Polarity Inversion On Exchange - Canon FACSIMILE BASIC 2000 Service Manual

6. POLARITY INVERSION ON
EXCHANGE
The Fig. A-16 shows the standard operation of an exchange in order to
explain polarity inversion. This example is for an exchange operating in
Japan. The polarity on the calling side is reversed simultaneously with the
called party becoming offhook. The original polarity is restored simulta-
neously with the end of the telephone conversation and the called party
becoming onhook.
On some facsimiles, the characteristics of the telephone line are used when
to perform auto-dialing.
Polarity is not reversed on some exchanges overseas and some private
branch exchanges.
Telephone State Operation of Exchange
1
Monitors states of
Both
terminals.
onhook
(normal state)
2 Calling party Exchange is started up.
offhook Dial tone is sent to calling
(loop closed) party.
3
Transmission of
Operation of exchange
dialing signal
Selects the called party.
4 Calling called
Selects the called party,
party in progress
inverts the polarity and
sends the calling
identification.
Sends the ringing back tone
to the calling party.
Restores original polarity
5
Called party
after response from called
offhook
party.
(loop closed)
Deactivates the calling
identification.
Inverts the polarity on the
6
Voice transmission
calling party and
deactivates the ringing
back tone.
7 End of call Restores all lines to their
Both onhook
original states.
Fig. A-16 Example of Standard Operation of Exchange in Japan
Telephone Line State
Calling party Called Party
Exchange
– 48V – 48V
+ Earth + Earth
Long high-
pitched sound
– 48V – 48V
+ Earth + Earth
Dial tone
Dialing signal
– 48V – 48V
+ Earth + Earth
Ringing back
tone
– 48V + Earth
+ Earth
– 48V
Ringing back tone Calling identification
+ Earth
– 48V
+ Earth
– 48V
– 48V – 48V
+ Earth + Earth
1
2
3
4
5
6
A
çi
A–21