MAGNETIC DRUM TRANSLATOR FOR TOLL SWITCHING OFFICES 737 



tive voltage excursion at point b, during a pulse, so that it never goes 

 below +105 volts. This establishes the uniform pulse amplitude among 

 Ithe forty match channels which is necessary for proper functioning of 

 the unit. 



To detect and recognize the voltage conditions at the five junction 

 points, two varistor gates and a differential amplifier are employed. One 

 gate, comprising six varistors including vr6 and VRii, will transmit the 

 type of mismatch signal which is more positive than +115 volts. This 

 signal is dc-coupled to the left-hand grid of the differential amplifier as 

 illustrated in Fig. 12. The type of mismatch signal which is less positive 

 than +115 volts is blocked by this gate but is transmitted through the 

 other gate to the right-hand grid. The threshold for this discriminating 

 action is established by application of a fixed nominal potential of +115 

 volts to varistors VRii and vri2. 



At match, the output of each of the two gates presents a potential of 

 + 115 volts to the differential amplifier. The differential amplifier is bi- 

 ased (by inequality of r7 and rs) so that for this condition the right- 

 hand triode is conducting, and the output potential is lower than the 

 plate supply voltage. Positive-going mismatch signals on the left-hand 

 [grid, or negative-going signals on the right-hand grid are then equally 

 jeffective in cutting oft' the right-hand triode, causing the output voltage 

 to rise to plate supply potential signifying a mismatch. 



The outputs from the differential amplifiers of the eight match units 

 are combined with the a sync pulses in a system of and gates, as illus- 

 trated in Fig. 4. A match-pulse output from this system thus signifies 

 that conditions for match have been uniquely determined for 40 pairs 

 [of items. Thus the match unit, in total, is capable of distinguishing be- 

 jtween all binary combinations of 40 bits or approximately 10'^ items al- 

 I though when a self-checking code is employed, as in the translator appli- 

 cation, many of these combinations are inadmissible. 



(2) The A Gate-Opening Pulse 



Occurrence of the match-pulse, as just described, indicates that the 

 40 items constituting one-half the contents of one of the a slots match 

 the incoming input code; it is then desired to spill out from the other 

 half of this same a slot the information which is also appearing at ampli- 

 Ifier outputs at that instant. This is done by means of gates opened by 

 the action of a gate-opening pulse, triggered by the match pulse. 



The a gate-opening pulse is only a few microseconds in duration and 



normally is produced only once per revolution of the drum; a quiescent 



[blocking-oscillator was chosen as the type of circuit best suited for this 



[purpose. Whenever the code-check relays are operated in an authentic 



