DRY CELLS 



SUPPLYING 



BRIDGE POTENTIALS 



TWO BANKS 

 OF EIGHT BRIDGE 

 ASSEMBLIES EACH 



Figure A4. Bridge assembly for sixteen-channel temperature measuring unit. 



the sixteen channels ordinarily requires about a half a minute, but the time de- 

 pends on the differences in temperature of the points being measured. It is con- 

 ceivable that, if each alternate point of temperature were at opposite ends of the 

 range thus forcing the recorder bead to travel the full scale for each printing, 

 the time for a full cycle would be 72 seconds. This, however, would be an ex- 

 treme case. 



The unbalance in the bridges is caused by changing resistance in K4 brought 

 about by the changing temperature of the thermistor beads which are part of that 

 arm. Thus, potential can be translated into temperature, by means of previous 

 calibration of the recorder against known temperatures. 



The difference of potential between the bridge arms and the potentiometer is 

 amplified by a Brown amplifier, so that it can drive a servomechanism. The servo 

 moves the sliding contact in the potentiometer circuit until the applied potential 

 from the thermistor bridge and the reference potential are equal. The reference 

 potential is supplied by a dry cell whose voltage is standardized automatically 



32 



