Manual

Issue 2, January 2020 Model 47A User Guide
Page 24 Studio Technologies, Inc.
Model 47A’s 2-wire connectors will result
in a continuous cycle of 4-seconds on
(three seconds for start up and one sec-
ond for detection) and 6-seconds off.
Auto Null
Each of the Model 47A’s 2-channel inter-
faces has circuitry to automatically null the
two 2-wire-to-4-wire interfaces. Normally
this process is performed at the time of ini-
tial Model 47A configuration but there’s no
reason why auto nulling can’t be initiated
anytime one desires. The only time that
auto null must be performed is if condi-
tions have changed vis-à-vis the intercom
user devices and wiring connected to a
Model 47A 2-wire PL interface connector.
Even a slight change to an intercom cir-
cuit, such as adding or removing a section
of cable, is sufficient to require that the
auto null process be performed.
Two buttons, one associated with each
interface, are provided to activate the
auto null process. Refer to Figure 11 for a
detailed view. To initiate auto null simply
requires tapping (pressing and releasing)
a button. The process begins by nulling
channel 1 of an interface and, when com-
pleted, moves on to channel 2. Two LEDs
provide a visual indication of the auto
null process, flashing when the auto null
process for its respective channel is active.
An actual auto null sequence starts by
muting the 4-wire input and output signal
paths associated with the specific channel
to be nulled. Then a short period of 24 kHz
signal is sent out the 2-wire PL intercom
interface channel. This will turn off micro-
phones on those connected user devices
that are compatible with the RTS TW-Series
“mic kill” protocol. The actual auto nulling
process will next be performed. A series of
tones will be sent out the 2-wire interface.
Other Model 47A circuitry, under software
control, will rapidly perform adjustments to
achieve the best null possible. After the ad-
justments are made the results are stored
in non-volatile memory. Once the process
has completed the 4-wire input and output
paths are again activated.
Advanced configuration DIP switch 2, locat-
ed on the back panel, allows an indepen-
dent auto null button mode to be selected.
If DIP switch 2 is in its on (up) position,
the front-panel pushbuttons will function
in quite a different manner. In the indepen-
dent mode, a single tap to a button will
cause channel 1 to auto null. Two taps will
cause channel 2 to auto null. By observing
the operation of the two auto null status
LEDs it will become readily apparent which
of the button modes has been selected.
If possible, prior to performing an auto null
it’s polite to warn all personnel who are
actively using the connected intercom de-
vices. The tones sent to the 2-wire intercom
circuit during the nulling process are not
excessively loud or obnoxious, but most
users might want to remove their headsets
during the process. In addition to warning
users, it might be a good time to ask them
to mute any active microphones. While
Figure 11. Detail of front panel showing auto
null section