an evacu- 

 ated tube, closed at one end with a flexible membrane; the cathode 



Fig. (1-2)66. Moving- 

 anode displacement 

 transducer used for 

 the measurement of 

 pressure, schematic 

 diagram. 



Fio. (1-2)67. 

 Moving - anode 

 t r ansducer , 

 schematic dia- 

 gram (mec/;«no- 

 electronic trans- 

 ducer tube, RCA 

 type 5734). 



assembly C is held in a fixed position, while two anodes A x and A 2 are 

 held by a stem supported in the center of the membrane. A variation 

 of the diaphragm position increases the distance from the cathode to 

 one anode and decreases that to the other anode. The system is used 

 in a bridge arrangement; the transfer characteristic (voltage in the 



1 G. Day, J. Sci. Instr., 26, 372 (1949). 



