Manual

Model 47A User Guide Issue 2, January 2020
Studio Technologies, Inc. Page 19
Auto Null Button
One pushbutton switch is associated with
each of the Model 47A’s two interface
circuits. An advanced configuration pa-
rameter allows selection of the button’s
operation. The choices are dual auto null
and independent auto null. When dual
auto null is selected a single tap of one of
the two front-panel pushbutton switches
initiates a routine that begins with chan-
nel 1’s auto null sequence taking place
followed immediately by channel 2’s auto
null sequence being performed. Note that
the configuration selected for auto null
button operation will also apply to the
remote auto null inputs.
Independent auto null allows the auto null
function to be initiated for each channel as
desired. A single tap will start the auto null
routine for channel 1. Two taps will start
the routine for channel 2.
Referring to Figure 8, when DIP switch 2 is
in its off (down) position dual auto null is
selected. This is provided specifically for
cases where the Model 47A’s 2-wire party-
line interfaces will be used with 2-channel
intercom user devices. As an example: the
RTS TW-Series provides two independent
audio channels, as well as power, over a
single 3-conductor cable. In a case such
as this it’s useful for both of the hybrid
circuits associated with an interface to be
auto nulled at approximately the same
time. Dual auto null allows a single tap of
the button to initiate nulling of both hybrid
circuits.
When DIP switch 2 is in its on (up) position
independent auto null is selected. This
would be appropriate for applications in
which the two audio paths associated with
each interface are used with independent
party-line intercom circuits. This situation
might arise when two Clear-Com single-
channel intercom circuits are connected to
one of the Model 47A’s 2-channel interfac-
es. The hybrid circuit associated with each
channel can be auto nulled as desired.
Another example would be in an RTS
TW-Series application that uses source
assignment panels. These SAP panels
would be used to route multiple intercom
channels to various sets of user devices
as desired. In this case, the two channels
associated with each Model 47A interface
will often end up not routed to the same
user device; independent auto nulling is
certainly desired.
Pin 3 Power Disable
The Model 47A was designed to provide
independent DC power sources and im-
pedance terminations on pin 2 and pin 3
of both party-line interfaces. These re-
sources are appropriate where the Model
47A is installed in conjunction with a
source assignment (SAP) panel or cus-
tomer pin assignment method. In this way,
no matter how pins 2 and 3 are ultimately
assigned to dual-channel user beltpacks,
such as RTS BP-325, power will always be
supplied to operate the beltpacks. There
are some special situations where pin 3
of the Model 47A’s two interfaces may
require impedance termination but not a
Figure 8. DIP Switch 2—Auto Null Button