Studio Technologies 47A - Manual (Page 23)

Model 47A User Guide Issue 1, September 2014
Studio Technologies, Inc. Page 23
software responds to this condition by
turning off the power source on that spe-
cific pin and flashing its associated LED as
a warning. After a 6-second “cool-down”
interval the output returns to the same
condition as upon initial power-up: power
is again applied to the pin, the pin status
LED will light, and monitoring won’t begin
for another three seconds. A full short-cir-
cuit condition applied to the Model 47A’s
2-wire connectors will result in a continu-
ous cycle of 4-seconds on (three seconds
for start up and one second 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 circuit,
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 10 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 independent
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.
Figure 10. Detail of front panel showing auto
null section