Canon fax basic 2000 서비스 매뉴얼
BASIC OF TELEPHONE
1–8
2.4
Hook Button
When a hook button is closed by picking up a handset, direct current flows
to the telephone circuits.
Fig. 1-9 Hook Button
The purpose of this is twofold (i) so that direct current is made to flow to
the transmitter to provide current for sending voice when the handset is
picked up, and (ii) so that the exchange detects this direct current to recog-
nize that the handset has been picked up.
Fig. 1-10 DC Loop
Picking up a handset is called “making a DC loop”. A DC loop lets the
exchange know that:
(1) The calling party (the party making the call) is ready to call someone.
(2) The called party answered. (The party receiving the call)
(3) The handset is on-hook.
Hook button
Hook button
T: Transmitter
R: Receiver
HS: Hook switch
R
T
HS
Exchange
Telephone
Direct
current
detector
current
detector
Detects direct
current.
current.
Closed when a handset is
picked up. (Off-hook state)
picked up. (Off-hook state)
Direct current (DC) loop