Sec. 1-2] 



MECHANICAL IX PUT T RAXS I)PC EPS 



73 



an output signal. No data on the performance of this transducer are 

 reported. 



b. Position Convectron. A sealed glass bulb with two arms (Fig. 

 (1-2)57, is filled with an inert gas such as argon and contains a nickel 

 wire running centrally through each arm. The wire is electrically 

 heated to a temperature of about 400°C; cooling occurs primarily by 

 convection. The convection current, and thus the temperature and 

 the resistance of the nickel wire, depend upon the angular position of 



Base 



<VT5w^ -o- -Tinnpo 



Fig. (1-2)56. Thermal displace- 

 ment transducer {after G. A. 

 Shakespear, British Pat. 219,- 

 452). 



Fig. (1-2)57. Thermal displacement 

 transducer for rotary movement, con- 

 vection type. 



the arm with respect to the direction of gravitation (arrow); the 

 resistance of the wire will increase in one arm and decrease in the 

 other if the transducer is rotated from the zero position. The trans- 

 ducer is usually connected into a resistance bridge. 



The displacement signal can be as high as 50 m V/deg in the vicinity 

 of the zero position. The sensitivity varies with the applied voltage 

 and reaches a maximum at about 10 volts. Operation at direct 

 current is recommended for the measurement of very small angles. 



The transducer can be used for an angular movement of 360°; it 

 permits the detection of angular displacements as small as 1 angular 

 second with proper stabilization of the supply voltage and of the 

 ambient temperature. 



The output impedance of the convectron transducer varies be- 

 tween 50 and 200 ohms, depending upon the applied voltage; its 

 time constant is about 0.1 sec. The noise level is 1 to 5 mV at a-c 

 operation and considerably less at d-c operation. Random air cur- 

 rents striking the tube and ambient-temperature variation are likely 

 to cause errors. The power requirements are less than 1 watt. 



The main advantages of the position convectron transducer are 



