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BELL SYSTEM TECHNICAL JOURNAL 



detector thereby initiating the operation of relay Z. At the same time, 

 another set of contacts of relay W close the charging circuit of con- 

 denser Ci thereby permitting the charging of this condenser through 

 the high resistance Ri. These conditions remain unchanged until the 

 armature of relay Z has reached its tn contact and caused the operation 



B,:i: 



, T I 



[Oscilll"* 

 i-atorj — 



r 1 \.^<u— 



' Detector I L^SS^ ! 



1 r- 



L 



Fig. 2 



of relay X. The latter relay first opens the charging circuit of con- 

 denser Ci and then causes the operation of relay Y. The operation of 

 relay F discharges the two condensers Ci and C2 through the differential 

 meter circuit composed of the meter M and the two equal resistances 

 i?5 and i?6- Additional resistances R^ and Ri are connected into the 

 discharge circuit to limit the discharge current and prevent sparking 

 at the relay contacts. 



If the meter shows no deflection at the instant of discharge, it 

 indicates that the two charges are equal and that the operating time of 

 relay Z is as indicated by the value of resistance Ri. If the meter 

 shows a deflection, the key K should be opened and closed repeatedly 

 and the resistance Ri adjusted until the meter shows no deflection. 



In order to prevent a quick double deflection of the meter when a 

 balance has been reached, it is necessary that the time constant of the 

 two branches of the discharge circuit be approximately alike. For this 

 reason, the ratio Ri + Rs to R3 + R^ of the discharge circuit resistances 

 should be approximately the same as the ratio Ci to C2 of the condenser 

 capacities. 



The releasing time of relay Z; that is, the time required for the 

 armature to leave its w contact after the oscillator is removed from the 

 detector, may be measured by making a few simple changes in the 



