Instructions for testing telegraph lines and the technical arrangements of offices (1878)
Schwendler, Louis, 1838-1882 · London : Trèubner · leaf 151
should be able to call the sending station at anymoment during the transmission of a message. 136 OFFICE TESTING. XIII. Discharging Key.—The principle of sucli anarrangement will be clear from Fig. 5, which representsthe diagram of a discharging hey. 1, 2, and 3 are adjustable electrical contacts.… … When the key is sending, then contact 2 is open andcontacts 1 and 3 are closed. Hence, between the send-ing and the receiving position of the key, there will be aposition in which contacts 2 and 3 are closed and con-tact 1 is open. Thus, if contacts 2 and 3 are made tolast simultaneously for a…
Telegraph · Telegraph lines
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