Sec. 1-6] 



MECHAXICAL IXPUT TRANSDUCERS 



123 



output impedance, which increases the influence of external disturb- 

 ances. The requirements for accessory equipment can be con- 

 siderable. A commercial inductive flow meter is shown in Fig. (1-6)4. 



1-63. Thermal Flow-velocity Transducer 



The method devised for the study of blood flow velocity in animal 

 experiments ("Thermo-Stromuhr") by Rein 1 is analogous to that 



Fig. (1-6)4. Exploded view of an electromagnetic-induction transducer for flow- 

 velocity measurement in liquids (courtesy of The Foxboro Company, Foxboro, Mass.). 



described earlier (1911) by C. C. Thomas for the measurement of 

 flow velocity in gases (1 66). 



The instrument is illustrated schematically in Fig. (1-6)5. The 

 blood flowing in a vessel A is heated in an rf electric field between the 



1 H. Rein, Z. Biol., 87, 394 (1928). 



