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BELL SYSTEM TECHNICAL JOURNAL 



its spacing contact. The small delay required in the operation of 

 relay 2 with respect to relay 1 is obtained by connection of condenser 

 C2 around the windings of relay 2. 



SIGNAL 



VOLTAGE OF 

 CONDENSER C. 



REFC.E 



Fig. 23 — Variation of charge on measuring condenser in 

 telegraph service-monitoring set. 



If at the time of the momentary comparison between the condenser 

 and reference voltages these two voltages are equal, no current will 

 flow in the peak distortion indicator. This condition can be obtained 

 for marks of unit duration (for instance the duration of a selecting 

 pulse of the teletypewriter code) by suitably adjusting the reference 

 voltage REFC. E. For marks of longer duration however the con- 

 denser voltage will exceed the reference voltage but, by properly 

 poling the rectifier in series with the peak-distortion indicator, current 

 is effectively prevented from flowing at the time of the momentary 

 comparison. With this poling of the rectifier the current flowing due 

 to the marks being shorter than unit duration will affect the peak- 

 distortion indicator and if suitably adjusted will cause a gas-filled 

 tube to operate and thereby give an indication of distortion. 



It will be apparent that the measurements of spaces may be accom- 

 plished by providing for that purpose another circuit of the same type 

 as that of Fig. 22. For the measurement of both marks and spaces 

 four relays are required, but only one peak-distortion indicator is 

 necessary. 



Associated with the measuring circuit is a counting circuit which 

 counts the number of excessive distortions experienced in a given 

 time. This circuit is indicated schematically by Fig. 24. In this 

 circuit the charge of the condenser C is mixed with that of a larger 

 condenser C2 at each operation of the gas-filled tube of the distortion 

 measuring circuit. Thus the charge on the larger condenser becomes 

 an indication of the number of excessive distortions. By arranging a 

 timer to discharge this condenser through an indicating circuit suitably 



