MEASUREMENT OF TELEGRAPH TRANSMISSION 



177 



designed an alarm may be obtained whenever the number of exces- 

 sive distortions exceeds any predetermined number up to about 7 

 within a given time. For this purpose another gas-filled tube is 



/T~g\i GAS TUBE 

 ' ^ ^ PLATE 



FIG. 22 



Fig. 24 — Counting and alarm circuit of telegraph service-monitoring set. 



employed having a potentiometer associated with it for the purpose of 

 adjusting the grid-biasing potential so that the tube will fire only for 

 voltages exceeding definite amounts corresponding to definite numbers 

 of excessive distortions. It is apparent that this type of counting 

 circuit could be replaced by a counting-relay circuit or by a selector- 

 switch circuit such as is used in automatic telephony. 



A front view of the monitoring set, arranged for mounting on a 

 relay rack in a central office, is shown by Fig. 25. 



In the present arrangement these sets have jacks at a number of 

 places along the telegraph board in the central office, for the purpose 

 of permitting attendants to use the set conveniently. Alarm lamps 

 and signals are provided at the board to attract the attention of the 

 attendant. As the use of these sets is developed, it may be found 

 desirable to employ them in conjunction with a patrol arrangement by 

 means of which a given set may be connected in turn to each of a 

 number of circuits for a short interval. An arrangerrient of this sort 

 was described by W. Schallerer.^ 



Other Developments 



Other types of measuring apparatus have been used experimentally 

 in the Bell System and have been found of value in laboratory work 



