REI^IVS IN THE PELL SYSTEM 41 



If satisfactory tfli-^jr.ipli si-rvico is to l)i' riTuliTiil, partifularK- on 

 long circuits iiivol\iiig a numl)cr of relayinjj points, it is essential 

 that the telegraph relays employetl have such operating character- 

 istics that they intr(xliice as little ilistortion to the signals as possible. 

 It has been founil that the polarized type of relay fulfills this con- 

 dition to a greater extent than the neutral type of relay which is 

 used in local circuits and in some telegraph circuits where extreme 

 accuracy is not required. The polar relay permits arrangements of 

 circuits which minimize the effect of poor wave shape and line leak- 

 age. It also is more easily adapted to variations in current strength 

 and may be adjustetl to give more accurate repetition of the signals 

 under all conditions. 



A number of important developments in telegraph relays lia\e 

 leil up to the relay shown in Fig. 29. This relay gives reliable opera- 

 tion with 4-ampere turns in the winding and by careful adjustment 

 may be made to operate on a small fraction of that. 



Fig. 29 — Photograph of telegraph type relay 



While the telegraph relay may be called upon to operate on very 

 small energ\% its contact must be capable of handling much larger 

 quantities. Due to the speed of operation desired and to the de- 

 pendence on accurate transmittal of each impulse the contacts must 

 operate without chatter or vibration. Great care has been taken in 

 the design of the relays and the circuits to protect the contacts and 



