current in seven control lines. The primaries of the "A" 

 transformers in all of the packages are connected in series; 

 similarly the "B" transformers; etc. Thus, the control 

 circuits have the same "fail-safe" feature as the power circuit. 



Calibration of the temperature and pressure sensors is 

 accomplished by remotely switching the frequency control of 

 the telemetering oscillator to one or more sets of calibrated 

 resistors. Switching is accomplished by sending a control 



signal which excites the primary windings of the calibration 

 circuit transformers of all packages. The output from the 

 secondary is rectified and caused to operate a relay which 

 effects the necessary switching from sensor to calibration 

 resistors. In order to avoid the unnecessary power drain 

 incurred by operating relays in all packages, the calibration 

 signal is applied to a 2-input "and" gate along with the output 

 of the 7-input control "and" gate so that only the relay in 

 the package being interrogated is operated. Inclusion of 

 one calibration circuit allows the control of the oscillator 

 frequency to be switched from sensor to one set of calibration 

 resistors. Addition of a second calibration circuit would 

 add two more calibration points, should this be desirable. 

 It is probable that one circuit will suffice since the real 

 purpose of the "calibration" is to apply a check on the 

 proper operation of the telemetering system. 



91 



