of injection. The choice of hot or cold is made by the main 

 tank temperature controller (fig. 6) which consists of a 

 quartz thermometer* coupled to a digital comparator. ** 

 The signal from the quartz-crystal sensor located in the 

 calibration tank (fig. 4b) is compared with a temperature 

 set-point dialed on the comparator by the operator. 

 Depending on the direction of temperature offset, the 

 comparator (fig. 6) switches the hot and cold solenoid 

 calves on or off through relays designed to handle the 

 necessary current. The quartz-thermometer digital- 

 comparator combination operates as a coupled system. 

 Later, a digital-to-analogue converter and a Varian strip- 

 chart recorder (figs. 6, below, and 8, page 17) were added 

 to the control system to give a continuous and permanent 

 record of tank temperature throughout any operation. Some 

 advantages of the new system are: direct digital readout of 

 tank temperature in degrees centigrade (one-second sampling 

 rate with resolution to 0. 001°C); increased temperature range 

 to include the 85 °C required for reversing thermometer 



VARIAN STRIP 

 CHART RECORDER 



DIGITAL-TO-ANALOG 

 CONVERTER 



QUARTZ THERMOMETER" 

 DIGITAL READOUT 



ir->=*p--w- 



TEMPERATURE 

 CONTROLLER UNIT 

 (COMPARATOR) 



NULL DETECTOR 

 MUELLER BRIDGE 



Figure 6. Temperature controller with Mueller bridge and null defector. 



*DYMEC Quartz Thermometer Model 2801 A. 

 **DYMEC Digital Comparator Model 2539 A. 



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