RECORDER 



Fig. 5. System block diagram. 



E.T.O. SIGNAL 



Fig. 6. 



Linearizing and range changing 

 block diagram. 



recorder such that a 10 C change in sea surface 

 temperature produces a full span deflection of 

 the recorder. 



As indicated in Fig. 5> the temperature con- 

 troller precisely maintains the reference cavity 

 at 50°C ±0.02°C. The cavity temperature is 

 sensed by a thermistor bead embedded in the 

 cavity and used as one arm of a Wheatstone 

 bridge. The error signal from the bridge con- 

 trols a thyratron which proportions the current 

 through the heating element of the cavity. A 

 second thermistor bead, located within the cavity, 

 is used to monitor the cavity temperature. 

 Changes in resistance of this bead are monitored 

 by the reference bridge circuit. The bridge 

 output is displayed on the reference temperature 



meter which is calibrated to read cavity tempera- 

 ture directly in degrees Centigrade. 



Thermistor operation requires a DC bias which 

 is developed by the electronic bias supply. It 

 originates in a 5 Kcps transistorized oscillator. 

 The output voltage is stepped up and then recti- 

 fied to produce an output of ^300 volts. The 

 DC output voltage is additionally filtered and 

 highly stabilized using RC networks and zener 

 diodes. 



The DC power required for operating the vari- 

 ous circuits is obtained from a transistorized 

 regulated power supply operating from the 

 117 volt 60 cps line. The supply also provides 

 a highly regulated output at 26.5 volts. 



In an effort to produce a precision instrument 

 of high reliability, considerable attention has 

 been given to design fundamentals. These include 

 temperature stabilization of the detector, the 

 cavity and optical elements, compensation of the 

 preamplifier and detector at 20 cps to provide 

 a nearly perfect flat response to eliminate the 

 effects of chopper speed variation and reduction 

 of the dynamic range over which circuits are 

 required to operate to insure a high degree of 

 linearity. In addition, extreme care has been 

 taken in the choice of circuits, selection of 

 components and method of fabrication to achieve 

 a highly stable electronic system, e.g., large 

 amounts of feedback are used in the preamplifier; 

 silicon transistors are employed to avoid 



65 



